2005 JGR-Space Physics Papers making use of ACE Data
in their Investigations. No ACE team members on author list.
(78 Papers)
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Variations
of polar cap index in response to solar wind changes and magnetospheric substorms
Huang C.-S.
(2005), Variations of polar cap index in response to solar wind changes and
magnetospheric substorms,
J. Geophys. Res., 110, A01203, doi:10.1029/2004JA010616.
2005-01-08
Abstract: The polar cap (PC) index is used to measure the
geomagnetic activity over the polar caps. Changes in the solar wind are
able to cause disturbances in the magnetospheric-ionospheric
currents, which in turn cause variations in the PC index. In order to
understand how different processes in the solar wind and magnetosphere
influence the PC index, it is necessary to separate the effects of solar
wind pressure impulses, interplanetary magnetic field (IMF) reorientations,
and magnetospheric substorms.
We study the variations of the PC index under different solar wind
conditions and during substorms and present case
analyses and statistical results. The main conclusions are as follows. A
solar wind pressure impulse alone, without IMF southward turning or substorm, is to cause a negative spike of ∼1 in the PC index within a time interval of 2–6 min and a
subsequent increase to a positive value of ∼1 within 30 min. The
PC index enhances significantly after the IMF turns southward, and the
increase of the PC index is 3–5 in most cases and can be as large as 8–9.
When a solar wind pressure impulse occurs with a simultaneous southward
turning of the IMF, the large increase of the PC index is mainly a response
to the southward IMF but not to the solar wind pressure impulse.
Magnetospheric substorms have significant effects
on the PC index. The response of the PC index to substorms
is an increase of 2–4 in most cases and can reach 6 or larger. The effects
of IMF southward turnings and substorms on the PC
index are much stronger than that of solar wind pressure impulses. On
average, the increases of the PC index caused by solar wind pressure
impulses, substorm onsets, and IMF southward
turnings are 0.8, 3.2, and 3.6, respectively.
Copyright
2005 by the American Geophysical Union.
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Necessary
conditions for geosynchronous magnetopause crossings
Suvorova A., A. Dmitriev, J.-K. Chao, M. Thomsen, Y.-H. Yang (2005), Necessary
conditions for geosynchronous magnetopause crossings, J. Geophys. Res., 110, A01206, doi:10.1029/2003JA010079.
2005-01-14
Abstract: The International Solar Terrestrial Physics database of
the magnetic measurements on GOES and plasma measurements on Los Alamos
National Laboratory (LANL) geosynchronous satellites is used for selection
of 169 case events containing 638 geosynchronous magnetopause crossings (GMCs) in 1995 to 2001. The GMCs
and magnetosheath intervals associated with them
are identified using advanced methods that take into account (1) strong
deviation of the magnetic field measured by GOES from the magnetospheric field, (2) high correlation between the
GOES magnetic field and interplanetary magnetic field (IMF), and (3)
substantial increase of the midenergy ion and
electron fluxes measured by LANL. Accurate determination of the upstream
solar wind conditions for the GMCs is performed
using correlation of geomagnetic activity (Dst
(SYM-H) index) with the upstream solar wind pressure. The location of the GMCs and associated upstream solar wind conditions are
ordered in an aberrated GSM coordinate system (aGSM) with X-axis directed along the solar wind flow.
In the selected data set of GMCs the solar wind
total pressure Psw varies up to 100 nPa and the southward IMF Bz
reaches 60 nT. We study the conditions necessary
for geosynchronous magnetopause crossings using scatterplots
of the GMCs in the coordinate space of Psw versus Bz. In such a
representation the upstream solar wind conditions show a sharp envelope
boundary beyond which no GMCs are observed. The
boundary has two straight horizontal branches where Bz
does not influence the magnetopause location. The first branch is located
in the range of Psw = 21 nPa
for large positive Bz and is associated with a
regime of pressure balance. The second branch asymptotically approaches the
range of Psw = 4.8 nPa
under strong negative Bz, and it is associated with a regime in which the Bz influence saturates. The intermediate region of the
boundary ranges from moderate negative to moderate positive IMF Bz and can be well approximated by a hyperbolic tangent
function. We interpret the envelope boundary as a range of necessary
upstream solar wind conditions required for the magnetopause to reach
geosynchronous orbit at its closest approach to the Earth (its “perigee”
location).
Copyright
2005 by the American Geophysical Union.
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Formation
and motion of a transpolar arc in response to dayside and nightside reconnection
Milan S. E., B.
Hubert, A. Grocott (2005), Formation and motion
of a transpolar arc in response to dayside and nightside
reconnection, J. Geophys. Res., 110, A01212, doi:10.1029/2004JA010835.
2005-01-19
Abstract: We trace the formation and subsequent motion of a
transpolar arc in response to dayside and nightside
reconnection. Both high- and low-latitude dayside reconnection are
observed, as well as periods of substorm and nonsubstorm nightside
reconnection, during the 7-hour interval of interest on 19 January 2002. We
speculate that the arc is formed by a burst of nonsubstorm
nightside reconnection and that its subsequent
motion is controlled predominantly by the rate of dayside high-latitude
reconnection, siphoning open flux from the dusk sector polar cap to the
dawn sector. The observations allow us to quantify the rates of
reconnection: on the nightside, 35 and 100 kV
during nonsubstorm- and substorm-related
bursts, respectively; on the dayside, 30 and 100 kV for high- and
low-latitude reconnection. The latter values give effective merging line
lengths of 1 and 5.5 R E for northward and southward interplanetary
magnetic field, respectively. We suggest that transpolar arc motion will be
controlled not only by the B y component of the IMF but also by the
relative magnitude of the B z component, when ∣ B y ∣ >
B z motion will be dawnward for B y < 0 nT and duskward for B y >
0 nT; however, when B z > ∣ B y
∣, we expect that the arc will move toward the noon-midnight
meridian of the polar cap.
Copyright
2005 by the American Geophysical Union.
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Characteristic
magnetic field and speed properties of interplanetary coronal mass
ejections and their sheath regions
Owens M. J., P.
J. Cargill, C. Pagel, G. L. Siscoe,
N. U. Crooker (2005), Characteristic magnetic field and speed properties of
interplanetary coronal mass ejections and their sheath regions, J. Geophys. Res., 110, A01105, doi:10.1029/2004JA010814.
2005-01-20
Abstract: Prediction of the solar wind conditions in near-Earth
space, arising from both quasi-steady and transient structures, is
essential for space weather forecasting. To achieve forecast lead times of
a day or more, such predictions must be made on the basis of remote solar
observations. A number of empirical prediction schemes have been proposed
to forecast the transit time and speed of coronal mass ejections (CMEs) at 1 AU. However, the current lack of magnetic
field measurements in the corona severely limits our ability to forecast
the 1 AU magnetic field strengths resulting from interplanetary CMEs (ICMEs). In this study
we investigate the relation between the characteristic magnetic field
strengths and speeds of both magnetic cloud and noncloud
ICMEs at 1 AU. Correlation between field and
speed is found to be significant only in the sheath region ahead of
magnetic clouds, not within the clouds themselves. The lack of such a
relation in the sheaths ahead of noncloud ICMEs is consistent with such ICMEs
being skimming encounters of magnetic clouds, though other explanations are
also put forward. Linear fits to the radial speed profiles of ejecta reveal that faster-traveling ICMEs
are also expanding more at 1 AU. We combine these empirical relations to
form a prediction scheme for the magnetic field strength in the sheaths
ahead of magnetic clouds and also suggest a method for predicting the
radial speed profile through an ICME on the basis of upstream measurements.
Copyright
2005 by the American Geophysical Union.
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Interplanetary
consequences caused by the extremely intense solar activity during
October–November 2003
Tokumaru M., M. Kojima, K. Fujiki, M.
Yamashita, D. Baba (2005), Interplanetary consequences caused by the
extremely intense solar activity during October–November 2003, J. Geophys. Res., 110, A01109, doi:10.1029/2004JA010656.
2005-01-28
Abstract: We report interplanetary scintillation (IPS) measurements
made by the 327 MHz four-station system of the Solar-Terrestrial
Environment Laboratory of Nagoya University, during 21 October to 8
November 2003. In this period, solar activity increased greatly owing to
the appearance of huge eruptive sunspots on the solar disk. Interplanetary
(IP) disturbance events traveling from the Sun beyond the Earth's orbit
have been detected clearly from our IPS observations in association with
most of the major eruptive events that occurred on the Sun during that
period. A possible link between solar/IPS events and near-Earth (IP shock)
events in that same period was investigated in this study. As a result, an
IP counterpart was identified by our IPS observations for all of the shock
events which occurred during the period, and the link to solar events was
established unambiguously for the majority of shock events on the basis of
the identification of their IP counterparts. Among the IP disturbance
events, the most prominent one occurred between 28 and 29 October 2003, and
it is considered as an IP counterpart to the 28 October X17 flare event.
Our IPS data revealed a complex feature of this IP disturbance and
demonstrated that the global distribution of the solar wind density
turbulence settled into a rather quiescent condition after the X17 event
except between 2 and 4 November 2003, despite the occurrence of marked
solar activities. This is in clear contrast to the fact that enhancements
of the turbulence level had taken place frequently before the event. The
lack of marked g-value enhancements for those events is considered partly
due to the intrinsic effect related to a change in the global distribution
of the solar wind turbulence and partly due to artificial effects inherent
in our IPS observations. The radial expansion of the IP disturbance was tracked
successfully by consecutive IPS observations during the period between 2
and 4 November in association with the 2 November X8.3 flare event. The
movement of this IP disturbance inferred from IPS data was found to be
generally consistent with the average transit speed of the IP shock
associated with the X8.3 event, although some deceleration of the IP
disturbance may have taken place.
Copyright
2005 by the American Geophysical Union.
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Low-energy
neutral atom signatures of magnetopause motion in response to southward B z
Collier M. R.,
T. E. Moore, M.-C. Fok,
B. Pilkerton, S. Boardsen, H. Khan (2005), Low-energy
neutral atom signatures of magnetopause motion in response to southward B
z, J. Geophys. Res., 110, A02102, doi:10.1029/2004JA010626.
2005-02-03
Abstract: We report an event observed by the Low-Energy Neutral Atom
(LENA) imager on 18 April 2001, in which enhanced neutral atom emission was
observed coming from the direction of the Sun and from the general
direction of the subsolar magnetopause. The
enhanced neutral atom emission is shown to be primarily a result of
increased solar wind charge exchange with the Earth's hydrogen exosphere,
that is, enhanced neutral solar wind formation, occurring in conjunction
with a southward turning of the interplanetary magnetic field (IMF) which
moves the magnetopause closer to the Earth. It is shown that the neutral
atom flux under compressed magnetopause conditions is extremely sensitive
to changes in the IMF north-south component.
Copyright 2005
by the American Geophysical Union.
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Origins
and variation of terrestrial energetic neutral atoms outflow
Wilson G. R.,
T. E. Moore (2005), Origins and variation of terrestrial energetic neutral
atoms outflow, J. Geophys. Res., 110, A02207, doi:10.1029/2003JA010356.
2005-02-11
Abstract: Analysis of ENA data from the LENA instrument on the IMAGE
spacecraft shows that the terrestrial atmosphere is a copious emitter of
energetic neutral atoms (<300 eV) under all
conditions. When activity is low, the observed emissions are concentrated
close to the Earth and are presumed to be the high-energy tail of the warm
oxygen geocorona, with energies <2 eV. When activity increases, the relative abundance of
the higher-energy neutrals increases, and the
emissions can be seen farther from the Earth. Because of the close
correlation between the postperigee ENA flux
(fluxes seen 1–2 hours after spacecraft perigee) and Ap
and the fact that the postperigee fluxes are seen
when no magnetic storm is in progress we conclude that many of the emitted
ENA come from the auroral zone and are produced
by energized ionospheric ions rather than by
precipitating energetic ions. In more spectacular events, such as the
Bastille Day storm event (14–16 July 2000), oxygen neutral emissions
produced by precipitation of keV ring current
oxygen ions can also make an important contribution to the total neutral
emission. We conclude that diurnal variation in ENA emissions is a winter
hemisphere feature that is absent in the summer hemisphere. As activity
increases, the altitude range of the auroral oval
ENA emission region increases.
Copyright
2005 by the American Geophysical Union.
