Ulysses HISCALE Data Analysis Handbook
Appendix A: PI Comments/Explanations and Caveats
Appendix A3 (SWICS/GLG Experiment)
PI Comments/Explanations
The Solar Wind Ion Composition Spectrometer (SWICS) is using a combination of energy per charge, time of flight, and total energy measurements to separately derive mass and charge of solar wind ions in the E/q range from 0.5 to 60 keV/amu. It is described in Gloeckler et al., A&A Suppl. 92, 267, 1992.
The three parameters provided for the CDF are as follows:
a) Alpha particle density: This parameter is calculated from all triple coincidence events in the main channel with 3.5 < M < 5.1 and 1.5 < M/Q < 2.5. A (small) correction is added for counts outside this box. For background counts no correction is needed. The counts are converted to phase space densities, using efficiencies and a geometry factor from preflight calibrations. Finally, the distribution function is integrated over velocity space, i.e., over the 64 E/q values, to obtain the density (given in cm3), assuming a pencil beam angular distribution. Obviously, the alpha particle flux may be obtained by multiplying this density with the alpha particle velocity (see below). This derived parameter (the alpha particle flux) is included in the JPL CDF plots.
b) Alpha particle velocity: This parameter is obtained by calculating the zeroorder moment of the distribution function obtained as described above. Only the points in a preselected window around the maximum are used to calculate the moments. The bulk velocity is given in km s1. This parameter is not included in the JPL CDF plots.
c) Heavy ion flux: This parameter is calculated from all triple coincidence events with M > 9 and any M/Q. No background or other corrections are needed. The counts are converted to differential flux, using efficiencies and a geometry factor from preflight calibrations. The efficiencies used are a weighted average of efficiencies for the individual elements, using average solar wind elemental abundances as weights. Finally, the differential flux is integrated over E/q to obtain the total heavy ion flux, given in cm2 s1. This parameter is included in the JPL CDF plots. As all ion species flow with the same bulk velocity under most solar wind conditions, the heavy ion density may be obtained by dividing the flux by the alpha particle velocity.
a) Accuracy: The efficiencies used to derive the alpha particle density are a steep function of energy. Consequently, the integrated density is not extremely accurate, but the uncertainty should not exceed +50%. The current CDF algorithm may be improved in the future using improved efficiencies obtained by inflight calibration. The alpha particle velocity is accurate to <~10%. The absolute accuracy of the heavy ion flux is ~30%, time variations of <~20% should be real under most circumstances. Generally, the accuracy is less at very small sun aspect angle (<4 degrees).
b) Timing: The SCET time given in the SFDU header of the CDF record indicates the start time of the cycle during which the three parameters were calculated, i.e., during the following 13 minutes (or 26 or 52 minutes, depending on bit rate; see Appendix 4).
c) Zero and negative values: The CDF algorithm occasionally produces a zero or a negative number (999 to 993) for some or all of the above parameters. These numbers are a feature of the algorithm and for GLG use only; they indicate that a given parameter could not be computed in the current cycle. The user should treat these values like data gaps.
d) Data gaps: Only complete cycles are analyzed by the CDF algorithm. Therefore, even a very short data gap in the EDR stream produces a gap of at least 13 minutes in the CDF. Thus the data coverage may appear worse than it really is, if judged by the CDF alone.
Dr. Rudolf von Steiger,
Physikalisches Institut, University of Bern, Sidlerstrasse
5, 3012 Bern (Switzerland)
Phone: ++41 (0)31 65 44 19;
Fax: ++41 (0)31 65 44 05
Email: 20579::49203::vsteiger
12 July 1993
Next: Appendix A4 (HISCALE/LAN Experiment)
Return to Appendix 3 Main Table of Contents Page
Return to Ulysses HISCALE Data Analysis Handbook Table of Contents
Updated 8/8/19, Cameron Crane
QUICK FACTS
Mission End Date: June 30, 2009
Destination: The inner heliosphere of the sun away from the ecliptic plane
Orbit: Elliptical orbit transversing the polar regions of the sun outside of the ecliptic plane