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. ---------------------------------------------------------- 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. ----------------------------------------------------------------------------------- Related data and directories: SPDF Data and Orbits Services -------------- SPDF Contact: Natalia Papitashvili , Please acknowledge NASA's Space Physics Data Facility for data usage. Authorizing NASA Official: Dr. R.E. McGuire, Head, SPDF, NASA Goddard Space Flight Center 301-286-7794, e-mail: Robert.E.McGuire@nasa.gov -----------------------------------------------------------------------