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High-altitude
cusp flow dependence on IMF orientation: A 3-year Cluster statistical study
Lavraud B., A. Fedorov, E. Budnik, M. F. Thomsen, A. Grigoriev,
P. J. Cargill, M. W. Dunlop, H. Rème, I. Dandouras, A. Balogh (2005),
High-altitude cusp flow dependence on IMF orientation: A 3-year Cluster
statistical study, J. Geophys. Res., 110, A02209,
doi:10.1029/2004JA010804.
2005-02-15
Abstract: We report on the statistical properties of the plasma
flows measured by the Cluster spacecraft in the high-altitude cusp region
of the Northern Hemisphere as a function of the interplanetary magnetic
field (IMF) orientation, with selected clock angle intervals. The technique
uses a magnetic field model, taking into account the actual solar wind
conditions and level of geomagnetic activity, in order to model the
magnetopause and cusp displacements as a function of these conditions. The
distributions of the magnetic field vector show a clear consistency with
the IMF clock angle intervals chosen and demonstrate that the technique
used here fixes the positions of the cusp boundaries adequately. The antisunward convection observed in the exterior cusp
suggests that this region is statistically quite convective under southward
IMF, while for northward IMF the region appears more stagnant. The presence
of large parallel (downward) flows at the equatorward
edge of the cusp shows that plasma penetration occurs preferentially at the
dayside low-latitude magnetopause for southward IMF conditions; in
contrast, under northward IMF the results are suggestive of plasma
penetration from the poleward edge of the cusp,
combined with a substantial sunward convection, but no flows are observed
at all at the dayside boundary with the plasma sheet. The comparison of the
measured flow speed with the Alfvén speed
suggests that the magnetosheath adjacent to the
external boundary is more sub-Alfvénic, even for
high magnetic latitudes, under northward IMF than under southward IMF. This
result is consistent with the preference for the plasma depletion layer to
develop under such conditions. The transverse plasma convection in the
exterior cusp appears to be controlled by the IMF B Y component as well;
for dawnward (duskward)
IMF orientations the convection is preferentially directed toward dusk
(dawn). These results are interpreted as strong arguments in favor of the
cusp being structured, at large scales, by the occurrence of magnetic
reconnection at the high-latitude magnetopause for northward IMF and at the
low-latitude magnetopause for southward IMF.
Copyright
2005 by the American Geophysical Union.
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Solar
wind spatial scales in and comparisons of hourly Wind and ACE plasma and
magnetic field data
King J. H., N.
E. Papitashvili (2005), Solar wind spatial scales
in and comparisons of hourly Wind and ACE plasma and magnetic field data,
J. Geophys. Res., 110, A02104, doi:10.1029/2004JA010649.
2005-02-16
Abstract: Hourly averaged interplanetary magnetic field (IMF) and
plasma data from the Advanced Composition Explorer (ACE) and Wind
spacecraft, generated from 1 to 4 min resolution data time-shifted to Earth
have been analyzed for systematic and random differences. ACE moments-based
proton densities are larger than Wind/Solar Wind Experiment (SWE)
fits-based densities by up to 18%,
depending on solar wind speed. ACE temperatures are less than Wind/SWE
temperatures by up to ∼25%. ACE densities and temperatures were normalized to
equivalent Wind values in National Space Science Data Center's creation of
the OMNI 2 data set that contains 1963–2004 solar wind field and plasma
data and other data. For times of ACE-Wind transverse separations <60 R
E, random differences between Wind values and normalized ACE values are ∼0.2 nT for ∣ B ∣, ∼0.45 nT for IMF Cartesian components, ∼5 km/s for flow speed, and ∼15 and ∼30% for proton densities and temperatures. These
differences grow as a function of transverse separation more rapidly for
IMF parameters than for plasma parameters. Autocorrelation analyses show
that spatial scales become progressively shorter for the parameter
sequence: flow speed, IMF magnitude, plasma density and temperature, IMF X
and Y components, and IMF Z component. IMF variations have shorter scales
at solar quiet times than at solar active times, while plasma variations
show no equivalent solar cycle dependence.
Copyright
2005 by the American Geophysical Union.
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Dynamic
Harris current sheet thickness from Cluster current density and plasma
measurements
Thompson S. M.,
M. G. Kivelson, K. K. Khurana,
R. L. McPherron, J. M. Weygand, A. Balogh, H. Réme, L. M. Kistler (2005), Dynamic Harris current sheet thickness
from Cluster current density and plasma measurements, J. Geophys. Res., 110, A02212, doi:10.1029/2004JA010714.
2005-02-19
Abstract: We use the first accurate measurements of current
densities in the plasma sheet to calculate the half-thickness and position
of the current sheet as a function of time. Our technique assumes a Harris
current sheet model, which is parameterized by lobe magnetic field B 0,
current sheet half-thickness h, and current sheet position z 0. Cluster
measurements of magnetic field, current density, and plasma pressure are
used to infer the three parameters as a function of time. We find that most
long timescale (6–12 hours) current sheet crossings observed by Cluster
cannot be described by a static Harris current sheet with a single set of
parameters B 0, h, and z 0. Noting the presence of high-frequency
fluctuations that appear to be superimposed on lower frequency variations,
we average over running 6-min intervals and use the smoothed data to infer
the parameters h (t) and z 0 (t), constrained by the pressure balance lobe
magnetic field B 0 (t). Whereas this approach has been used in previous
studies, the spatial gradients now provided by the Cluster magnetometers
were unavailable or not well constrained in earlier studies. We place the
calculated half-thicknesses in a magnetospheric
context by examining the change in thickness with substorm
phase for three case study events and 21 events in a superposed epoch
analysis. We find that the inferred half-thickness in many cases reflects
the nominal changes experienced by the plasma sheet during substorms (i.e., thinning during growth phase,
thickening following substorm onset). We conclude
with an analysis of the relative contribution of ∂ B Z /∂ X to
the cross-tail current density during substorms.
We find that ∂ B Z /∂ X can contribute a significant portion of
the cross-tail current around substorm
onset.
Copyright
2005 by the American Geophysical Union.
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How
good is the relationship of solar and interplanetary plasma parameters with
geomagnetic storms?
Kane R. P.
(2005), How good is the relationship of solar and interplanetary plasma
parameters with geomagnetic storms?, J. Geophys. Res., 110, A02213, doi:10.1029/2004JA010799.
2005-02-25
Abstract: Since the work of Snyder et al. (1963), who showed a
possible link between interplanetary solar wind speed V and geomagnetic
index Kp, such a relationship has been examined
by many workers and found to be rather loose. In the present communication
this relationship is rechecked for all data during 1973–2003. It was noted
that moderate or strong geomagnetic storms occurred only when solar wind
speed V was above ∼350 km/s. However,
above this limit, the plots of Dst versus V
showed a large scatter, and any value of V could be associated with any
value of Dst in a wide range of a factor of ∼2, or any Dst value could be
associated with any value of V in a wide range of a factor of ∼2, indicating a poor relationship between V and Dst. The scatter could be partly because not V but VB s
(product of V and the southward component B s of interplanetary field B) is
the appropriate variable relevant for Dst
changes. This was checked. In the plot of Dst
versus VB s it was noticed that the scatter was smaller and correlation
better than that in the plot of Dst versus V.
Since the relationship between V and Dst is poor,
an estimate of V with some antecedence, as is done in a present-day
prediction scheme ((Gonzalez et al., 2004) V estimated from the lateral
extension speed of side halo coronal mass ejections (CMEs)
and assuming V 2 proportional to Dst magnitudes)
is not likely to give reliable estimates of Dst
magnitudes. However, estimate of V could certainly be useful to estimate
the time when the storm would hit the Earth but remembering that
15% of the halo CMEs may miss the
Earth.
Copyright
2005 by the American Geophysical Union.
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Coupled
response of the inner magnetosphere and ionosphere on 17 April 2002
Goldstein J.,
J. L. Burch, B. R. Sandel, S. B. Mende, P. C:son Brandt, M. R.
Hairston (2005), Coupled response of the inner magnetosphere and ionosphere
on 17 April 2002, J. Geophys. Res., 110, A03205,
doi:10.1029/2004JA010712.
2005-03-04
Abstract: We present an observational study of the global dynamics
of the plasmasphere, aurora, ring current, and subauroral
ionosphere on 17 April 2002 during a substorm.
Global observations by the Imager for Magnetopause-to-Aurora Global
Exploration (IMAGE) and in situ observations by DMSP F13 provide a
comprehensive view of the coupled response of the inner magnetosphere and
ionosphere. At 1900 UT a substorm onset initiated
a sunward convective impulse, which caused a ring current injection. The
motion of this impulse past the plasmasphere
caused ripples to propagate along the plasmapause,
eastward and westward from premidnight magnetic
local time (MLT). The motion of the ripples agrees exceptionally well with
the motion of the aurora and the ring current, implying strong coupling.
The westward moving ripple (on the duskside)
participated in a two-phase plasmapause
undulation effect. In the first phase (1915 UT to 1936 UT), a mild 0.4–0.5
R E bulge formed near 2000 MLT, probably caused by an E-field induced by
local reduction of the magnetic field by the ring current pressure
increase. In the second phase (1936 UT to 2037 UT) this mild bulge was
removed by a subauroral polarization stream
(SAPS) westward flow that stripped away the outer 1 R E of the duskside plasmasphere. The
SAPS effect was observed in the ionosphere by DMSP between about 1930 UT
and 2000 UT and is evident in vector E-fields inferred from plasmapause motion. All the observations of this event
suggest strong coupling among the plasma populations of the
magnetosphere-ionosphere system. This event represents the first
identification of the directly observed global plasmaspheric
effects of a substorm-driven impulse, the SAPS
flow channel, and the ring-current magnetic field reduction.
Copyright
2005 by the American Geophysical Union.
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Some
characteristics of intense geomagnetic storms and their energy budget
Vichare G., S. Alex, G. S. Lakhina
(2005), Some characteristics of intense geomagnetic storms and their energy
budget, J. Geophys. Res., 110, A03204, doi:10.1029/2004JA010418.
2005-03-04
Abstract: The present study analyses nine intense geomagnetic storms
(∣ Dst ∣ > 175 nT) with the aid of ACE satellite measurements and ground
magnetic field values at Alibag Magnetic
Observatory. The study confirms the crucial role of southward IMF in
triggering the storm main phase as well as controlling the magnitude of the
storm. The main phase interval shows clear dependence on the duration of
southward IMF. An attempt is made to identify the multipeak
signature in the ring current energy injection rate during main phase of
the storm. In order to quantify the energy budget of magnetic storms, the
present paper computes the solar wind energies, magnetospheric
coupling energies, auroral and Joule heating
energies, and the ring current energies for each storm under examination.
Computation of the solar wind- magnetosphere coupling function considers
the variation of the size of the magnetosphere by using the measured solar
wind ram pressure. During the main phase of the storm, the solar wind
kinetic energy ranges from 9
Copyright
2005 by the American Geophysical Union.
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Solar
zenith angle and merging electric field control of field-aligned currents:
A statistical study of the Southern Hemisphere
Wang H., H. Lühr, S. Y. Ma (2005), Solar zenith angle and merging
electric field control of field-aligned currents: A statistical study of
the Southern Hemisphere, J. Geophys. Res., 110,
A03306, doi:10.1029/2004JA010530.
2005-03-22
Abstract: High-resolution and precise vector magnetic field
measurements of the CHAMP satellite are used to investigate the
field-aligned currents (FACs) in the southern
polar ionosphere. The period considered comprises 2 years, providing a
double coverage of the seasons and about a six-fold coverage of all local
times. From more than 11,000 polar passes the average spatial pattern of FACs in the polar ionosphere is derived. The response
of features like intensity and positions of large-scale field-aligned
currents to normal (when merging electric field is less than 2 mV/m) and
disturbed (when merging electric field is greater than 2 mV/m) conditions
in the Southern Hemisphere are investigated. The influence
of the solar illumination-induced conductivity on the morphology features
of field-aligned currents during normal conditions are also studied.
It follows from this analysis that the intensity of field-aligned currents
changes with the merging electric field at all MLT sectors but with the
solar radiation-induced conductivity only at the dayside. Furthermore, a
linear relation between the conductivity and the peak FAC density exists,
which implies that the dayside FAC densities are directly controlled by the
amount of solar radiation. Solar elevation does not affect the nightside FAC density. On the dayside a systematic
difference of the footprint latitude between sunlit and dark conditions
emerges. Under dark conditions the auroral region
retreats about 2° equatorward. On the basis of
the above results, we may suggest that the sources of Birkeland
currents on the zdayside behave like a voltage
source, while on the nightside the response is
possibly like a current source.
Copyright
2005 by the American Geophysical Union.
