POLAR TIMAS

K2 Mass Spectral Data Product

Available for the interval from March 17, 1996 through May 31, 2006

General

The TIMAS instrument compresses energy-mass-angle data acquired on the spacecraft into a series of data products that are telemetered to the ground. The various data products are described in section 4.1 of the instrument paper. The mass spectral data product consists of 64 mass steps covering the full detector range, for each of 6 large solid angles, for 8 selected energy steps. The data product is accumulated for 2, 4, 8, 16, or 32 spin (6 s) periods. Because of telemetry restrictions only selected data products were telemetered to the ground.

The 6 angular bins cover the full instrumental range and nearly 4pi steradians. Two of the look directions are centered on the spacecraft spin axis. For the first part of the mission, the spin axis was orbit normal and the pitch angles sampled in these look directions are near 90 degrees. The other 4 look directions are in the spin plane. Data are de-spun on board based on the spin rate and time of the "sun pulse". The digital data product provides the center pitch angle of each of the 6 look directions and an estimate of the variation of the pitch angle during the accumulation time

Mass spectral data were the primary data used in the preparation of the following publications:

• Polar/TIMAS Statistical Results on the Outflow of Molecular Ions From Earth at Solar Minimum, O.W. Lennartsson, H.L. Collin, W.K. Peterson, and E.G. Shelley, Advances in Space Research, 25, 2417, 2000.
• A Statistical Comparison of the Outflow of N2+, NO+, and O2+ Molecular Ions with that of Atomic O+ Ions using Polar/TIMAS Observations, O.W. Lennartsson, H.L. Collin, A.G. Ghielmetti, and W.K. Peterson, Journal of Atmospheric and Solar-Terrestrial Physics (JASTP), 62, 477, 2000.

Browse data

24 hour summary mass spectral data displays are available from a calendar or a date driven interface.

A description of the data presented in these summary plots is available here

Digital Data

files of 24 hours of digital mass spectra data are available on the TIMAS web pages. The data are in NASA's Common Data Format (CDF).

The CDF are described in a CDF skeleton table that includes the following variables:

• "Center_Epoch" Center time of data accumulation intervals in a CDF specific double precision format.
• "Start_Epoch" Begin time of data accumulation intervals.
• "Stop_Epoch" Stop time of data accumulation intervals.
• "Mass_Spectra" An array of counts per mass step for each data accumulation interval. The array has dimensions for
• 6 angular accumulation bins covering the full angular range of the instrument. The pitch angles sampled in each of these bins is given by the "Pitch_Angles" variable and associated quality parameters described below.
• 8 energy step bins. The measurement energies associated with each energy step are mode dependent. They are given by the "Energy" variable and associated quality parameters described below.
• 64 mass steps. The position of H+, He++, He+, O+, N0+, and other species in mass step space depends on the MS ELUT (Mass Spectra Energy Look Up Table) which is mode dependent. MS ELUT's are specified for each TIMAS mode. The TIMAS mode is identified by the "ICP" data variable described below..
• "Energy" An array of 8 energies (in eV) giving the center energies of the data in the "Mass_Spectra" variable in each of the 8 energy step bins for each accumulation interval.
• "Upper_Energy" An array of 8 energies (in eV) giving the upper energies of the data in the "Mass_Spectra" variable in each of the 8 energy step bins for each accumulation interval.
• "Lower_Energy" An array of 8 energies (in eV) giving the lower energies of the data in the "Mass_Spectra" variable in each of the 8 energy step bins for each accumulation interval.
• "Energy_Status" A quality parameter. 0:All data from the same instrumental energy step. 1: Data have been accumulated from multiple instrumental energy steps. 99 and 255: Invalid data.
• "Energy_LUT" A two digit number identifing the MS ELUT that determines which 8 of the 28 possible TIMAS energy steps are mapped to the 8 energy bins in the "Mass_Spectra" variable. MS ELUT's are specified for each TIMAS mode. The TIMAS mode is given by the "ICP" data variable described below.
• "Pitch_Angles" An array of 6 pitch angles (in degrees) giving the pitch angle at the center of each of the 6 rather large angular accumulation bins in the "Mass_Spectra" variable.
• "PA_Status" A quality indicator of the "Pitch_Angles" variables for each accumulation interval. 0: Valid pitch angles, 4: Pitch angle data compromised because of no "spin lock." 10: insufficient data to calculate pitch angle. 99: Invalid pitch angles. 100: No magnetometer data (required to calculate pitch angle.)
• "PA_Drift" An array of 6 angles (in degrees) giving the change in magnitude of the pitch angle at the center of each angular accumulation bin over each accumulation interval.
• "Mass" Numbers from 0 to 63 giving the mass step number for each of the 64 mass steps in the "Mass_Spectra" variable.
• "ICP" A two digit number indicating the TIMAS operating mode.
• "Energy_Range_ID" A variable indicating which of the three TIMAS energy range modes was active at the time of data acumulation. 0: Data for the full (15eV to 33 keV) energy range was acquired. 1: Data for a reduced (15 eV to 25 keV) energy range was acquired. 2: Data were sampled only for the lowest energies. Data acquired in this mode has not been validated.
• "FEC" Total fast event counter counts as described in section 4.1.1 of the TIMAS instrumentation paper.
• "BCR" Total background counts per spin as described in section 4.1.2 of the TIMAS instrumentation paper.
• "SPINS" Number of 6 second spin periods in the accumulation interval for the "Mass_Spectra" variable.
• "Quality" A 2 digit quality number for the "Mass_Spectra" variable. 0: OK, 1: Some data missing; 5: Some warning flags were set. 99: No valid data. 0 and 1 indicated high quality data.

