ACE Browse Parameter Information





GENERAL INFO     CRIS     EPAM     MAG     SEPICA     SIS     SWEPAM     SWICS     ULEIS



General Information

Browse parameters are a subset of measurements by the ACE instruments which are created at the Science Center during level one processing. They are delivered to the public domain as soon as possible. Their purpose is to allow monitoring of the solar wind and large-scale particle and magnetic field behavior, and selection of interesting time periods for more intensive study. Interesting time periods might include solar energetic particle events, or the passage of an interplanetary shock. An additional use of the browse parameters is to investigate relationships between the data from the various ACE instruments, and between ACE data and data from other sources.

If you are looking for data suitable for scientific studies, you need ACE Level 2 data.

The browse parameters include unsectored fluxes of ions at many different energies and electrons at a few energies. They also include the interplanetary magnetic field, and solar wind parameters such as proton speed and temperature. They therefore furnish a very abbreviated description of what is being observed by the ACE instruments, without the relatively high cost of storing and analyzing all the level one data. Eventually they may be supplemented with event data from the particle detectors, but experience with the flight data is a prerequisite for delivering useful products of that type.

Because the browse parameters are intended to be delivered to the public domain within a few days of receipt of the raw data from the spacecraft, they are not subjected to any prior scrutiny by the science teams. Their production is automatic, and the data are not routinely checked for accuracy before release. Therefore the browse parameters are not suitable for serious scientific work, and should not be cited without first consulting the appropriate ACE instrument team. However, the algorithms used to create the browse parameters are subject to revision, and their reliability is expected to improve with time. The browse parameters will probably be the most popular Science Center product for the larger community outside the instrument teams, particularly during the early stages of the mission, so early delivery is considered more important than full verification.

The best time resolution for the browse parameters is generally limited by data collection cycles in the instruments. CRIS and SIS have separate 256-second cycles and SWICS has a 12-minute cycle. EPAM, ULEIS and SEPICA have separate 128-second cycles, each cycle containing data for 10 consecutive spacecraft spins. SWEPAM has a 64-second cycle and MAG browse data is reported with 16-second time resolution. The SWIMS instrument does not contribute to the browse parameters.

In addition to the cycle/averaging periods noted above, all the browse parameters are averaged to common one-hour and one-day periods, and the data from EPAM, MAG, SEPICA, SWEPAM and ULEIS are also averaged to a common 5-minute period. These common periods are in time phase with UTC clock, i.e., at integral 5-minute, hour and day values.

The charged particle fluxes in the browse data include H, He, C, O, Mg+Si, Ne--Fe, and iron-group fluxes, in various energy bands. This list may be augmented in the future, and the energy bands may be revised by the instrument teams as the data analysis proceeds.

The solar wind parameters include the proton speed, proton density, radial component of the proton temperature tensor, and the He++/proton ratio, all from SWEPAM, and the following parameters from SWICS: He speed, He and oxygen thermal speed, coronal temperature, and the He/O and Fe/O density ratios. The interplanetary magnetic field vector and magnitude from MAG are reported in both RTN and GSE coordinate systems. It should be noted that the attitude, position and velocity of the ACE spacecraft are also made available to the public by the Science Center, in various coordinate systems.

To see a summary of the browse data items we provide (or plan to provide), have a look at the ACE Browse Parameter List. top




CRIS



CRIS measurements of the flux of cosmic ray nuclei with nuclear charge Z>=10 and kinetic energy from ~100 to ~400 MeV/nuc are derived from the counting rate of Ne to Ni nuclei (nuclear charge 10<=Z<=28) that stop in the four CRIS "telescopes", each composed of fifteen 3-mm thick solid state detectors. These particles have energies at the approximate maximum of the galactic cosmic ray energy spectrum (as measured at 1 AU) and they are expected to vary relatively slowly over the 11-year solar cycle, in approximate anti-correlation with the sunspot number. The maximum expected flux is somewhat less than 10-6 per cm2ster.sec at solar minimum, dropping down to a minimum value that is expected to be only 10% to 20% of this during solar maximum conditions. These long-term variations, commonly referred to as the "solar modulation" of cosmic rays; reflect processes by which the solar wind and interplanetary magnetic field tend to prevent cosmic rays from the Galaxy from penetrating into the inner solar system. For additional information, contact Richard Mewaldt (mewaldt@srl.caltech.edu) or Rick Leske (ral@srl.caltech.edu).