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Magnetotail response to prolonged southward IMF B z
intervals: Loading, unloading, and continuous magnetospheric
dissipation
Tanskanen E. I., J. A. Slavin,
D. H. Fairfield, D. G. Sibeck, J. Gjerloev, T. Mukai, A. Ieda, T. Nagai (2005), Magnetotail
response to prolonged southward IMF B z intervals: Loading, unloading, and
continuous magnetospheric dissipation, J. Geophys. Res., 110, A03216, doi:10.1029/2004JA010561.
2005-03-22
Abstract: The response of the Earth's magnetotail
to prolonged southward interplanetary magnetic field (IMF) has been
determined for the three Geotail magnetotail seasons from November to April, 1999–2002.
We examine the total magnetotail pressure P T,tail = B 2 /2μ 0 + N i kT i
because variations should be similar in this parameter in the lobes and in
the plasma sheet. We found 13 events when IMF B z remained southward for 8
hours or longer and Geotail was located within
the magnetotail farther than 10 R E downstream.
All 13 events were subdivided into separate intervals characterized as (1)
loading, if the tail total pressure increased more than 100%;
(2) unloading, if the total pressure decreased by more than 50%;
and (3) what we term here continuous magnetospheric
dissipation (CMD), if the tail total pressure increased by less than
100% and/or decreased less than 50% during the entire
mode interval. In total, 37 loading, 37 unloading,
and 28 CMD events were found. The plasma sheet magnetic flux transfer rate,
$\phi$ Earth ≈ v x ?
B z, and plasma bulk velocity has been analyzed to determine the steadiness
of the plasma sheet convection. Plasma sheet convection was found to be
highly disturbed and intense plasma flows (BBFs
and FBs) were observed during all convection
states. However, the occurence rate and amplitude
of plasma flows distinguish loading-unloading and continuous dissipation
periods from each other. BBFs seem to be more
numerous (135) but weaker (about 500 km/s) during continuous dissipation
intervals compared with BBFs existing during
unloading mode (61 and 660 km/s). Finally, it was found that CMD-type
convection is more likely when the mean southward IMF B z > −5 nT, while loading-unloading is more likely when IMF B z
< −5 nT.
Copyright
2005 by the American Geophysical Union.
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Multipoint
observations of transient reconnection signatures in the cusp
precipitation: A Cluster-IMAGE detailed case study
Bosqued J. M., et al. (2005), Multipoint observations of
transient reconnection signatures in the cusp precipitation: A
Cluster-IMAGE detailed case study, J. Geophys.
Res., 110, A03219, doi:10.1029/2004JA010621.
2005-03-29
Abstract: This paper uses 90 min of Cluster multipoint data at ∼5 R E altitude together with global dayside imaging data
provided by the IMAGE-SI-12 instrument to analyze the northern cusp crossed
on 14 July 2001, during a period of high solar wind pressure P sw and strongly duskward
interplanetary magnetic field (IMF). Simultaneous observations reveal
intense cusp activity in the postnoon sector,
characterized by multiple, impulsive energy-dispersed ion injections, with
a recurrence time of ∼8–10 min or less.
Most of these transient signatures correspond one to one with repeated P sw enhancements. A multipoint analysis reveals that
field-aligned current sheets associated with ion steps are moving
predominantly westward with a velocity, up to ∼20 km/s, in agreement with a flux tube motion controlled by
magnetic tension forces when IMF B y $\gg$ 0.
These data are used to infer a source region located at ∼7–13 R E from Cluster, that is, on the dusk flank of the
compressed magnetosphere, around 17–18 magnetic local time.
We interpret these very dynamic and transient features as probable
signatures of pulsed magnetic reconnection that is operating in a localized
region of the magnetopause centered in the preferential antiparallel
merging site. Our results suggest that the reconnection rate is not
spontaneously self-varying but may be directly modulated by either upstream
dynamic pressure P sw or changes in the IMF
polarity.
Copyright
2005 by the American Geophysical Union.
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Kp forecast models
Wing S., J. R.
Johnson, J. Jen, C.-I. Meng, D. G. Sibeck, K. Bechtold, J.
Freeman, K. Costello, M. Balikhin, K. Takahashi
(2005), Kp forecast models, J. Geophys. Res., 110, A04203, doi:10.1029/2004JA010500.
2005-04-09
Abstract: Magnetically active times, e.g., Kp
> 5, are notoriously difficult to predict, precisely the times when such
predictions are crucial to the space weather users. Taking advantage of the
routinely available solar wind measurements at Langrangian
point (L1) and nowcast Kps,
Kp forecast models based on neural networks were
developed with the focus on improving the forecast for active times. To
satisfy different needs and operational constraints, three models were
developed: (1) a model that inputs nowcast Kp and solar wind parameters and predicts Kp 1 hour ahead; (2) a model with the same input as model
1 and predicts Kp 4 hour ahead; and (3) a model
that inputs only solar wind parameters and predicts Kp
1 hour ahead (the exact prediction lead time depends on the solar wind
speed and the location of the solar wind monitor). Extensive evaluations of
these models and other major operational Kp
forecast models show that while the new models can predict Kps more accurately for all activities, the most
dramatic improvements occur for moderate and active times. Information
dynamics analysis of Kp suggests that geospace is more dominated by internal dynamics near
solar minimum than near solar maximum, when it is more directly driven by
external inputs, namely solar wind and interplanetary magnetic field
(IMF).
Copyright
2005 by the American Geophysical Union.
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Neutral
composition effects on ionospheric storms at
middle and low latitudes
Liou K., P. T. Newell, B. J. Anderson, L. Zanetti, C.-I. Meng (2005),
Neutral composition effects on ionospheric storms
at middle and low latitudes, J. Geophys. Res.,
110, A05309, doi:10.1029/2004JA010840.
2005-05-20
Abstract: The two-dimensional structure of thermospheric
neutral composition, specifically, the atomic oxygen to molecular nitrogen
column density ratio, [O/N 2], is studied during the 17–24 April 2002
geomagnetic storms to understand the cause of ionospheric
storms in regions equatorward of the auroral oval on an instantaneous large scale. The [O/N
2] ratio is derived from the dayglow emission
ratio of O I 1356
Copyright
2005 by the American Geophysical Union.
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Stagnant
exterior cusp region as viewed by energetic electrons and ions: A
statistical study using Cluster Research with Adaptive Particle Imaging
Detectors (RAPID) data
Zhang H., T. A.
Fritz, Q.-G. Zong, P. W. Daly (2005), Stagnant
exterior cusp region as viewed by energetic electrons and ions: A
statistical study using Cluster Research with Adaptive Particle Imaging
Detectors (RAPID) data, J. Geophys. Res., 110,
A05211, doi:10.1029/2004JA010562.
2005-05-27
Abstract: We present statistical results based on the data set
obtained by Cluster when these spacecraft were in the dayside cusp and
magnetopause. Forty clearest stagnant exterior cusp (SEC) events have been
selected from ∼150 cusp crossings
from 1 January to 30 April 2001 and from 1 March to 30 April 2002. The
identification of the SECs was made on the basis
of the following criteria: high-density plasma (comparable to the sheath
level) and small or stagnant plasma flow (V x < 60 km s −1). We
found that energetic ions are observed in the high-latitude magnetospheric region for 32 SEC crossings (80%) and energetic electrons are observed on 9 of 40
events (22.5%). The SEC is found to lie predominantly within
1000–1300 magnetic local time (MLT); however, there are some cases where
this region extends to both earlier and later MLTs.
Twenty-nine SEC events (72.5%) have been found in association
with depressed magnetic field. The angular difference between the
interplanetary magnetic field (IMF) and local clock angles is a good
criterion for 29 SEC events (72.5%).
The particle spectra are characterized by a power law, and the power law
index is found to be closely related to solar wind velocity. The spectra
seem to be harder for higher solar wind velocity. We also found that the
higher the solar wind velocity, the higher the ion flux
in the SEC region. The magnetic shear angle is the difference between local
B vector and IMF clock angle projected on the plane perpendicular to the
shock normal. The larger the magnetic shear angle, the more turbulent the
magnetic field in the SEC. The turbulence in the SEC region does not affect
the power law index, but it is one of the factors controlling of the SEC
region. Further, there is no clear relationship found between the power law
index and IMF B z, Dst, or the magnetic shear
angle.
Copyright
2005 by the American Geophysical Union.
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Enhanced
solar wind geoeffectiveness after a sudden
increase in dynamic pressure during southward IMF orientation
Boudouridis A., E. Zesta, L. R. Lyons, P. C. Anderson, D. Lummerzheim (2005), Enhanced solar wind geoeffectiveness after a sudden increase in dynamic
pressure during southward IMF orientation, J. Geophys.
Res., 110, A05214, doi:10.1029/2004JA010704.
2005-05-27
Abstract: It is well known that a persistent southward
Interplanetary Magnetic Field (IMF) produces increased geomagnetic
activity. It has recently been shown that a sudden increase in solar wind
pressure results in poleward expansion of the auroral oval and closing of the polar cap over a wide
range of MLTs, and this effect is more pronounced
under southward IMF orientation. We show that southward IMF conditions
combined with high solar wind dynamic pressure immediately after a pressure
front impact lead to enhanced coupling between the solar wind and the
terrestrial magnetosphere, significantly increasing the geoeffectiveness
of the solar wind. We evaluate geoeffectiveness
by the coupling efficiency, defined as the ratio of the cross-polar-cap potential
measured by Defense Meteorological Satellite Program (DMSP) spacecraft to
the cross-magnetospheric potential calculated
using solar wind parameters. We examine changes in the size of the polar
cap and the coupling efficiency for a number of solar wind pressure
enhancements under southward IMF configuration. We confirm the previously
observed closing of the polar cap and show that there is a simultaneous
increase of the coupling efficiency. This increase is measured for all
cases, despite the fact that the magnetosphere is greatly compressed, and
the increase is measured even when the solar wind electric field is
reduced.
Copyright
2005 by the American Geophysical Union.
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Acceleration
and transport of heavy ions at coronal mass ejection-driven shocks
Li G., G. P. Zank, W. K. M. Rice (2005), Acceleration and transport
of heavy ions at coronal mass ejection-driven shocks, J. Geophys. Res., 110, A06104, doi:10.1029/2004JA010600.
2005-06-24
Abstract: It is now widely accepted that large solar energetic
particle (SEP) events are associated with coronal mass ejection
(CME)-driven shocks. Here, particles are often accelerated to approximately
MeV energies (and perhaps up to GeV energies) at shock waves driven by CMEs. In this paper, on the basis of our earlier work,
we present a detailed model which calculates the acceleration of heavy ions
at CME-driven shocks and their subsequent propagation in the interplanetary
medium. The CME-driven shock is followed numerically using the two-dimensional
ZEUS code. At the shock front and upstream of the shock, the coupled system
of streaming protons and stimulated upstream turbulence (assuming the form
of Alfvén waves) is considered and the diffusion
coefficient of the energetic ions and the stimulated wave intensity is
evaluated self-consistently. The particle diffusion coefficient is then
used to determine the maximum momentum of energetic ions. The ion spectra
at the shock front are obtained by adopting the steady-state solution of
the transport equation. Across the shock front, the upstream turbulence is
amplified and the particle diffusion coefficient is further decreased.
Energetic particles in the downstream region convect
with the solar wind, cool adiabatically, and diffuse. These effects are followed
using a shell model. Particles diffuse ahead of the shock front, can escape
and propagate in the interplanetary medium subject to pitch angle
scattering. The transport of these particles is followed using a
Monte-Carlo code. Two shocks, one strong and one weak, are considered. Time
intensity profiles and particle spectra at various times are obtained for
two groups of ions, corresponding to Fe and CNO particles. These results
will be helpful on understanding in situ observations at 1 AU made by spacecraft
such as ACE and Wind.
Copyright
2005 by the American Geophysical Union.
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AE
index variability during corotating fast solar
wind streams
Diego P., M. Storini, M. Parisi, E. G. Cordaro (2005), AE index variability during corotating fast solar wind streams, J. Geophys. Res., 110, A06105, doi:10.1029/2004JA010715.
2005-06-24
Abstract: We examine the AE index variability while 12 corotating fast solar wind streams pass the Earth
during the ascending phase of the ongoing solar activity cycle. We apply
the Discrete Fourier Transform analysis to the associated interplanetary
magnetic field (B) data and AE time series with ∼1 min resolution. Results show noticeable periodicities in the
1–10 hour range. Moreover, the B and AE periodicities in each event are
well correlated. For this reason a direct relationship between
interplanetary Alfvénic waves and AE oscillations
is proposed while those streams pass the Earth.
