<00readme_themisb.txt> by Joe King and Natalia Papitashvili, December 15, 2010 This data set contains ARTEMIS P1(THEMIS B) plasma parameters from the Electrostatic Analyzer (ESA), magnetic field data from the FGM instrument, and geocentric and selenocentric spacecraft position data. The data are at 96s or 384s resolution, each for several contiguous hours for most days. The data set, and a companion from ARTEMIS P2(THEMIS C), are from September, 2010, and later, when these two spacecraft were in the vicinity of the moon. These data sets were created at NASA/GSFC/SPDF under the NASA/LASER-funded Lunasox project. See http://themis.ssl.berkeley.edu/index.shtml for details on the THEMIS spacecraft, instruments and data. Achieving this required: 1. Retrieval of CDF files from CDAWeb of of ESA L2 "good" quality, "full mode," ion plasma data [density (N), thermal speed(W), flow velocity GSE Cartesian components(Vx,Vy, Vz)], starting 9/1/2010 when the spacecraft are mostly in the moon's vicinity. "Full mode" means as determined from 3-sec high-angular-resolution distributions taken once every 96s (Fast Survey Scan - FSS) or 384s (Slow Survey Scan - SSS), where FSS and SSS are mutually exclusively used for several contiguous hours during each of most days. Data retrieval was followed by creation of ASCII version with N, W, and Vi, and with |V|(flow speed) as computed by us from the Vi. 1a. Despike the plasma data. A modest number of ESA L2 data points appear to be single-point spurious spikes. We have attempted to delete these as follows. We test a point using its two predecessors and two followers. We require that the 1st and last of these 5 points be within 60 mins of each other. The first two and last two points in a data segment separated from its neighbors by intervals of >60 min go untested by the algorithms discussed here. We visually scanned output data looking for obvious spikes thereby missed, and deleted these. Any record having a declared spike in any of its physical parameters is rejected. For a parameter value to be declared a spike, it must satisfy two criteria. Let P represent the value of the physical parameter being tested. Define

as the mean value of parameter P over the 1st, 2nd, 4th, and 5th points of the current set, and let sigma(P) be the RMS deviation in this average. The first test for a spike is to have |P-

| > 20 * sigma(P). As the second test, for P = V, Vi (i = x, y, z), N, W, we require |P-

| > k *

where k = 0.1, 0.1, 0.3, 0.6 for P = V, Vi, N, W respectively. For Themis B and C, these tests eliminated 64 and 51 96s or 384s ESA L2 points, respectively, over the interval September 3, 2010 - January 29, 2011. 1b. In addition to retrieving ESA N, W and Vi values from CDAWeb, we also retrieved the ESA ion mode flag, where the values are 0 and 1. Zero denotes a magnetospheric mode and one a solar wind mode. The magnetosphere mode involves taking measurements over much broader ranges in energy and look direction than for the solar wind mode. This optimizes observations of hot, subsonic non-solar wind plasma and of cooler supersonically flowing solar wind plasma. Usually, but not always, ESA had been set to the solar wind mode when the spacecraft was in the solar wind. But starting in September, 2011, the mode was kept as magnetosphere. In general, plasma densities and flow speeds, but not flow directions and temperatures, of ESA magnetosphere-mode data taken while the spacecraft was in the solar wind are reliable. For further details, see the ESA documentation accessible through the UCB URL given above. (Updated, March, 2012) A list of intervals, of hourly resolution, when THEMIB-B was in the solar wind is given at https://omniweb.gsfc.nasa.gov/ftpbrowser/themis_b_sw.txt. 1c. Moments become unreliable in the presence of sufficiently high fluxes of solar energetic particles. Examples are seen at January 23-24 and 27-29, 2012. From Jim McFadded of the ESA team: SEP events will cause high background which will distort the moment calculation -- its like adding an isotropic component that is not drifting -- density,pressure goes up and velocity goes down. You need a background subtraction routine to recover moments on the ground if you want to correct this. (March, 2012) 2. Retrieval of 1-min spacecraft position (GSE) data from SSCWeb 3. Retrieval of 1-min lunar position (GSE) data from SSCWeb 4. Using of moon-centered 1-min spacecraft positions by taking differences between the geocentric spacecraft and moon positions, and changing units from Re to Rm (Moon radii, = 1737 km). 5. Merger of geocentric and selenocentric spacecraft position data and plasma data, interpolating the 1-min position data to the times of the plasma data 6. Retrieval of CDF files of 3-sec magnetic field FGM data in GSE coordinates from CDAWeb and conversion to ASCII. 7. Merger of plasma/position data and magnetic field data. To each 96s or 384s plasma/position record, we add the 3-s magnetic field data whose time tag is closest to that of the plasma data (because, as noted above, the plasma parameters are based on high-angular- resolution ion plasma distributions each determined over three seconds. 8. Creation of FTPBrowser interfaces to these data for (a) plots and listings [https://omniweb.gsfc.nasa.gov/ftpbrowser/themisb_mrg.html] and (b) parameter value occurrence distributions and other statistics, with filtering [https://omniweb.gsfc.nasa.gov/ftpbrowser/themisb_mrg_d.html]. The plots are all in a time-series format (parameters vs. time). In order to see the selenocentric orbits in XY, XZ and YZ projections go to SPDF's 4-D Orbit Viewer page at http://sscweb.gsfc.nasa.gov/tipsod/ The contents of each of the merged records - WORD FORMAT MEANING UNITS/COMMENTS 1 I4 Year 1998,1999, etc. 2 I4 Decimal Day January 1 = Day 1 3 I3 Hour 0,1,...,23 4 I3 Minute 0,1,...,59 5 F7.3 Seconds 6 F8.2 Field Magnitude Average |B| 1/N SUM |B|, nT 7 F8.2 BX GSE-Coordinate System nanoteslas 8 F8.2 BY GSE-Coordinate System nanoteslas 9 F8.2 BZ GSE-Coordinate System nanoteslas 10 F7.2 Plasma Ion density n/cc 11 F7.1 Thermal speed km/s 12 F8.1 Plasma flow speed km/s 13 F8.1 Vx Velocity km/s 14 F8.1 Vy Velocity km/s 15 F8.1 Vz Velocity km/s 16 F9.3 X GSE Re 17 F9.3 Y GSE Re 18 F9.3 Z GSE Re 19 F9.3 X SSE Rm 20 F9.3 Y SSE Rm 21 F9.3 Z SSE Rm ------------------------------------------------------------------ Related data and directories: http://lunasox.gsfc.nasa.gov/ SPDF Data and Orbits Services SPDF Contact: Natalia Papitashvili , Please acknowledge the Space Physics Data Facility at NASA/GSFC for data usage. Authorizing NASA Official: Robert Candey, Head, SPDF, NASA Goddard Space Flight Center e-mail: Robert.M.Candey@nasa.gov ------------------------------------------