The following Orbit data are included in the digital files.

• "Orbit_Status" A quality number for the orbital data. 0: OK, 99: Orbit data not available.
• "L" The MacIlwain L parameter associated with the "Center_Epoch" of the data accumulation interval.
• "MLT" The magnetic local time associated with the "Center_Epoch" of the data accumulation interval.
• "Ltime" The local time associated with the "Center_Epoch" of the data accumulation interval.
• "RE" The geocentric distance (in units of Earth radii) of the polar satellite associated with the "Center_Epoch" of the data accumulation interval.
• "Mlat" The magnetic latitude (in degrees) associated with the "Center_Epoch" of the data accumulation interval.
• "INVL" The invariant latitude (in degrees) associated with the "Center_Epoch" of the data accumulation interval.

The following variables in the digitial files contain no data.

• "Omni_Mass_Spectra"
• "Look_Directions" Normal operations have the angular accumulation bins for the "Mass_Spectra" variable fixed in "Fixed Platform" coordinates. The 6 look directions in FP coordinates are: 1: in the + Z (spin axis) direction, 2: in the +X direction, (in the spin plane, in the direction closest to the sun direction. 3: +Y direction (completing a right hand coordiante system) 4: -X direction. 5: -Y direction, and 6: -Z (spin axis) direction. For the first part of the mission the spin axis was orbit normal and so the +/- Z axes sampled mostly near 90 degree pitch angles. Later in the mission the spin axis was pointed nearly normal to the ecliptic.

Caveats

• The data in the "Mass_Spectra" variable are in counts per accumulation interval. Conversion to flux units requires a detailed understanding of the detector system described in the TIMAS instrument description
• Data are available for most, but not all, days between March 17, 1996 and May 31, 2006. Data are missing for several reasons including: TIMAS high voltage off, Magnetometer key parameter data are not availble to calculate pitch angles, and a problem with telemetry described below..
• On December 8, 1998 the TIMAS instrument suffered a high voltage breakdown that significantlty reduced the instrumental sensitivity. After this time the instrumental response to ions with energies less than ~800 eV is extremely weak and non linear.
• From November 1999 through March 30, 2001, TIMAS data were intermittent because of an intermittent connection in the telemetry lines on the satellite. The problem was resolved with a shift to the redundant telemetry system on March 30, 2001.

Diagnostic Code

A diagnostic code written in the Interactive Data Language using tplot developed by Davin Larsen at UC Berkeley is available.

The diagnostic code generates both line plots and mass spectra.

Return to TIMAS main page

Prepared by WK (Bill) Peterson, March 19, 2010.