https://spdf.gsfc.nasa.gov/pub/data/imp/imp8/plasma_mit/sw_msheath_min/
aareadme.txt
NSSDC provides these data as annual files.
(They are accessible from MIT
ftp://space.mit.edu/pub/plasma/imp/fine_res/ but in shorter files ).
The contents/format of records are:
Wd Format Fill values Parameters
1 I5 9999 Year
2 I4 999 Doy
3 I3 99 Hour
4 I3 99 Minute
5 I3 99 Second
6 I2 9 Spacecraft Flag (IMP8=8)
7 F14.7 99999.9999999 Decimal Year
8 I2 9 Region Flag
9 I2 9 Operating Mode Flag
10 F8.2 9999.00 X, Re, GSE
11 F8.2 9999.00 Y, Re, GSE
12 F8.2 9999.00 Z, Re, GSE
13 F8.2 9999.00 Y, Re, GSM
14 F8.2 9999.00 Z, Re, GSM
15 F7.1 9999.0 V_mom, km/sec.
16 F7.1 9999.0 V_fit, km/sec.
17 F7.1 9999.0 Proton V_thermal_mom, km/sec.
18 F7.1 9999.0 Proton V_thermal_fit, km/sec.
19 F7.1 9999.0 Proton Density_mom, n/cc
20 F7.1 9999.0 Proton Density_fit, n/cc
21 F7.1 9999.0 E/W flow angle_mom,deg.
22 F7.1 9999.0 E/W flow angle_best,deg.
23 F7.1 9999.0 Flow elevation_thresh, deg.
24 F7.1 9999.0 Flow elevation_threshsp, deg.
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The following material has been copied from the MIT web site -
DESCRIPTION OF RECORDS
1) In the eighth field of each record, a flag ("rg") has been written indicating
our estimate of the region from which the data came.
There are three flag values:
1 This time is definitely solar wind.
2 This time is either solar wind or magnetosheath, with no differentiation
being made. This designation is used for multiple crossings between the
solar wind and sheath regions.
3 This time is definitely NOT solar wind, being either magnetosheath or
magnetospheric data.
2) The ninth field "md" indicates the operating mode of the experiment. See
the detailed descriptions in the ADDITIONAL COMMENTS section below.
3) The parameter values: our 'better' parameters are in
the right column of each two-column pair. The left column of the pair shows
parameters usually derived from taking moments of the distributions. As can
be seen easily by eye, there is some discrepancy between moments and our
best parameters; moments are definitely less accurate.
All parameters may be accessed (with subsetting and graphical
browse functionality) at
http://nssdc.gsfc.nasa.gov/ftphelper/imp_mit_min.html
Graphical plotting capabilities for all IMP experiments are available at
http://nssdc.gsfc.nasa.gov/ftphelper/
Use moment values with caution, and PLEASE request assistance or clarification.
For the moment parameters, changes in value are more trustworthy than
absolute values, but nothing is guaranteed to be accurate.
A value of 9999.0 means that we couldn't calculate that parameter. All
parameters are based on a convected, isotropic Maxwellian model.
We recommend that, in the absence of data other than moment values, you try
to obtain the IMP 8 LANL experiment plasma values as well at
http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/imp8_lanl_2m.html
4) We use the convention Jan. 1 = DOY 1. Please note that the decimal
year is double precision, e.g. 1994.xxxxxxx where xxxxxxx is fraction
of year.
5) Speeds and thermal speeds are given in km/s. Effects due to the
orbital motion of Earth are removed from the better parameters, but not from
the moment parameters (see note 7).
6) Thermal speed is the most probable thermal speed (i.e., the square
root of [2kT/m(proton)]). To convert thermal speed to temperature in
eV, multiply 0.0052 by the square of the thermal speed; to convert to temperature
[K], multiply the square of the thermal speed by 60.5 .
This is probably the most inaccurate moment parameter, since moments tend to
underestimate the temperature in cold distributions.
