02-09-2021 Re-release of the SWEPAM Level 2 data for Bartels
rotations 2448 - 2533 (12/29/2012 thru 05/08/2019).
=============================================================
SWEPAM Level 2 data from 2013 to the present have been reprocessed to account
for changes in CEM detector gains over time. While for many years gain
changes were observed in only 2 of the detectors, in recent years additional
detectors have begun to show gain changes. This reprocessing accounts for
changes in these additional detectors with time, and significantly improves
the density values calculated from SWEPAM data.
Spacecraft pointing continues to have a significant effect on SWEPAM moments
quality, but this new data set extends the range of pointing angles at
which valid moments can be calculated.
01-24-2008 Re-release of the SWEPAM Level 2 data for Bartels
rotations 2366 - 2372 (12/07/2006 thru 06/13/2007).
=============================================================
Data have been reprocessed to incorporate updated instrument calibrations
which account for changing CEM gains over time. Changes were based on weekly
on-board calibrations.
04-03-2007 Re-release of the SWEPAM Level 2 data for Bartels
rotations 2342-2361 (02/27/2005 thru 08/20/2006).
=============================================================
Data have been reprocessed to incorporate updated instrument
calibrations. Based on increased time at CEM voltage Level 2, the
instrument geometric factors have been better defined, particularly
for the off-axis CEMs. We also better account for changing CEM gains
over time, based on weekly on-board calibrations.
02-14-2006 Re-release of the SWEPAM Level 2 data for Bartels rotations
2342 - 2348
=============================================================
Incorporates the new geometric factors for operation at CEM voltage level 2.
As we've discussed in the past, invalid speeds are mainly due to times with
penetrating radiation (at which times all moments parameters tend to be bad).
30-minute data are available for most of these periods, from the SWEPAM
instrument team (rskoug@lanl.gov).
Invalid densities and temperatures occur mainly at low speeds, below 320-350 km/s
or so (also depends on the solar wind angle relative to the spacecraft orientation).
Valid data statistics over the entire time period are:
N: 88.4% valid, V: 98.2% valid, T: 88.7% valid
For the last 6 months (Mar - Aug 2005), the values are:
N: 87.9% valid, V: 99.5% valid, T: 92.2% valid
For comparison, in the original version of the Level 2 data for this period,
~65% of the density points were valid.
03-31-2005 Re-release of the SWEPAM Level 2 data for Bartels rotations
2331 - 2335, and rotation 2324
=============================================================
This change was required to update the instrument calibrations. This
is done to account for changing CEM gains, and is based on weekly
on-board calibrations done by sweeping the CEM voltages. Gain
changes have been observed in 2 of the ion CEMs. Starting with
rotation 2331, these changes became large enough that a new algorithm
was required to determine the gain changes with time. The new
calibrations will be incorporated in data from 2004 day 146 through
2005 day 081. Following that time, the CEM detector voltage level
has been increased, taking the instrument back to a non-slipped gain
level. We will of course continue to monitor the instrument
performance to account for future variations with time.
The re-release of rotation 2324 is to remove some additional points
during the 2003 Halloween storms, based on our more recent understanding
of the data quality.
05-28-2003 Release of new version of the SWEPAM Level 2 data
for the entire mission
============================================================
Changes for this release are:
1) Included updated instrument calibrations. This is done to account
for changing CEM gains, and is based on weekly on-board calibrations
done by sweeping the CEM voltages. Gain changes have been observed
in 2 of the ion CEMs, dating back to the beginning of the mission.
The gain changes very slowly with time, so these effects are most
significant later in the mission. The new calibrations will be
incorporated in all future data.
2) Included velocities even at times when all other moments are
unreliable. The speed moment is easiest to calculate, and so it is
often valid even when other moments are not. The philosophy will be
continued in all future data releases.
3) Reprocessed data during most solar particle events to account for
the high background levels. Although the tracking of the solar wind
beam by the instrument can get confused during such times, data are
recoverable from many such intervals, and the required reprocessing
has been done for these times.
12-13-2002 Release of new version of the SWEPAM Level 2 data
for Bartels rotations 2295 and 2297 (09/07/2001 through 10/03/2001
and 10/31/2001 through 11/26/2001)
==================================================================
The SWEPAM team has released a new version of the SWEPAM Level 2 data for
Bartels rotations 2295 and 2297. This change adds some data points during the
high background intervals on days 267-270, 309-310, and 327-328 in 2001 (Sept
24-27, 2001, Nov 5-6, 2001, and Nov 23-24, 2001). All of the data points in
the previous version remain the same, they have just reprocessed and recovered
some additional data for this time period. The SWEPAM team has also produced
a data file filling in the remaining gaps on days 268-269, 310-311, and 328 in
2001. These are not level 2 quality data, but the data are available on
request from the team (Ruth Skoug, rskoug@lanl.gov).