Copyright
2005 by the American Geophysical Union.
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Computing
the reconnection rate at the Earth's magnetopause using two spacecraft
observations
Fuselier S. A., K. J. Trattner, S. M. Petrinec, C. J. Owen, H. R
2005-06-24
Abstract: A new multispacecraft technique
is introduced which, under some restrictive assumptions and conditions,
provides a snapshot of the reconnection inflow velocity into the
magnetosphere and an estimate of the distance from the spacecraft to the
reconnection site. The two quantities are not obtained independent of one
another and additional, independent information is needed to separate them.
This new technique is applied to Cluster spacecraft observations at the
Earth's magnetopause. Additional Cluster observations and observations from
the IMAGE spacecraft are used as independent information to provide an
estimate of the distance from the spacecraft to the reconnection site for
the event. From this distance estimate and the new multispacecraft
technique, it is concluded that component reconnection was probably
occurring at the magnetopause and that the local inflow velocity was
significantly less than 0.1 V A.
Copyright
2005 by the American Geophysical Union.
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On
the relationships between double-onset substorm, pseudobreakup, and IMF variation: The 4 September 1999
event
Cheng C.-C., C.
T. Russell, G. D. Reeves, M. Connors, M. B. Moldwin
(2005), On the relationships between double-onset substorm,
pseudobreakup, and IMF variation: The 4 September
1999 event, J. Geophys. Res., 110, A07201, doi:10.1029/2004JA010778.
2005-07-02
Abstract: The relationships between double-onset substorm,
pseudobreakup, and IMF variation were
investigated with magnetic, auroral, and particle
observations from space to the ground during 0200–0600 UT on 4 September
1999. There were five consecutive bursts of Pi2 pulsations on the ground
during the time of interest. The onset time of ground Pi2s maps to the same
variation sequence in the IMF structure seen propagating to the Earth in
multiple satellite observations in the upstream region. The comparison of auroral and energetic particle data with IMF
observations shows that a sequence of two double-onset substorms
intervened by a pseudobreakup appears in two
distinct cycles of southward IMF followed by a northward interval. For the
first substorm, the first onset begins when the B
y magnitude declines after the IMF turns southward for about 90 min, and
the second onset occurs after northward turning of the IMF accompanied by
an increasing B y magnitude. The pseudobreakup
appears while the IMF turns southward and the B y magnitude slightly
decreases. For the second substorm, the first
onset commences while the IMF remains southward with a steady B y magnitude, and the second onset occurs after the IMF
becomes strongly northward and the B y magnitude decreases instead. These
observations can be explained with the two-neutral-point model. The first
onset occurs when the IMF turns southward. Reconnection at the near-Earth
neutral point first begins on closed field lines within the plasma sheet,
and the second onset occurs when the IMF turns northward and reconnection
at the distant neutral point ceases and reconnection at the near-Earth neutral
point may reach the open flux of the tail lobes. In addition, a decrease in
the B y magnitude may help reduce magnetotail
convection and release all the built-up flux to allow the onset to commence
after northward turning of the IMF. If the IMF remains southward, the
reduction of magnetotail convection due to a
decreasing B y would lead to a pseudobreakup
instead. In contrast, an increasing B y magnitude would increase magnetotail convection and weaken magnetospheric
substorm after the IMF turns northward.
Consequently, for the occurrence of double-onset substorms
and pseudobreakups, not only the first onset
begins spontaneously during steady southward IMF and the second onset
appears after northward turning of the IMF but the B y change also affects magnetotail convection which may evoke (or abate) the substorm-related activation while the IMF turns
southward (or northward).
Copyright
2005 by the American Geophysical Union.
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Are
sawtooth oscillations of energetic plasma
particle fluxes caused by periodic substorms or
driven by solar wind pressure enhancements?
Huang C.-S., G.
D. Reeves, G. Le, K. Yumoto (2005), Are sawtooth oscillations of energetic plasma particle
fluxes caused by periodic substorms or driven by
solar wind pressure enhancements?, J. Geophys.
Res., 110, A07207, doi:10.1029/2005JA011018.
2005-07-07
Abstract: Energetic electron and proton fluxes measured by
geosynchronous satellites often show sawtooth-like
variations during magnetic storms. We examine whether the sawtooth oscillations and relevant magnetospheric-ionospheric
disturbances are caused by periodic substorms or
driven by a series of enhancements in the solar wind pressure. We show that
there are significant differences between periodic substorms
and solar wind-induced variations. The energetic fluxes at geosynchronous
orbit may increase by orders of magnitude after each onset of periodic substorms and by 10–50% in response to a
large solar wind pressure impulse. The sudden increases of the energetic
fluxes during periodic substorms show significant
time delays of 30–50 min at different longitudes/local times, indicating
that the fluxes are injected on the nightside and
then drift to the dayside. In contrast, the small flux increases caused by
solar wind pressure enhancements occur almost simultaneously at all local
times. The periodic substorms always have a
strong spectrum peak at 2–3 hours, no matter whether the solar wind
pressure and/or IMF have similar spectrum peaks. The nightside
magnetospheric magnetic elevation angle shows a
large (30–60
Copyright
2005 by the American Geophysical Union.
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Local
time distribution of low and middle latitude ground magnetic disturbances
at sawtooth injections of 18–19 April 2002
Kitamura K., H.
Kawano, S. Ohtani, A. Yoshikawa, K. Yumoto (2005), Local time distribution of low and
middle latitude ground magnetic disturbances at sawtooth
injections of 18–19 April 2002, J. Geophys. Res.,
110, A07208, doi:10.1029/2004JA010734.
2005-07-08
Abstract: During a magnetic storm of 18 April 2002, quasi-periodic
variations of the low-energy electron flux were observed by the LANL
satellites at geosynchronous orbit; this phenomenon has been called the “sawtooth event.” During this event, on the ground,
magnetic bays and Pi 2 pulsations took place corresponding to each
enhancement of the particle flux, and they had features typical to usual substorms. However, unlike typical substorms,
the ACE satellite observed no apparent northward turnings of the IMF
corresponding to the sawtooth event. In this
study, we used ground magnetic data from middle- and low-latitude stations
which are distributed widely in the longitudinal direction, selected from
the CPMN (Circum-Pan Pacific Magnetometer Network) and INTERMAGNET stations
and compared the magnetic variations during the sawtooth
event with that of the typical substorm (Lester
et al., 1984). We found that the local time distribution of the
polarization axis of the Pi 2 pulsations show a good agreement with that
for a typical substorm, except that the local
time width of the expected current wedge was 12 hours. On the other hand,
the H component is predominant in the amplitude of the magnetic bay on the
ground; the distribution of the H component also suggests a 12-hour-wide current
wedge, which did not develop much in time. From these features, it is
suggested that a current wedge was formed during this sawtooth
event, and it generated the Pi 2 pulsations on the ground. However, the
local time width of the current wedges is much wider than typical substorms, and its uniqueness causes the ground
features different from typical substorm-associated
magnetic variations on the ground.
Copyright
2005 by the American Geophysical Union.
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Occurrence
statistics of cold, streaming ions in the near-Earth magnetotail:
Survey of Polar-TIDE observations
Liemohn M. W., T. E. Moore, P. D. Craven, W.
Maddox, A. F. Nagy, J. U. Kozyra
(2005), Occurrence statistics of cold, streaming
ions in the near-Earth magnetotail: Survey of Polar-TIDE
observations, J. Geophys. Res., 110, A07211, doi:10.1029/2004JA010801.
2005-07-09
Abstract: Results are presented from a survey of cold ion
observations in the near-Earth magnetotail using
data from the Polar Thermal Ion Dynamics Experiment (TIDE). During the
interval from July to December of 2001, Polar had its apogee (∼9.5 R E) near the equatorial plane in the tail region of the
magnetosphere. It is shown that a lobal wind is
ubiquitous in the inner tail, with low-energy (<300 eV)
ions streaming from the ionosphere downtail.
These lobal winds often pass through the plasma
sheet, forming bidirectional streams, in addition to the unidirectional
beams seen at higher magnetic latitudes. The observance of bidirectional
streams is inversely, although weakly, correlated with geomagnetic
activity. Bidirectional streams are interpreted as indicating the minimum
size of the closed flux tube region. The reduced frequency of bidirectional
streams with activity level times is consistent with the thinning of the
plasma sheet during these times. It is inferred from the universality of these
observations during Polar's passage through the
inner tail region that the ionosphere is a continuous supplier of plasma to
the near-Earth magnetosphere. The high occurrence rate of these streams
means that during geomagnetic disturbances, it is not necessary to wait for
outflow and magnetospheric circulation in order
to supply the inner magnetosphere with ionospheric
ions; these cold streams are an immediately available supply of ionospheric-origin particles.
Copyright
2005 by the American Geophysical Union.
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Storm-time
field-aligned currents on the nightside inferred
from ground-based magnetic data at midlatitudes:
Relationships with the interplanetary magnetic field and substorms
Nakano S., T. Iyemori (2005), Storm-time field-aligned currents on
the nightside inferred from ground-based magnetic
data at midlatitudes: Relationships with the
interplanetary magnetic field and substorms, J. Geophys. Res., 110, A07216, doi:10.1029/2004JA010737.
2005-07-15
Abstract: On the basis of analysis of east-west geomagnetic
disturbance fields at midlatitudes, we
investigated the characteristics of temporal variations of field-aligned
currents on the nightside during geomagnetic
storms. The results indicate that upward field-aligned currents develop on
the nightside, especially in the postmidnight, when the interplanetary magnetic field
(IMF) is directed southward. This suggests that the upward field-aligned
currents are principally associated with the convection electric field. It
is also found that the upward field-aligned currents in the postmidnight can be intensified at substorm
expansion, while they principally depend on the southward component of the
IMF. The intensification of the upward currents is regarded as a different
physical process from the formation of a substorm
current wedge at a substorm expansion. We discuss
some possible effects of the IMF and substorms on
the generation of the upward currents on the nightside,
especially in the postmidnight.
Copyright
2005 by the American Geophysical Union.
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Toward
a synthesis of equatorial spread F onset and suppression during geomagnetic
storms
Martinis C. R.,
M. J. Mendillo, J. Aarons (2005), Toward a
synthesis of equatorial spread F onset and suppression during geomagnetic
storms, J. Geophys. Res., 110, A07306, doi:10.1029/2003JA010362.
2005-07-22
Abstract: We present initial steps toward unifying our understanding
of storm time equatorial spread F (ESF) by searching for the common
elements in past case studies and statistical occurrence patterns. We show
that the development (or inhibition) of equatorial irregularities during
magnetically active periods can be understood using the AE -parameterized Fejer-Scherliess model for disturbance vertical drifts
versus storm time and local time. This model takes into account the
different sources of perturbation electric fields (magnetospheric
and ionospheric dynamos) that ultimately drive
the equatorial vertical drifts, showing prompt and delayed effects in the premidnight sector (where both generation and
suppression can occur), as well as in the postmidnight
period where generation dominates. The postsunset
period exhibits the greatest variability for storm time ESF versus
longitude, and thus we demonstrate the Fejer-Scherliess
model's applicability in a test case (6 April 2000) that had an AE pattern
compatible with their parameterization scheme. The model successfully
accounts for the pronounced longitude confinement in the observed postsunset ESF patterns. Finally, we move beyond the
empirically derived relationships between geomagnetic indices and the
occurrence of ESF (Aarons, 1991) into a framework of true solar-terrestrial
parameters that drive such effects. Additional case studies taken from the
published literature are then used to show a consistent linkage between postsunset ESF onset and the interplanetary electric
field (IEF) E sw. While AE, Dst,
Kp and Dst / dt indices were used in earlier studies to determine
the dusk-longitude sector of disturbance electric fields, here we attribute
to the IEF the main role in the determination of this longitude
sector.
Copyright
2005 by the American Geophysical Union.
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A
statistical analysis of the assimilative mapping of ionospheric
electrodynamics auroral specification
Kihn E. A., A. J. Ridley (2005), A statistical analysis of
the assimilative mapping of ionospheric
electrodynamics auroral specification, J. Geophys. Res., 110, A07305, doi:10.1029/2003JA010371.