7) The angles are in degrees. Azimuth is E/W, meaning bulk flow from
the East or the West side of the Sun respectively, while flow elevation is
from North or South of the s/c spin plane (almost identical to the plane of
the ecliptic). For signs, positive azimuth angle means flow from the W;
positive elevation angle means flow from the S. If we don't get good angles,
there won't be get any velocity components; speeds are available in some
such cases. The aberration in velocity due to Earth's motion around the Sun
has been removed from the best (and threshsp) values, but not from the moment
values (see note 8).
"Threshsp" values are determined from currents greater than a threshold
value, below which we are not confident about the contribution of noise.
Dr. Joseph King (GSFC) has looked at 27-day averages of OMNIWeb data from 1984-1994.
He finds (and we agree) that there is an offset of about +2 degrees (from the South)
in the N/S angle and an annual variation of that angle with an amplitude of about 1
degree. We believe that the annual variation is due to a tilt of the s/c spin axis.
He found the mean flow longitude in that study to be -0.3 degrees with no obvious
annual variation.
8) The moment values, for angles and for the speed, do NOT
have aberration corrections included. This means that the total
speeds are slightly too low, and that the angles are not really
correct. In particular, the azimuthal (E/W) angle is about 4 degrees
too positive; this can clearly be seen where both nonlinear and moment
angles are available.
9) The spacecraft trajectory values (xse, yse, zse, ysm, zsm) are in
units of Earth radii.
10) For papers and presentations using these data, please acknowledge
that you received them from the MIT Space Plasma Physics Group. Please
feel free to contact us if you have questions about any parameters.
11) Please send us a copy of papers, presentations, et cetera using
these data.
12) If you have any questions, please contact
Ms. Pamela A. Milligan pam@space.mit.edu
Dr. Alan J. Lazarus ajl@space.mit.edu
Dr. John Richardson jdr@space.mit.edu
ADDITIONAL COMMENTS
13) IMP 8 spins with a period of approximately 2.7s. The Faraday Cup (FC)
instrument scans the solar wind distribution stepping through a contiguous set of
energy windows, one step per spacecraft spin. The FC instrument divides the spin
into thirty-two, 11.25 degree angular sectors and integrates the measured
currents over different angular sectors depending upon the Mode in which the
instrument is operating. The border between two of the 11.25 degree angular
sectors lies on the Sun-spacecraft line.
14) The FC sensor collector plate is divided into two, semi-circular halves; the
division line is parallel to the spacecraft spin plane which is approximately
parallel to the ecliptic plane. The split collector allow determination of
the bulk plasma flow relative to the spin plane; North/South angles refer to
flows coming from above or below the spin plane respectively (flows from the
South are designated as having a positive N/S angle).
The bulk flow angle in the spin plane is determined from the measurements of
current vs. rotation angle. The currents telemetered to the ground are the
sums of currents for the two half-collectors ("A" and "B"} and, for the TMS and
AQM modes, also the current for the half-collector "B".
Electrons are measured except for the eight angles near the Sun.
15) The following Table describes the measurements for each mode.
MODE NAME ANGLES number,[deg] CURRENTS ENERGY WINDOWS MEASURED
Number Protons Electrons
2 Tracking (TMS) eight, 11.25 centered A+B and B 8* 4
on Sun-s/c line
six, 45 for remainder
of spin
3 Acquisition (AQM) same as TMS same as TMS 24 21
1 Non-tracking (NTMS) eight, 45 A+B only 24 21
__________
*Selected so that the peak flux energy step of the prior distribution is the 3rd step
of this measurement.
Note that the mode names are historical and confusing: the NTMS mode has the
greatest sensitivity because of the 45 degree angular sectors and hence longer
integration times, but all the energy windows won't fit into the working side
of our on board memory. So all the parameters will be in modes 2 or 3. In order
to reduce the time between spectra, in the TMS mode the eight lowest electron
energy windows are covered using four sets of two windows of increasing energy;
those eight electron windows are thus covered in a sequence of four TM spectra.
16) The experiment has two memories only one of which is operating perfectly. As
a result, only every other TMS spectrum is usable, and the time between spectra
is usually twice that that would be expected from the spacecraft spin rate. The
bad half-memory also limits the energy windows that can be used in the other
modes, since they require both memories to hold the data. On occasion, the data
are read out rapidly enough by the spacecraft to allow repeated use of the good
half-memory, and the time resolution in the TMS is approximately 32 seconds.
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