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 | |