2005-07-22
Abstract: The assimilative mapping of ionospheric
electrodynamics (AMIE) technique utilizes a wide range of electrodynamics
measurements to determine high-latitude maps of the electric potential,
electron particle precipitation (average energy and total energy flux), and
ionospheric conductance (Hall and Pedersen). AMIE
does this by conducting a least squares fit to the
difference between the data and a background model. This fit is then added
to the background model. This allows for a very stable technique with even
minimal amounts of data. The background models are typically statistical
models that are driven by the solar wind and interplanetary magnetic field
or the hemispheric power index. This study presents results of a
statistical validation of the AMIE conductance and particle precipitation calculations
and quantifies how using ground magnetometer derived measurements improves
upon the result obtained using only a background statistical model.
Specifically, we compare AMIE using the Fuller-Rowell and Evans (1987)
model of particle precipitation and ionospheric conductances to DMSP particle precipitation
measurements during the period from May to November 1998. The conductances are derived from the particle
precipitation using the Robinson et al. (1987) formulation. The
Fuller-Rowell and Evans (1987) results show low (39–21% with
increasing AE) energy flux integrals with respect to DMSP auroral passes and differences in mean electron
energies. The AMIE runs, in which ground-based magnetometers were used to
modify the particle precipitation using the formulation by Ahn et al. (1983) and Ahn et
al. (1998), show significant improvement in correlation to the
observational data. We show that it more accurately predicts the particle
precipitation than when using only the background model, especially in the
1800–0300 MLT nightside sectors where solar
conductance is not significant. In addition, the AMIE results show a clear
increase in accuracy with increasing number of magnetometers in a
sector.
Copyright
2005 by the American Geophysical Union.
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A
new interpretation of Weimer et al.'s solar wind propagation delay
technique
Bargatze L. F., R. L. McPherron, J. Minamora, D. Weimer (2005), A new interpretation of
Weimer et al.'s solar wind propagation delay technique, J. Geophys. Res., 110, A07105, doi:10.1029/2004JA010902.
2005-07-27
Abstract: We present an evaluation of the Weimer et al. (2003)
scheme designed to model interplanetary magnetic field (IMF) phase front
propagation in the solar wind. The new method is based on the fact that IMF
fluctuations tend to be rotations contained within planes. Weimer et al.
(2003) report that phase front orientations can be found via minimum
variance analysis (MVA) with planar normals
defined by the minimum variance direction. The phase plane tilt angle
results they present appear to be accurate as they vary in a similar
fashion to those found utilizing phase front coplanarity
analysis using multipoint interplanetary observations (Weimer et al.,
2002). Here we report on an attempt to reproduce their results, an effort
that failed since Weimer et al. (2003) adopted a nonstandard form of the
equation used to calculate the magnetic field variance matrix that composes
the basis of MVA. Use of the modified variance matrix forces a reevaluation
of the physics underlying their new propagation model. The revised
interpretation suggests that phase plane orientations are organized in a
coordinate system whose axes are defined by the mean IMF direction and the
minimum and maximum perturbation directions perpendicular to the mean field
vector. The phase plane normal is found to be the minimum perturbation
direction in this coordinate system. Given that the new technique appears
to improve the accuracy of estimating solar wind propagation delays and
that it requires IMF data from only one interplanetary monitor, testing it
as a space weather forecasting tool is clearly motivated.
Copyright
2005 by the American Geophysical Union.
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Indirect
estimation of the solar wind conditions in 29–31 October 2003
Dmitriev A. V., J.-K. Chao, A. V. Suvarova,
K. Ackerson, K. Ishisaka, Y. Kasaba,
H. Kojima, H. Matsumoto (2005), Indirect estimation of the solar wind
conditions in 29–31 October 2003, J. Geophys.
Res., 110, A09S02, doi:10.1029/2004JA010806.
2005-07-28
Abstract: A comparative analysis of the solar wind conditions was
performed for extremely disturbed event on 29–31 October 2003. It was found
that the ACE and Geotail upstream monitors
provided very similar data on the IMF but that plasma measurements in the
SOHO CELIAS/MTOF, ACE SWEPAM, IMP 8 MIT, and Geotail
CPI experiments are very different. The solar wind velocity was indirectly
estimated using the time lag for propagation of such solar wind structures
as interplanetary shock, Alfven waves, rotational, and tangential
discontinuities from point L1 to the Earth. We found the best
correspondence of the estimated velocity was with the ACE SWEPAM data,
which displayed very fast (up to 2000 km/s) solar wind, while the IMP 8, Geotail, and SOHO
plasma instruments are unable to measure such a fast solar wind stream.
Application of the magnetopause models to a data set of numerous
geosynchronous magnetopause crossings observed by GOES and LANL satellites
enabled estimation of the solar wind dynamic pressure. In general the
estimated pressure and density are in agreement with the solar wind plasma
parameters provided by the ACE SWEPAM experiment. An estimation of the
solar wind density corresponds very well to the electron density restored
from the Geotail PWI data. However, during
1600–1800 UT on 29 October, 1700–1800 UT on 30 October,
and 0000–0400 UT on 31 October, the estimated solar wind pressure and
density are several times larger than provided by the Geotail
PWI and ACE SWEPAM. A large helium abundance is
considered as a possible reason for the solar wind pressure underestimation
in the first case. The understated solar wind density on 30–31 October
might be explained by errors in the method for restoring of the plasma data
in fast solar wind (>900 km/s) accompanied with intensive fluxes (few
tens of particles per cm 2 s sr) of high-energy
(>30 MeV) solar energetic protons.
Copyright
2005 by the American Geophysical Union.
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Comparison
of intense nightside shock-induced precipitation
and substorm activity
Meurant M., J.-C. Gérard, C. Blockx, V. Coumans, B.
Hubert, M. Connors, L. R. Lyons, E. Donovan (2005), Comparison of intense nightside shock-induced precipitation and substorm activity, J. Geophys.
Res., 110, A07228, doi:10.1029/2004JA010916.
2005-07-28
Abstract: Sudden variations of the solar wind dynamic pressure
frequently induce dayside enhancements of auroral
activity with features such as high-latitude arcs, low-latitude proton
flashes, and enhancement of auroral precipitation
propagating dawnward and duskward
from noon to the night sector. In some cases, these shocks also induce
enhanced activity during which the power precipitated into the night sector
may reach values as high as observed during substorms.
Several studies have shown that the triggering of nightside-enhanced
precipitation is more likely during periods of southward interplanetary
magnetic field (IMF) components. Early works showed that substorm-like activity is not frequent after a shock
and suggested that shocks may not be considered as substorm
triggers. We examine up to what point substorm-like
nightside activity triggered by a shock is
comparable to an isolated substorm. For this
purpose, we analyze three events morphologically similar to substorms and occurring within less than 20 min after
the arrival of a pressure pulse on the front of the magnetosphere.
Different features of these events such as the mean energy of precipitated
electrons, the latitudinal motion of boundaries before and after onset, and
the power precipitated into the nightside sector
are compared with isolated substorms. We conclude
that the characteristics of shock-induced substorms
appear very similar to those of isolated substorms.
Shocks are able to trigger substorms when they
hit an unstable magnetosphere. The interpretation is that the perturbation
due to the shock induces a substorm by closure of
the plasma sheet magnetic field. For the events presented in this study,
the instability result from a period of southward IMF or stretching of the
magnetic tail induced by a previous shock.
Copyright
2005 by the American Geophysical Union.
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Magnetospheric
field-line resonances: Ground-based observations and modeling
Rankin R., K. Kabin, J. Y. Lu, I. R. Mann, R. Marchand,
I. J. Rae, V. T. Tikhonchuk, E. F. Donovan
(2005), Magnetospheric field-line resonances: Ground-based observations and
modeling, J. Geophys. Res., 110, A10S09, doi:10.1029/2004JA010919.
2005-07-28
Abstract: We present theory and ground-based observations of field-line
resonances (FLRs) excited in Earth's
magnetosphere. Three FLR observations are reported, which correspond to
large-scale standing shear Alfv
Copyright
2005 by the American Geophysical Union.
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Resolving
the enigmatic solar wind disappearance event of 11 May 1999
Janardhan P., K. Fujiki, M.
Kojima, M. Tokumaru, K. Hakamada
(2005), Resolving the enigmatic solar wind disappearance event of 11 May
1999, J. Geophys. Res., 110, A08101, doi:10.1029/2004JA010535.
2005-08-03
Abstract: On 11 and 12 May 1999, the Earth was engulfed by an
unusually low-density (<1 cm −3) and low-velocity (<350 km s
−1) solar wind for a period of over 1 day. Extensive studies of this
unusual event that occurred during Carrington rotation 1949 (CR1949), using
both ground-based and space-based in situ observations, have not as yet been
able to identify the cause or the solar source of this event. Using solar
wind velocity measurements from the four-station IPS observatory of the
Solar-Terrestrial Environment Laboratory (STEL), Toyokawa, Japan, we investigate the
structure of the solar wind in May 1999 during CR1949. IPS observations
from STEL were used to make tomographic velocity
maps to identify and delineate the extent and morphology of the stable
solar wind flows during CR1949 in the vicinity of the Earth. Combined with
in situ measurements of the interplanetary magnetic field (IMF), potential
field computations of the solar magnetic fields in the period, and HeI 10830
Copyright
2005 by the American Geophysical Union.
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Southern
Hemisphere ionosphere and plasmasphere response
to the interplanetary shock event of 29–31 October 2003
Yizengaw E., M. B. Moldwin, P. L.
Dyson, T. J. Immel (2005), Southern Hemisphere
ionosphere and plasmasphere response to the
interplanetary shock event of 29–31 October 2003, J. Geophys.
Res., 110, A09S30, doi:10.1029/2004JA010920.
2005-08-10
Abstract: We analyze the effects on the Southern Hemisphere
ionosphere and plasmasphere due to the 29–31
October 2003 geomagnetic storms (the so-called series of Halloween storms).
Solar wind data from ACE and ionospheric data
from the GPS (Global Position System) ground and LEO (Low Earth Orbit)
receivers, the TOPEX/Poseidon altimeter, the IMAGE FUV camera, and the DMSP
drift meter are used to understand the ionospheric
dynamics as a function of the storm phase. The detailed structure of the
ionosphere has been obtained using tomographic
reconstruction applied to data from both ground- and space-based GPS
receivers. The tomographic approach using LEO
observations of signals received from GPS satellites above the LEO's horizon allows us to investigate the topside ionospheric and plasmaspheric
density distribution in more detail than can be obtained using ground-based
GPS receivers. This is because with ground-based receivers, the higher
topside ionosphere and plasmasphere contribute
only a small fraction to the total electron content (TEC) and so the
measurements are dominated by the ionospheric
structure at the F 2 peak. In contrast, the Australian LEO satellite, FedSat, which has been used for this study, orbits at
800 km altitude, well above the F 2 peak and hence the TEC measured is
primarily due to the upper topside ionosphere and plasmasphere.
This paper presents the tomographically
reconstructed topside ionosphere and plasmasphere
electron density distributions using LEO observations. The temporal and
regional maps of TEC and the IMAGE FUV data show that the storm that
commenced on 29 October dramatically decreased the plasma density in the
Southern Hemisphere middle and high latitudes. The region remained depleted
of plasma for more than 24 hours until 31 October, when the second severe
storm began. TOPEX/Poseidon data shows a daytime localized density
enhancement occurred above the middle of the Pacific
Ocean. These results show large interhemispheric
and longitudinally narrow storm-time structure in the ionosphere and
topside ionosphere/plasmasphere.
Copyright
2005 by the American Geophysical Union.
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Low-frequency
plasma oscillations at Mars during the October 2003 solar storm
Espley J. R., P. A. Cloutier, D. H.
Crider, D. A. Brain, M. H. Acuña (2005),
Low-frequency plasma oscillations at Mars during the October 2003 solar
storm, J. Geophys. Res., 110, A09S33, doi:10.1029/2004JA010935.
2005-08-11
Abstract: The powerful x-class flare which occurred on the Sun on 28
October 2003 had important effects on plasma environments throughout the
solar system. We present here observations of the effects at Mars from the
Mars Global Surveyor (MGS) Magnetometer/Electron Reflectometer
experiment. In particular we focus on the changes in the nature of the
magnetic oscillations observed at an altitude of 400 km (MGS's current orbital altitude) during the passage of
the solar storm. We find that strong, regular oscillations are observed in
both the B $\parallel$ and B $\perp$ components
of the magnetic field at all solar zenith angles. We emphasize in
particular the powerful, coherent oscillations observed in the normally
quiet nightside region. These oscillations carry
power at the proton gyrofrequency and at and
below the oxygen gyrofrequency. This implies that
ions of planetary origin are interacting with the solar wind plasma and
raises the possibility that significant atmospheric loss may occur during
the passage of large solar storms at Mars.