Qualifying Remarks:
The labeled energy range (~100 to 400 MeV/nucleon) is not actually the same for all of the included elements; rather, these are characteristic values. The actual energy range varies from ~80 to 300 MeV/nuc for Ne to ~200 to ~550 MeV/nuc for Fe. Note that Ne, Mg, Si, and Fe (Z = 10, 12, 14, and 26) dominate the abundance of cosmic rays with Z>=10; the reported flux values assume for simplicity that all events are Si. As a result, the absolute value of the reported flux is not straightforward to interpret, but time variations in this flux should be representative of heavy cosmic ray nuclei in the indicated energy range.
        Although large solar energetic particle events occasionally accelerate heavy nuclei to energies >100 MeV/nuc, the CRIS instrument is not designed to return accurate flux measurements under these conditions, and so the reported flux levels at these times may not be reliable. During such periods of intense particle fluxes the user is encouraged to refer to data from other ACE instruments, including SEPICA, ULEIS, and SIS.

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CRIS measurements of the flux of cosmic ray nuclei with nuclear charge Z>=10 and kinetic energy greater than ~300 MeV/nuc are derived from the counting rate of those particles that penetrate the entire CRIS instrument, in either direction, if they lose sufficient energy in one of the 4.5-cm thick silicon detector stacks. At these high energies the flux of cosmic ray nuclei is expected to vary only slowly over the 11-year solar cycle, from a maximum value of somewhat less than 10-3 per cm2ster.sec at solar minimum, to a minimum value that is expected to be somewhat less than 1/2 of this during solar maximum conditions. These long-term variations are commonly referred to as the "solar modulation" of cosmic rays; they reflect processes by which the solar wind and interplanetary magnetic field tend to prevent cosmic rays from the Galaxy from penetrating into the inner solar system. For additional information, contact Richard Mewaldt (mewaldt@srl.caltech.edu) or Rick Leske (ral@srl.caltech.edu).

Qualifying Remarks:
Neither the labeled energy range (>=300 MeV/nucleon) or the element range (Z>=10) are exact; these are characteristic values. The actual energy range varies from >300 MeV/nuc for Ne (Z=10) to 2500 MeV/nuc for Fe (Z=26), but note that most cosmic rays have energies of several GeV/nucleon and greater, so these differences are not critical. The reported flux values are also expected to contain some contribution from tighter cosmic rays (6 <= Z <= 8) with energies from ~200 to ~500 MeV/nuc, but these cosmic rays should show a similar time behavior.

This browse parameter is derived from particles that enter from either end of the CRIS telescope and then pass entirely through. No corrections have been applied to account for the fact that cosmic rays coming from the rear must pass through considerable spacecraft material. In addition, the CRIS instrument is not designed to return accurate flux measurements during large solar particle events. As a result of these uncertainties the reported flux values should be treated as a qualitative, rather than a quantitative, measure of cosmic ray modulation.

For more information on CRIS, see The CRIS/SIS Home Page.

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EPAM


Brief description of EPAM browse parameters.
The Electron, Proton, and Alpha Monitor (EPAM) is designed to make measurements of ions and electrons over a broad range of energy and intensity. Through five separate solid-state detector telescopes oriented so as to provide nearly full coverage of the unit-sphere, EPAM can uniquely distinguish ions (E > 47 keV) and electrons (E > 38 keV) providing the context for the measurements of the high sensitivity instruments on ACE.

The browse parameters contain spin averaged data coming from two of the five EPAM telescopes. EPAM is also part of the real-time Solar Wind (RTSW) system developed by NASA and NOAA. The instrument provides 24 hour coverage of the space weather environment as measured by ACE. For additional information contact Dennis Haggerty (Dennis.Haggerty@jhuapl.edu) or Rob Gold (Robert.Gold@jhuapl.edu) .

Note: The lowest energy (P1) 47-65 keV Ion data are suspect from late November 2001, through October 2003. After October 2003, the P1, P3, P5 and P7 Ion channels are derived from a different EPAM telescope (see below).