Changes for SWEPAM Team software version 2.01, June 2002:
=============================================================
Data have been reprocessed for Bartels rotations 2279-2295. This
reprocessing was done to account for changing CEM gains by
incorporating the results of the weekly on-board calibrations. No
gain changes were observed prior to mid-2000, and the gain changes
vary slowly with time. Thus changes due to this procedure are
generally small, although they become more significant at later
times. By rotation 2295, typical changes in density (from the
previously released Level 2 values) are ~10%, changes in temperature
are ~5%, and changes in speed are less than 0.5%. Note also that all
future Level 2 data will include these improved calibrations.
Changes for SWEPAM Team software version 2.01, September 2000:
=============================================================
1. Alpha/proton density ratios are now included in the files.
2. The aberation due to the motion of the Earth and the spacecraft is now
included in both the scalar solar wind speed and in the solar wind velocity
components.
3. We have improved our calculation of the instrument geometry factors, and
this release uses our most recent, best values for the geometry factors.
While this change has a small effect on most data points, it is only
significant at low solar wind speeds (<400 km/s), and allows us to extend
the range of valid data down to speeds of approximately 320 km/s.
4. More bad data points have been removed.
5. The fill value for missing data has been changed from -999.9 to -9999.9
============
INTRODUCTION
============
This directory contains Level 2 hand-checked moments for the SWEPAM
instruments on the Advanced Composition Explorer spacecraft.
SWEPAM consists of two independent instruments, one ion and one
electron monitor. Combining their data sets is a PITA, so we have
two separate types of files:
* ion moments files are of the form "swepam-swi-level2-XXXX.hdf",
where "XXXX" is the Bartels cycle number for the collection. The
extension indicates that the files are in NCSA's Hierarchical Data
Format. See for information on
reading HDF files.
The file "swepam_dswi_level2.h" contains a C data structure
suitable for feeding to ASC's wonderful "hdfgen.pl" script.
hdfgen.pl will generate lovely C code to read in these HDF
files and populate values in a usable C struct. See
for details on hdfgen.pl.
* electron moments files are in ASCII format.
====================
Caveats and Warnings
====================
During periods of extremely high solar activity, such as the Bastille
Day event (July 14 2000) the SWEPAM instrument is affected by energetic
particles that penetrate the spacecraft and instrument and make
spurious counts in the CEM detectors. Here is some detail about this
issue, from Ruth Skoug of the SWEPAM team.
> The effect of the high background counts is to cause a breakdown in
> the SWEPAM algorithm which chooses the energy range to measure.
> At times with very high background counts, the instrument always
> measures the lowest possible energy range (~250 eV to 1.8 keV).
> If the solar wind speed is sufficiently high, this energy range
> does not include the main solar wind proton beam, and SWEPAM thus
> does not measure the bulk of the solar wind particles. This condition
> was true during the Bastille Day, 2000 storm, where the peak was
> seen at energies ranging from 2 to >5 keV. The instrument is still
> happy and healthy at these times, it just looks at the wrong energies,
> and so we are unable to get solar wind moments from these data.
However, the SWEPAM instrument has another mode which measures the full
energy range (250 eV to ~17 keV) once each half hour. These data do
show the solar wind peak, and the SWEPAM team has been able to extract
moments from these data. Currently, you need to contact the team
directly to obtain these data:
Ruth Skoug - rskoug@lanl.gov
There are a few other periods of high solar activity during which the SWEPAM
instrument has exhibited the same behavior.
==============
BARTELS CYCLES
==============
Bartels cycles are a wholly arbitrary unit of time corresponding to
twenty-seven day "solar rotations". Each Bartels cycle starts at
00:00 UT and runs for exactly 27 days. Therefore, you can expect
each file to contain 27 days worth of data.
Do not confuse with Carrington rotations, which correspond to actual
solar rotations (0 to 0 degrees heliographic longitude at solar equator)
as seen from Earth.
===================
PROCESSING REVISION
===================
Occasionally, the SWEPAM team makes improvements to the moments processing
software. This results in better data.
Although the software revision is always indicated as an annotation inside
the HDF file, it is not part of the filename and hence invisible to the
casual observer.