Copyright
2005 by the American Geophysical Union.
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Near-relativistic
electron emission following the 28 October 2003 X17 flare
Simnett G. M. (2005), Near-relativistic electron emission
following the 28 October 2003 X17 flare, J. Geophys.
Res., 110, A09S01, doi:10.1029/2004JA010789.
2005-08-13
Abstract: The 28 October 2003 solar flare event was one of the
largest electron events above 50 keV of the
current solar cycle. The event was associated with a major flare, at least
one fast coronal mass ejection (CME), and a prominence eruption. The
evolution of the electron spectrum for this event enables us to resolve
three, or possibly four, separate electron sources. The source associated
with the passage of a fast CME through the corona lasts about half an hour,
has a very soft spectrum, and appears at 1 AU as a highly anisotropic beam.
The most intense source has a weak outward anisotropy, lasts 2 days before
starting a slow decay, and has a hard spectrum. The event is at its most
intense around the arrival of the shock which is ahead of the CME, and this
is also when the electron spectrum is hardest. One possible interpretation
to explain the spectral and angular distribution properties of the
electrons from this event is discussed.
Copyright
2005 by the American Geophysical Union.
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Ionospheric signatures of plasma injections in the cusp
triggered by solar wind pressure pulses
Cerisier J.-C., A. Marchaudon, J.-M. Bosqued, K. McWilliams, H. U. Frey, M. Bouhram, H. Laakso, M. Dunlop,
M. Förster, A. Fazakerley
(2005), Ionospheric signatures of plasma
injections in the cusp triggered by solar wind pressure pulses, J. Geophys. Res., 110, A08204, doi:10.1029/2004JA010962.
2005-08-18
Abstract: We describe coordinated observations made on 14 July 2001
simultaneously in the midaltitude cusp by Cluster
and at the cusp's ionospheric magnetic footprint
by Super Dual Auroral Radar Network (SuperDARN) and Imager for Magnetopause-to-Aurora Global
Exploration (IMAGE) during a period of three successive solar wind dynamic
pressure pulses. In association with each of these pulses, Cluster observes
plasma injections while auroral images from the
IMAGE spacecraft show enhanced precipitation in the cusp. Following these
plasma injections, channels of fast convection flows are observed in the
ionosphere by the SuperDARN radars. On the basis
of the spatial and temporal relationships between these various signatures,
we analyze the response of the dayside magnetosphere and ionosphere to the
pressure pulses as follows: (1) the solar wind dynamic pressure pulses are
the drivers of plasma injections from the magnetosheath
into the cusp; (2) the ionospheric convection
bursts start shortly after the auroral
intensifications and their duration is much longer (10 min versus 4–6 min
for the auroral intensifications); (3) the
convection bursts occur on the poleward side of
the cusp precipitation; and (4) the Alfv
Copyright
2005 by the American Geophysical Union.
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Mars
Global Surveyor observations of the Halloween 2003 solar superstorm's encounter with Mars
Crider D. H.,
J. Espley, D. A. Brain, D. L. Mitchell, J. E. P. Connerney, M. H. Acu
2005-08-25
Abstract: Like at Earth, disturbances from solar storms affect the
space environment as they encounter Mars. The effects of the 28 October
2003 solar superstorm were among the greatest
observed by the Mars Global Surveyor spacecraft at Mars to date. The
disturbance, defined by an increase in incident solar wind pressure,
encountered Mars on 30 October 2003 and persisted for 43 hours. We present
the effects of the passage of this high-pressure disturbance and compare
the modified Martian space environment to more quiescent times. We find
that the horizontal component of magnetic field is increased on the
dayside. In addition, the solar wind interaction region is compressed
during the disturbance. The solar wind flow has access to lower altitudes
than typical, which likely increases mass loss from the Martian atmosphere.
Regions of opened magnetic field lines can be closed at 400 km due to the
compression of minimagnetospheres, thus altering
locations where ionospheric plasma is protected
from solar wind scavenging at 400 km altitude.
Copyright
2005 by the American Geophysical Union.
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Overwhelming
O + contribution to the plasma sheet energy density during the October 2003
superstorm: Geotail/EPIC
and IMAGE/LENA observations
Nosé M., S. Taguchi, K. Hosokawa, S. P. Christon,
R. W. McEntire, T. E. Moore, M. R. Collier
(2005), Overwhelming O + contribution to the plasma sheet energy density
during the October 2003 superstorm: Geotail/EPIC and IMAGE/LENA observations, J. Geophys. Res., 110, A09S24, doi:10.1029/2004JA010930.
2005-08-25
Abstract: We studied dynamics of O + ions during the superstorm that occurred on 29–31 October 2003, using
energetic (9–210 keV/ e) ion flux data obtained
by the energetic particle and ion composition (EPIC) instrument on board
the Geotail satellite and neutral atom data in
the energy range of 10 eV to a few keV acquired by the low-energy neutral atom (LENA)
imager on board the Imager for Magnetopause-to-Aurora Global Exploration
(IMAGE) satellite. Since the low-energy neutral atoms are created from the outflowing ionospheric ions
by the charge exchange process, we could examine variations of ionospheric ion outflow with the IMAGE/LENA data. In
the near-Earth plasma sheet of X GSM ∼ −6 R E to
−8.5 R E, we found that the H + energy density showed no distinctive
differences between the superstorm and quiet
intervals (1–10 keV cm −3), while the O +
energy density increased from 0.05–3 keV cm
−3 during the quiet intervals to ∼100 keV cm −3 during the superstorm.
The O + /H + energy density ratio reached 10–20 near the storm maximum,
which is the largest ratio in the near-Earth plasma sheet ever observed by Geotail, indicating more than 90% of O + in
the total energy density. We argued that such extreme increase of the O +
/H + energy density ratio during the October 2003 superstorm
was due to mass-dependent acceleration of ions by storm-time substorms as well as an additional supply of O + ions
from the ionosphere to the plasma sheet. We compared the ion composition
between the ring current and the near-Earth plasma sheet reported by
previous studies and found that they are rather similar. On the basis of
the similarity, we estimated that the ring current had the O + /H + energy
density ratio as large as 10–20 for the October 2003 superstorm.
Copyright
2005 by the American Geophysical Union.
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Global
auroral responses to abrupt solar wind changes:
Dynamic pressure, substorm, and null events
Lyons L. R.,
D.-Y. Lee, C.-P. Wang, S. B. Mende (2005), Global
auroral responses to abrupt solar wind changes:
Dynamic pressure, substorm, and null events, J. Geophys. Res., 110, A08208, doi:10.1029/2005JA011089.
2005-08-25
Abstract: Global auroral images are used
to investigate how specific types of solar wind change relate to the
resulting type of auroral-region disturbance,
with the goal of determining fundamental response types. For not strongly
southward IMF conditions (B z $\gtrsim$ −5 nT), we find that IMF changes that are expected to
reduce the convection electric field after $\gtrsim$
30 min of negative IMF B z cause typical substorms,
where expansion phase auroral activity initiates
within the expected location of the Harang
electric field reversal and expands in ∼10 min to cover ∼5 hours of MLT. For not strongly southward IMF conditions,
solar wind dynamic pressure (P dyn) enhancements
compress the entire magnetosphere, leading to a global auroral
enhancement with no evidence for substorm
bulge-region aurora or current wedge formation. Following prolonged
strongly southward IMF (B z $\lesssim$ −8 nT), an IMF change leading to convection electric field
reduction gives a substorm disturbance that is
not much different from substorms for less
strongly southward IMF conditions, other than the expansion phase auroral bulge region seems to expand somewhat more in
azimuth. However, under steady, strongly southward IMF conditions, a P dyn enhancement is found to cause both compressive auroral brightening away from the bulge region and a Harang-region substorm auroral brightening. These two auroral
enhancements merge together, leading to a very broad auroral
enhancement covering ∼10–15 hours of MLT.
Both current wedge formation and compressive energization
in the inner plasma sheet apparently occur for these events. We also find
that interplay of effects from a simultaneous IMF and P dyn
change can prevent the occurrence of a substorm,
leading to what we refer to as null events. Finally, we apply the plasma
sheet continuity equation to the IMF and pressure driven substorm responses and the null events. This
application suggests that solar wind changes cause substorm
onset only if the changes lead to a reduction in the strength of convection
within the inner plasma sheet.
Copyright
2005 by the American Geophysical Union.
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Geosynchronous
magnetopause crossings on 29–31 October 2003
Dmitriev A., J.-K. Chao, M. Thomsen, A. Suvorova
(2005), Geosynchronous magnetopause crossings on 29–31 October 2003, J. Geophys. Res., 110, A08209, doi:10.1029/2004JA010582.
2005-08-25
Abstract: On 29–31 October 2003, numerous geosynchronous
magnetopause crossings (GMCs) were identified
using magnetic field data from two GOES satellites and plasma data from
four Los Alamos National Laboratory (LANL) satellites. We can distinguish
four long-lasting intervals, when geosynchronous satellites observed GMCs in a wide range of local time: at ∼0600–0900 UT 29 October; from ∼1000 UT 29 October
to 0400 UT 30 October; from ∼1700 UT 30 October
to ∼0800 UT 31 October, and at ∼1100–1300 UT 31 October. During a part of those intervals the GMCs occurred in the dawn and dusk sectors under
northward interplanetary magnetic field (IMF) that indicates to magnetospheric compression by extremely high solar wind
pressure. We found that at 0400–1000 UT 31 October the compression was
accompanied with large-amplitude Pc5 pulsation, which can be attributed to
global magnetospheric mode (cavity resonance).
Multiple GMCs were revealed for the time interval
of Pc5 pulsation occasion. An amplitude of the
magnetopause oscillation in noon sector was estimated of about 0.26∼0.6 R E. An application of the magnetopause models enabled us
studying the magnetopause dawn–dusk asymmetry, which was revealed on the
main phase and in maximum of two great geomagnetic storms on 29 and 30
October. We shown that the asymmetry can be formally
represented as a shifting of the dayside magnetopause toward the dusk on
average distance of 0.2∼0.3 R E. Besides, in
some cases the asymmetry was larger and required a shifting of about 0.4 R
E. It was shown that the magnitude of the dawn–dusk asymmetry is related to
the internal geomagnetic disturbances rather than to the external
conditions in the IMF.
Copyright
2005 by the American Geophysical Union.
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Undulations
on the equatorward edge of the diffuse proton
aurora: TIMED/GUVI observations
Zhang Y., L. J.
Paxton, D. Morrison, A. T. Y. Lui, H. Kil, B. Wolven, C.-I. Meng, A. B. Christensen (2005), Undulations on the equatorward edge of the diffuse proton aurora:
TIMED/GUVI observations, J. Geophys. Res., 110,
A08211, doi:10.1029/2004JA010668.
2005-08-25
Abstract: Undulations on the equatorward
edge of the diffuse proton aurora have been identified by using TIMED/GUVI auroral images in the far ultraviolet wavelengths.
While undulations have been previously reported on the duskside
(Lui et al., 1982), GUVI observations show the
undulation also occurs in the dayside, nightside,
and morningside. The GUVI proton auroral images provide direct optical evidence that the
undulations occur in the proton aurora. It is also the first detection of
the undulation in the dayside indicating strong convection shear in the
region. The undulation in the nightside, a wavy
structure in the whole diffuse proton aurora, is significantly different
from those in the duskside and dayside. While
almost all of the undulation events are observed during magnetic storms (Dst < −60 nT), one
exceptional case shows undulation in the dayside with Dst
= 30 nT. However, the case is associated with a
large solar wind speed (650 km/s) and a high
dynamic pressure (14 nPa). Coincident DMSP SSIES
observations suggest that both large ion drift velocity (>1000 m/s) and
strong velocity shear (>0.1 s −1) within the diffuse aurora oval
are necessary conditions for the undulation to occur. The SSIES data also
indicate the areas with large ion drift velocity and shear move to higher
latitudes in the MLT sectors toward midnight. This may explain why the
undulation is rarely detected in the nightside.
Copyright
2005 by the American Geophysical Union.
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Dependencies
of high-latitude plasma convection: Consideration of interplanetary
magnetic field, seasonal, and universal time factors in statistical
patterns
Ruohoniemi J. M., R. A. Greenwald (2005), Dependencies
of high-latitude plasma convection: Consideration of interplanetary
magnetic field, seasonal, and universal time factors in statistical
patterns, J. Geophys. Res., 110, A09204, doi:10.1029/2004JA010815.