Descriptive text for this browse parameter

This 761-1220 keV ion channel is on a telescope referred to as LEFS60 (Low Energy Foil Spectrometer). An aluminized Parylene foil is used to absorb ions with energies below 350 keV while allowing ions above 350 keV to pass through to the solid-state detector. The telescope is mounted at 60 degrees to the spacecraft spin axis. The geometrical factor for this channel is 0.397 (cm2.sr).

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Descriptive text for these browse parameters

These channels come from EPAM's Low-Energy Magnetic Spectrometer which is oriented at 30 degrees from the spacecraft spin axis and is known as the LEMS30 telescope. The LEMS30 telescope contains a rare-earth magnet in front of the detector and sweeps out electrons with energy below about 500 keV. The flux conversions for these browse channels use a geometrical factor of 0.428 (cm2 sr).

After October 2003, these ion data are derived from the LEMS120 telescope, oriented at 120 degrees from the spacecraft spin axis. This change is due to noise problems with the ion channels in the LEMS30 telescope.

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Descriptive text for these browse parameters

These deflected electron channels are a byproduct of EPAM's Low-Energy Magnetic Spectrometer which is oriented at 30 degrees from the spacecraft spin axis and is known as LEMS30. The rare-earth magnet in front of the LEMS30 detector deflects electrons away from the ion detector and samples them in a separate detector known as the B detector. Only deflected electrons can reach the B detector so it is not susceptible to ion contamination The geometrical factor for these channels is 0.14 (cm2 sr).


EPAM Home Page.

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MAG


MAG Browse Description



The Magnetic Field Experiment (MAG) consists of twin vector fluxgate magnetometers controlled by a common CPU. The sensors are mounted on booms extending 4.19 meters from the center of the spacecraft at opposite sides along the +/-Y axes of the spacecraft. The instrument returns 6 vector measurements each second, divided between the two sensors, with onboard snapshot and FFT buffers to enhance the high-frequency resolution.

Browse data for the MAG instrument consists of 16-second, major-frame averages of the measured magnetic field with subsequent analysis yielding 5-minute, 1-hour and 1-day averages consistent with Browse data from other ACE instruments. Instrument offsets, including spacecraft fields, are derived from past weeks of data and necessarily lag behind the most accurate values computed for use in Level-2 analyses. Users of Browse data should be aware that spurious AC signals, such as possible spacecraft or instrument noise, are not detected and are not removed from the Browse analysis. Depending on the accuracy and stability of offsets applied in the above manner, spacecraft spin tones may be evident in the data. MAG data is not guaranteed during spacecraft maneuvers and spacecraft nutation is likely to contribute directional errors following maneuvers.

Description of MAG browse parameters:

MAG Browse data is not validated by the experimenters and should not be used except for preliminary examination prior to detailed studies.

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SEPICA


Brief Description of the SEPICA Browse Parameters

The Solar Energetic Particle Charge Analyzer (SEPICA) determines the nuclear charge (Z), or element number, energy (E) and ionic charge state (Q) of incoming energetic ions. Z and E are determined by a combination of a thin-window proportional counter and a silicon detector as a ÆE versus E telescope for energies from 0.3 MeV/nuc to 6 MeV/nuc (He) or 18 MeV/nuc (O). A multislit-collimator electrostatic analyzer combination with position measurement in the multi-wire proportional counter allows the determination of the ionic charge state for energies up to ~ 5 MeV/Q. With these characteristics the SEPICA instrument is mainly sensitive to energetic ion populations from solar flares. It also records ion flux enhancements in interplanetary space that originate from acceleration at interplanetary traveling shocks, for example ahead of coronal mass ejections (CMEs), and in co-rotating interaction regions where solar wind streams with different speeds meet. More information on the instrument may be found on the WWW site of the SEPICA team at the University of New Hampshire.

The SEPICA Browse Parameter set contains selected elemental fluxes for H, He, C, O and Fe integrated over the main energies ranges that SEPICA is sensitive to.

  Cautionary Notes:



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SIS


Brief Description of the SIS Browse Parameters




Note: During periods of high solar activity, the livetime for this browse parameter may not be calculated correctly, resulting in incorrect flux values.
Two noisy matrix strip in the instrument were turned off on 2000-318. These strips were causing the livetime for this browse parameter to be calculated incorrectly. This is the cause of the apparent large drop in flux on 2000-318.