2005-09-01
Abstract: The database of the nine radars of the Super Dual Auroral Radar Network (SuperDARN)
in the northern hemisphere has been analyzed for information on factors
that influence the convection of plasma in the high-latitude ionosphere.
The velocity measurements were collected over the period 1998–2002. The
data were first used to derive a new statistical model of convection that
improves upon the earlier one-radar model of Ruohoniemi
and Greenwald (1996) in its specification of the dependence of the
convection pattern on the magnitude and direction of the IMF in the GSM Y-Z
plane. We then derived average patterns for secondary sortings
by season, year, and radar. Such dependencies as emerged were most clearly
seen by contrasting the results for B y + and B y −. The seasonal
effect in the convection pattern is found to have similarities to that of
the sign of B y. In particular, the combination of B y +/summer (B y
−/winter) reinforces the tendency of the B y sign factor to sculpt
the dusk and dawn cells into more round/crescent (crescent/round) shapes
and to shift the crescent cell across the midnight MLT meridian. However,
these combinations are associated with lower estimates of the total cross
polar cap potential drop, Φ PC, while the nonreinforcing
combinations produce elevated Φ PC, especially B y −/summer.
There is an overall tendency for Φ PC to increase from winter to
summer, although the pure seasonal effect on the potential drop is weaker
than that of the B y −sign/season factor. We did not find pronounced
differences among the patterns derived for the 5 individual years, which
spanned the most recent interval of solar cycle maximum. Sorting by radar,
we found few differences among the patterns for B y +, but for B y −,
variations emerged that are consistent with a possible dependence on
universal time (UT). The impacts of season and UT on
convection in the high-latitude ionosphere thus depends on the IMF,
especially the sign of B y. We speculate that variability in the ionospheric conductivity has a greater effect on
magnetosphere-ionosphere coupling under B y − conditions.
Copyright
2005 by the American Geophysical Union.
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Comparison
of geosynchronous energetic particle flux responses to solar wind dynamic
pressure enhancements and substorms
Lee D.-Y., L.
R. Lyons, G. D. Reeves (2005), Comparison of geosynchronous energetic particle
flux responses to solar wind dynamic pressure enhancements and substorms, J. Geophys. Res.,
110, A09213, doi:10.1029/2005JA011091.
2005-09-09
Abstract: Geosynchronous energetic particle fluxes are used to
examine the differences and similarities between the particle disturbances
due to an enhancement in solar wind dynamic pressure P dyn
and those caused by substorms. Disturbances are
also distinguished by IMF conditions. First, for not strongly southward IMF
conditions (weakly southward or northward IMF), we find that the magnetospheric compression by a P dyn
enhancement usually causes particle fluxes to increase simultaneously at
all energy channels. The increase is global around the Earth, but it
usually occurs first on the dayside and then propagates to the nightside within a few minutes. We also find that a magnetospheric compression sometimes leads to a flux
decrease or no flux change for at least one energy channel at some MLTs, which we attribute to the shape of radial
profiles at constant adiabatic invariants. However, we find no evidence for
substorm-like injections in our P dyn enhancement events when the IMF is not strongly
southward. Following prolonged strongly southward IMF, substorms
caused by IMF changes that lead to convection electric field reduction and
are not associated with a P dyn change generate
flux disturbances that are quite similar to typical substorm
flux disturbances for less strongly southward IMF conditions. However, the dispersionless injection front is found over a much wider
azimuthal region, sometimes extending to the late
afternoonside for protons. We find that under
prolonged steady, strongly southward IMF conditions, a P dyn enhancement leads to a two-mode type disturbance.
The disturbance due to magnetospheric compression
can be clearly identified and is seen primarily on the dayside, and a substorm-like injection associated with current wedge
formation is seen on the nightside. The dayside
compression effect is seen in both species, but is often more easily
identified in the proton fluxes than in the electron fluxes. The substorm-like injection feature is also seen in both
species but is usually more evident in the electron fluxes. In the events
studied here, the dayside compression disturbance precedes the substorm-like injection on the nightside
by a few minutes.
Copyright
2005 by the American Geophysical Union.
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Solar
wind control of the radial distance of the magnetic reconnection site in
the magnetotail
Nagai T., M.
Fujimoto, R. Nakamura, W. Baumjohann, A. Ieda, I. Shinohara, S. Machida, Y. Saito, T. Mukai (2005), Solar wind control of the radial distance
of the magnetic reconnection site in the magnetotail,
J. Geophys. Res., 110, A09208, doi:10.1029/2005JA011207.
2005-09-09
Abstract: To understand magnetotail
dynamics, it is essential to determine where magnetic reconnection takes
place in the near-Earth magnetotail during substorms. The Geotail
spacecraft thoroughly surveyed the near-Earth plasma sheet at radial
distances of 10–31 R E during the years 1995–2003.
Thirty-four clear reconnection events were identified using the criterion
of strong electron acceleration. Various solar wind parameters prior to
each reconnection event were examined in order to find the factor
controlling the location of the magnetic reconnection site in the magnetotail. The same analyses were carried out for
fast tailward flow events. The most important
factor was determined to be the solar wind energy input, which can be
expressed by − V x × B s, where V x is the x component of the solar
wind velocity and B s is the southward component of the interplanetary
magnetic field. It is likely that higher efficiency of energy input, rather
than the total amount of energy input, primarily controls the location of
magnetic reconnection; magnetic reconnection takes place closer to the
Earth when efficiency of energy input is higher. The effect of solar wind
dynamic pressure is minor. The present result suggests that the tail
magnetic reconnection location during substorms
is controlled by solar cycle variations in the solar wind.
Copyright
2005 by the American Geophysical Union.
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Extreme
solar-terrestrial events of October 2003: High-latitude and Cluster
observations of the large geomagnetic disturbances on 30 October
Rosenqvist L., H. Opgenoorth,
S. Buchert, I. McCrea, O. Amm,
C. Lathuillere (2005), Extreme solar-terrestrial
events of October 2003: High-latitude and Cluster observations of the large
geomagnetic disturbances on 30 October, J. Geophys.
Res., 110, A09S23, doi:10.1029/2004JA010927.
2005-09-17
Abstract: The extremely large solar eruption on 28 October 2003
caused an intense geomagnetic storm at Earth. A second solar eruption on 29
October resulted in a reintensification of the
storm about a day later. Similarities and differences between these two
events in terms of solar eruption, solar wind driver, and their resulting
effect on the near-Earth environment are investigated and put into context
of previous works on storm geoeffectivness.
Within the second storm some of the strongest substorms
in the history of magnetic recordings occurred in northern Scandinavia. The aim of this study is to investigate
the cause and resulting effects of these extreme geomagnetic disturbances
on the ionosphere and upper atmosphere, focusing on the northern
Scandinavian sector where these disturbances reached extremely high values.
During this time period, well after the initial arrival of the
Interplanetary Coronal Mass Ejection (ICME), the Cluster spacecraft were
located at the flank of the magnetospheric tail.
The satellites were passed several times by an inward and consecutively
outward moving magnetopause in close relation to the substorm
intensifications in northern Scandinavia.
We propose that the evolution of these magnetospheric
substorm intensifications are influenced by the
changing dynamics of the solar wind in the form of increased pressure
occurring after a prolonged period of southward Interplanetary Magnetic
Field (IMF) and thus excessive energy loading into the magnetosphere prior
to the onset of the intensifications. We present evidence of external
pressure pulse triggering and possibly also quenching of these substorm onsets and recoveries. In addition, EISCAT
data have been used to investigate the detailed local behavior of the ionospheric plasma, giving rise to such extreme
disturbances. We found that in this case, extreme combinations of enhanced
conductivity and intense electric field resulted in very high current
intensities (westward electrojet ∼7.4 MA) and very fast onset of such currents. The $\frac{{\rm d}B}{{\rm d}t}$ associated
geomagnetically induced currents caused power
failures in southern Sweden.
Copyright
2005 by the American Geophysical Union.
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Flare-generated
shock evolution and geomagnetic storms during the “Halloween 2003 epoch”:
29 October to 2 November
Wu C.-C., et
al. (2005), Flare-generated shock evolution and geomagnetic storms during
the “Halloween 2003 epoch”: 29 October to 2 November, J. Geophys. Res., 110, A09S17, doi:10.1029/2005JA011011.
2005-09-17
Abstract: The October/November 2003 (“Halloween 2003”) epoch of
intense solar flares provided an opportunity to test the results of earlier
parametric 1.5 MHD studies of interacting interplanetary shock waves. These
preliminary studies used an adaptive numerical grid that made it possible
to identify products of these interactions. During 28 October to 2 November
2003, three shocks generated by four solar flares were observed at the L1
libration point by ACE/SWEPAM/SWICS/MAG. Two very distinct geomagnetic
storms, associated with two of these flares (X17/4B and X10/2B), rank as
two of the largest storms of solar cycle 23. The purpose of this paper is
to present the use of an adaptive grid 1.5-dimensional MHD model that is
initiated at the solar surface to study in detail the three shocks observed
at L1 that were generated by the four solar flares. Accordingly, four
separate pressure pulses, at the appropriate times and with different
strengths and duration, determined via a trial and error procedure, are
introduced on the Sun to mimic the four flares. The results show that the
simulated solar wind velocity temporal profiles successfully matched the
observations at L1. The major objective, to demonstrate the detailed nature
of interacting shocks and some of their products after origination from
closely spaced solar events, is achieved. In addition, the MHD model is
able to suggest the solar sources that are associated with specific
geomagnetic storms at Earth.
Copyright
2005 by the American Geophysical Union.
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Decay
of interplanetary coronal mass ejections and Forbush
decrease recovery times
Penna R. F., A. C. Quillens (2005),
Decay of interplanetary coronal mass ejections and Forbush
decrease recovery times, J. Geophys. Res., 110,
A09S05, doi:10.1029/2004JA010912.
2005-09-20
Abstract: We investigate the relation between Forbush
cosmic ray decrease recovery time and coronal mass ejection transit time
between the Sun and Earth. We identify 17 Forbush
decreases from ground-based neutron count rates between 1978 and 2003 that
occur during the same phase in the solar cycle and can be associated with
single coronal mass ejections (CMEs) in the SOHO
LASCO CME Catalog or previously published reports and with specific
interplanetary coronal mass ejections (ICMEs)
crossing the vicinity of Earth. We find an anticorrelation
between Forbush recovery times and CME transit
time that contradicts the predictions of simple cosmic ray diffusive
barrier models. The anticorrelation suggests that
the decay rate of ICMEs is anticorrelated
with their travel speed. Forbush recovery times
range from seven times the transit time for the fastest disturbance to a
fifth the Sun-Earth transit time for the slowest. To account for the large
range of measured recovery times, we infer that the slowest disturbances
must decay rapidly with radius, whereas the fastest ones must remain
strong. The longest recovery times suggest that the fastest disturbances in
our sample decayed less rapidly with radius than the ambient solar wind
magnetic field strength.
Copyright
2005 by the American Geophysical Union.
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Magnetospheric
model of subauroral polarization stream
Goldstein J.,
J. L. Burch, B. R. Sandel (2005), Magnetospheric
model of subauroral polarization stream, J. Geophys. Res., 110, A09222, doi:10.1029/2005JA011135.
2005-09-22
Abstract: We present a magnetospheric
model of the subauroral polarization stream
(SAPS) electric potential, parameterized by Kp
index (valid for Kp = 4–7), on the basis of a
previous study of the average characteristics of SAPS. The model treats the
SAPS westward flow channel as a potential drop whose radial location and
width decrease as a function of both increasing magnetic local time (MLT) and
increasing Kp. The magnitude of the SAPS
potential drop decreases eastward across the nightside
and increases with increasing Kp. The model SAPS
flow channel significantly alters the flow paths of plasma in the afternoon
and evening MLT sectors and agrees with an earlier single-event study that
used an ad hoc SAPS potential to obtain good agreement with plasmasphere observations. The model performance is
tested via comparison with 13 intervals of plasmapause
data obtained during the period 1 April through 31 May 2001 by the extreme
ultraviolet (EUV) imager on the Imager for Magnetopause-to-Aurora Global
Exploration (IMAGE) satellite. Although the model performs well, the
current Kp -based parameterization is somewhat
crude, capturing only the gross spatial and temporal SAPS
characteristics.
Copyright
2005 by the American Geophysical Union.