Integral flux of high-energy solar protons from the T4 and T67 counting rates of the Solar Isotope Spectrometer (SIS). These browse parameters are designed to emulate the SIS proton rates contained in ACE Real Time Solar Wind Data from NOAA.

During solar quiet times, these fluxes are contaminated by background from particles entering from the sides of the instrument.

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Note: During periods of high solar activity, the livetime for this browse parameter may not be calculated correctly, resulting in incorrect flux values.
Two noisy matrix strip in the instrument were turned off on 2000-318. These strips were causing the livetime for this browse parameter to be calculated incorrectly. This is the cause of the apparent large drop in flux on 2000-318.

This browse parameter is derived from the counting rate of energetic CNO nuclei that stop in the two solid state detector telescopes that make up the Solar Isotope Spectrometer (SIS). Included are events with nuclear charge 3 <= Z <= 9 that trigger detectors M1 and M2, and then stop before triggering detector D1. The 3 <= Z <= 9 element range is always dominated by C, N, and O nuclei, independent of the source of the particles being observed.

During solar minimum (e.g., 1992 to 1998), on days when the Sun is quiet, the 7 to 10 MeV/nuc energy interval is dominated by anomalous cosmic ray (ACR) nitrogen and oxygen, with a small contribution (<10%) from galactic cosmic rays (GCRs). Anomalous cosmic rays originate from interstellar neutral particles that are swept into the heliosphere, ionized, picked up by the solar wind and carried to the solar wind termination shock, where they are accelerated to energies of ~1 to ~50 MeV/nuc. The flux of these nuclei sometimes varies by as much as a factor of ~2 over the 27 day solar rotation period in response to interplanetary conditions. The ~40 cm2sr geometry factor of SIS allows these variations to be seen clearly. As we move toward solar maximum conditions in 1999 and beyond, the flux of ACRs is expected to decrease by a factor of ~100 or more, as it becomes more difficult for low energy cosmic rays to enter the inner heliosphere.

During large solar energetic particle (SEP) events, the intensity of low energy nuclei in interplanetary space can increase by factor of 10 to 1000 or more, and for days at a time, this energy interval can be dominated by solar energetic particles with C:N:O ~ 0.4:0.15:1. An example of such an event is seen in early November of 1997 (~Day 310). The quiet time intensity measured by this browse parameter should vary from ~10-8 per cm2sr.sec.MeV/nuc at solar maximum to ~10-6 per cm2sr.sec.MeV/nuc at solar minimum. During large solar particles events it could be as high as ~1 per cm2sr.sec.MeV/nuc.

Qualifying Remarks:

Note that the energy intervals for the most abundant elements C, N, and O all differ somewhat from the nominal values of 7 to 10 MeV/nuc.

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Note: During periods of high solar activity, the livetime for this browse parameter may not be calculated correctly, resulting in incorrect flux values.
Two noisy matrix strip in the instrument were turned off on 2000-318. These strips were causing the livetime for this browse parameter to be calculated incorrectly. This is the cause of the apparent large drop in flux on 2000-318.

This browse parameter is derived from the counting rate of energetic CNO nuclei that stop in the two solid state detector telescopes that make up the Solar Isotope Spectrometer (SIS). Included are events with nuclear charge 3 <= Z <= 9 that trigger detectors M1 and M2 then stop in either D1 or D2. This element range 3 <= Z <= 9 is always dominated by C, N, and O nuclei, independent of the source of the particles being observed.

This browse parameter responds mainly to anomalous cosmic rays during solar-minimum quiet times, to galactic cosmic rays during solar maximum quiet times, and to solar particles during large solar energetic particle events (see discussion for the 7 to 10 MeV/nuc CNO browse parameter). The quiet time flux should vary from a few x 10-8 per cm2sr.sec.MeV/nuc at solar maximum to ~10-5 per cm2sr.sec.MeV/nuc at solar minimum. During large solar particles events it could be as high as ~0.1 per cm2sr.sec.MeV/nuc.

Qualifying Remarks:

Note that the energy intervals for the dominant elements C, N, and O all differ somewhat from the nominal values of 10 to 15 MeV/nuc, and that the relative abundance of the contributing elements depend on the source of the particles, as noted above and in the description of other SIS browse parameters.