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On
the origin and configuration of the 20 March 2003 interplanetary shock and
magnetic cloud at 1 AU
Berdichevsky D. B., I. G. Richardson, R. P. Lepping, S. F. Martin (2005), On the origin and
configuration of the 20 March 2003 interplanetary shock and magnetic cloud
at 1 AU, J. Geophys. Res., 110, A09105, doi:10.1029/2004JA010662.
2005-09-23
Abstract: On 20 March 2003, a forward shock was observed in the
near-Earth solar wind, followed 8 hours later by an interplanetary magnetic
cloud (IMC), in a configuration having several uncommon features: Both were
parts of a 38-hour interval containing transient solar outflows that
occurred in an extended high-speed stream from a Y-shaped extension of the
south polar coronal hole. (In contrast, IMCs, and
ejecta in general, were rarely observed within
high-speed streams at low heliolatitudes during
cycle 23.) The most likely solar source for the IMC is AR 10314, located at
S15°, just above the “fork” of the Y-shaped coronal hole. Several solar
flares occurred in this active region on 17–18 March, as well as a
succession of four coronal mass ejections (CMEs).
Velocity considerations narrow the most likely source of the 38-hour
interval of activity to two CMEs on 17 March 2003
associated with solar flares at W33° and W39°. The IMC axis had a
north-south orientation, which is unusual for IMCs
during this solar cycle. Its left-handedness implies an association with a
left-skewed coronal arcade, which is less common in the Southern
Hemisphere. Considering the shock observed ahead of the IMC, we conclude
based on orientation and ram pressure arguments that this shock was not
driven by the IMC, as might be presumed, but was the flank of an unrelated
shock that overtook the IMC approximately halfway between Sun and Earth,
heating the plasma and accelerating particles within the IMC. The CME
associated with the X-class flare, at 1208 UT on 18 March in AR 10314
appears to be the solar source for this shock.
Copyright
2005 by the American Geophysical Union.
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E
× B drift simulation in an Eulerian ionospheric model using the total variation diminishing
numerical scheme
Kulchitsky A., S. Maurits,
B. Watkins, J. McAllister (2005), E × B drift simulation in an Eulerian ionospheric model
using the total variation diminishing numerical scheme, J. Geophys. Res., 110, A09310, doi:10.1029/2005JA011033.
2005-09-23
Abstract: The University of Alaska Fairbanks Eulerian
Polar Parallel Ionospheric Model is a
high-resolution model of the polar ionosphere that incorporates multiple
ion species. This paper briefly describes this model and the implementation
of the total variation diminishing (TVD) advection scheme. The model is
based on an Eulerian framework. It is
demonstrated that the minimal numerical diffusion of the TVD advection
scheme is critical for maintaining ion density gradients with
high-resolution Eulerian ionospheric
models. The performance of this method is discussed and compared with an
upwind numerical scheme. A sample model run for 24 October 2003 that
simulates the formation of polar cap ionospheric
structures is presented. The results using the TVD advection scheme are
compared with the corner transport upwind advection scheme to demonstrate
the advantage of the TVD method for simulating steep density gradients and
small-scale density structures. These small-scale density features result
from time-varying electric fields and are commonly observed using experimental
techniques (e.g., incoherent scatter radar) in polar regions.
Copyright
2005 by the American Geophysical Union.
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Energetic
particle observations from the Ulysses COSPIN instruments obtained during
the October–November 2003 events
McKibben R. B., J. D. Anglin, J. J.
Connell, S. Dalla, B. Heber, H. Kunow, C. Lopate, R. G. Marsden, T. R. Sanderson, M. Zhang (2005), Energetic
particle observations from the Ulysses COSPIN instruments obtained during
the October–November 2003 events, J. Geophys.
Res., 110, A09S19, doi:10.1029/2005JA011049.
2005-09-27
Abstract: We report comprehensive observations of solar energetic
particle intensities at energies from 0.3 to >100 MeV
made by the suite of six Ulysses COSPIN energetic charged particle instruments
on the Ulysses spacecraft during the period of intense solar activity in
October/November 2003. We also discuss observations of particle
anisotropies in selected energy ranges made by these instruments. Located
near the orbit of Jupiter and only about 6
Copyright
2005 by the American Geophysical Union.
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Relativistic
nucleon and electron production in the 2003 October 28 solar event
Miroshnichenko L. I., K.-L. Klein, G. Trottet,
P. Lantos, E. V. Vashenyuk, Y. V. Balabin, B. B. Gvozdevsky
(2005), Relativistic nucleon and electron production in the 2003 October 28
solar event, J. Geophys. Res., 110, A09S08, doi:10.1029/2004JA010936.
2005-09-30
Abstract: A flare on 2003 October 28 produced a relativistic
particle event at Earth, although the active region AR 10486 was located to
the east of the central meridian of the Sun. The paper considers features
related to the acceleration at the Sun and the propagation to the Earth of
energetic particles in this event, which occurred on a disturbed
interplanetary background caused by preceding activity on the Sun and a corotating high-speed solar wind stream. From a study
of the onset times of the event at different neutron monitors, we conclude
that the earliest arriving solar particles were neutrons. The first
relativistic protons arrived a few minutes later. Among relativistic solar
protons (RSP), two populations could clearly be distinguished: prompt and
delayed ones. The prompt solar protons caused an impulse-like increase at a
few neutron monitor stations. The delayed solar protons arrived at Earth
0.5 hours later. Both prompt and delayed relativistic protons arrived at
Earth from the antisunward direction. On the
other hand, subrelativistic electrons that were
traced by their radio emission from meter waves (Nançay
Radioheliograph and Decametric
Array) to kilometer waves (Wind/WAVES) are accompanied by metric radio
emission in the western solar hemisphere, far from the flaring active
region. We propose a scenario that reconciles the unusual features of
energetic particles at the Earth with the observed structure of the
interplanetary magnetic field, which suggests the Earth is at the interface
between an interplanetary coronal mass ejection (ICME) and a corotating stream during the event. In this scenario
the high-energy protons and electrons are accelerated in the flaring active
region, injected into the eastern leg of an ICME loop rooted in the active
region, and reach the Earth from the antisunward
direction after passing through the summit of the loop. We attribute the
promptly escaping subrelativistic electrons to
acceleration in the western solar hemisphere and propagation along the
nominal Parker spiral.
Copyright
2005 by the American Geophysical Union.
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From
the Sun to the outer heliosphere: Modeling and
analyses of the interplanetary propagation of the October/November
(Halloween) 2003 solar events
Intriligator D. S., W. Sun, M. Dryer, C. D. Fry, C. Deehr, J. Intriligator
(2005), From the Sun to the outer heliosphere:
Modeling and analyses of the interplanetary propagation of the
October/November (Halloween) 2003 solar events, J. Geophys.
Res., 110, A09S10, doi:10.1029/2004JA010939.
2005-09-30
Abstract: We use the space weather validated 3-D HAFv2 model to help
us study the interplanetary propagation of the October/November 2003 solar
eruptions from the Sun to >90 AU and over a wide range of heliolongitudes and heliolatitudes.
The HAFv2 model predictions at ACE (1 AU), Ulysses (5.23 AU), Cassini (8.67
AU), Voyager 2 (73 AU), and Voyager 1 (93 AU) are compared with available
data. These comparisons indicate the importance of asymmetric
interplanetary propagation both in heliolongitude
and heliolatitude. We recommend that these
effects explicitly be taken into account. The HAFv2 results appear to be
useful for interpreting the Voyager 2 and Voyager 1 energetic particle data
in the outer heliosphere. They are consistent
with the effects of the Halloween solar events observed in the energetic
particle data at both spacecraft. The HAFv2 results also may be helpful for
predicting the plasma wave 2–3 kHz radio emission previously associated
with large shocks and their interaction with the heliopause.
Our study indicates that the Halloween events may give rise to 2–3 kHz
radio emission in early 2005, assuming that the shocks which propagated
beyond Voyager 1 will be strong enough.
Copyright
2005 by the American Geophysical Union.
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Effect
of solar wind pressure enhancements on storm time ring current asymmetry
Shi Y., E. Zesta, L. R. Lyons, A. Boudouridis,
K. Yumoto, K. Kitamura (2005), Effect of solar
wind pressure enhancements on storm time ring current asymmetry, J. Geophys. Res., 110, A10205, doi:10.1029/2005JA011019.
2005-10-08
Abstract: The effect of solar wind pressure enhancements on storm
time ring current asymmetry is investigated by examining the asymmetric
variations in the north-south (H) and east-west (D) components of the
geomagnetic field during four magnetic storms. For two strong storms, on 25
September 1998 and 29 May 2003, pressure enhancements occurred during the
main phase with strong and steadily southward IMF B z. It is found that the
pressure enhancements significantly increase the asymmetry of the already
strong and asymmetric ring current under these conditions. For the moderate
magnetic storm on 10 January 1997, a pressure enhancement occurred during
the early recovery phase when IMF B z was turning northward while it was
still southward. Our result shows that the pressure enhancement also
slightly enhanced the asymmetry of the slightly asymmetric ring current
that existed during the early recovery phase. On 6 November 2000, a
pressure enhancement occurred during the late recovery phase when the IMF B
z was strongly northward. For this case, the pressure enhancement did not
increase the asymmetry of the already symmetric ring current. The above
results of ring current asymmetry increases can be explained by considering
the local energization of the preexisting ring
current particles by the azimuthal electric field
induced by the pressure enhancement. Our results show that the effect of
pressure enhancements on the ring current depends strongly on the asymmetry
state of the ring current at the times of the onsets of pressure
enhancements, which is in turn determined by the IMF B z preconditioning.
In addition, the size and relative strength of a pressure enhancement also
play important roles in affecting the ground asymmetric H
perturbation.
Copyright
2005 by the American Geophysical Union.
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Electron
signatures of active merging sites on the magnetopause
Maynard N. C.,
W. J. Burke, J. D. Scudder, D. M. Ober, D. R.
Weimer, K. D. Siebert, C. T. Russell, M. Lester, F. S. Mozer,
N. Sato (2005), Electron signatures of active merging sites on the
magnetopause, J. Geophys. Res., 110, A10207, doi:10.1029/2004JA010639.
2005-10-13
Abstract: Near magnetopause current layers the Polar satellite often
detects field-aligned fluxes of >0.5 keV
electrons that carry heat flux away from merging sites along inner/outer separatrices between newly opened and
closed/interplanetary magnetic flux. Close to separator lines, electron gyrotropy weakens to break trapping on closed field
lines of the outer plasma sheet followed by attachment to newly opened flux
at random pitch angles. Energetic electrons in the “tails” of distribution
functions quickly move great distances along separatrices
to act as surgical indicators of active merging. If IMF B Y is large, field
rotation in the magnetopause current layer can be $\ll$
180
Copyright
2005 by the American Geophysical Union.
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Characteristics
of the interplanetary coronal mass ejections in the heliosphere
between 0.3 and 5.4 AU
Wang C., D. Du,
J. D. Richardson (2005), Characteristics of the interplanetary coronal mass
ejections in the heliosphere between 0.3 and 5.4
AU, J. Geophys. Res., 110, A10107, doi:10.1029/2005JA011198.
2005-10-14
Abstract: We identify and characterize interplanetary coronal mass
ejections (ICMEs) observed by spacecraft in the
solar wind, namely Helios 1 and 2, PVO, ACE, and Ulysses, which together
cover heliocentric distances from 0.3 to 5.4 AU. The primary identification
signature used to look for ICMEs is abnormally
low proton temperatures. About 600 probable ICMEs
were identified from the solar wind plasma and magnetic field data from
these spacecraft. We use these events to study the radial evolution of ICMEs between 0.3 and 5.4 AU, mainly in a statistical
sense. The occurrence rate of ICME approximately follows the solar activity
cycle. ICMEs expand as they move outward since
the internal pressure is generally larger than the external pressure. The
average radial width of ICMEs increases with
distance. ICMEs expand by a factor of 2.7 in
radial width between 1 and 5 AU. The radial expansion speed of ICMEs decreases with distance and is of the order of
the Alfvén speed. The density and magnetic field
magnitude decrease faster in ICMEs, which fall
off with distance R as R −2.4 and R −1.5, respectively, than in
the ambient solar wind; however, the temperature decreases as R −0.7,
slightly less rapid than in the ambient solar wind. These results are
consistent with previous findings with relatively limited data coverage. We
also use a one-dimensional MHD model to investigate the radial expansion of
the ICMEs and find that the radial expansion
speed is of the order of the Alfvén speed,
consistent with the observations.
Copyright
2005 by the American Geophysical Union.
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