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Note: During periods of high solar activity, the livetime for this browse parameter may not be calculated correctly, resulting in incorrect flux values.
Two noisy matrix strip in the instrument were turned off on 2000-318. These strips were causing the livetime for this browse parameter to be calculated incorrectly. This is the cause of the apparent large drop in flux on 2000-318.

SIS measurements of the intensity of ~9 to ~21 MeV/nuc Z>=10 nuclei are derived from the counting rate of energetic nuclei that stop in the two solid state detector telescopes that make up the Solar Isotope Spectrometer (SIS). Included are events with nuclear charge 10<=Z<=28 (Ne to Ni) that trigger detectors M1 and M2 and then stop in either M2, D1, or D2. The most abundant elements in the element range 10<=Z<=28 are Ne (Z=10), Mg (Z=12), Si (Z=14) and Fe (Z=26).

During solar quiet times this browse parameter responds mainly to galactic cosmic rays, with an admixture of anomalous cosmic ray Ne (see also discussion of 7 to 10 MeV/nuc CNO browse parameter from SIS). During large solar particle events the intensity can be orders of magnitude greater for periods of days. The quiet time intensity should vary from ~10-8 per cm2sr.sec.MeV/nuc at solar maximum to a few times 10-7 per cm2sr.sec.MeV/nuc at solar minimum. During large solar particle events the intensity could rise to >10-2 per cm2sr.sec.MeV/nuc.

Qualifying Remarks:

Note that the quoted energy interval of ~9 to 21 MeV/nuc is strictly valid only for Si. For Ne the corresponding interval is ~8 to ~17 MeV/nuc, while for Fe it is ~12 to ~26 MeV/nuc.

For more information on SIS, see The CRIS/SIS Home Page.

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SWEPAM


Brief Description of the SWEPAM Browse Parameters


Proton density (np) -
is the proton number density in units of cm-3, as calculated by integrating the ion distribution function.

Proton speed (vp) -
is the solar wind proton speed, or more generally just the solar wind (bulk) speed. It is also obtained by integrating the ion (proton) distribution function.

Helium ratio (nHe/np) -
is the ratio of the number density of helium++ ions to the number density of protons.

The radial component of the proton temperature (Tp,rr) -
is the (1,1) component of the temperature tensor, along the radial direction. Again, it is obtained by integration of the ion (proton) distribution function.

For more information contact Dave McComas (dmccomas@swri.edu) or visit the SWEPAM website at http://swepam.lanl.gov.

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SWICS


Brief Description of the SWICS Browse Parameters


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ULEIS


Brief Description of the ULEIS Browse Parameters


The Ultra Low Energy Isotope Spectrometer (ULEIS) determines the mass (M) and energy of incoming energetic ions by measuring their speed and total kinetic energy. Based on the mass identification, the atomic number (Z) is inferred: for example, atomic mass = 1 corresponds to Hydrogen, 3 to the light isotope of He, 4 to 4He, 16 to oxygen, and 56 to Iron. ULEIS responds to ions over the general energy range ~45 keV/nucleon to a few MeV per nucleon, that is, particles with speeds from about 3,000 km/second to 30,000 km/second. Ions of these energies are accelerated from several sources:

The different elements covered by the ULEIS browse parameters give clues to the source of the ions being observed at a given time: for example, events with large 3He abundance, or large Fe/O (0.1 to 1) ratios are solar in origin, while anomalous cosmic rays have little or no 3He and a small Fe/O ratio (about .01). The energy ranges covered also give clues to the particle source: for example, large solar flares produce large increases in ULEIS browse flux boxes from 0.64 to 1.28 MeV/nucleon, while particles escaping from the magnetosphere will show increases only in the lower energy flux boxes (0.08-0.16 MeV/nucleon).

The ULEIS browse parameter fluxes are derived from a computer program operating on the spacecraft in the instrument's data processing unit (DPU). A table of values corresponding to particle speeds and energies is stored in the DPU, and each incoming ion's speed and energy is compared with the table.

Notes on the accuracy of ULEIS browse fluxes:

For more information on how ULEIS works, see the ULEIS Home Page, or contact

Glenn Mason email:(mason@sampx3.umd.edu).
Department of Physics                           tel:  301-405-6203
University of Maryland                          fax:  301-314-9547
College Park, MD  20742

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