1. The description of the parameters included in the tape, and the CDF plots: The data provided in the CDF are the proton velocity, density, and temperature. In the data provided on CDROM/magnetic tape, the velocity components are in spacecraft­based X,Y,Z coordinates, whereas for the CDF plots the velocities are provided in RTN coor  dinates.

Definition of X,Y,Z coordinates:

Z is a vector along the spin axis towards Earth, X is a vector lying opposite to the direction of the sun sensor (i.e., the azimuth the experiment is in when the cycle starts), and Y is a vector completing a right­handed system. The spacecraft rotates counterclockwise as viewed from Earth. Thus, x,y,z track where the entrance aperture of our sensor is with time. WARNING: Note that the definition of the X and Y vectors is opposite in sign to that chosen by the magnetometer team for their data!!!!!

Definition of RTN coordinates:

R is a unit vector along the Sun­spacecraft line. T is Omega x R, where Omega is a unit vector along the Sun's rotation axis. N = R x T.

2. Appendix A: Instrument and CDF Algorithm Specifics.

The SWOOPS ion analyzer measures 3­d velocity space distributions of positively­charged ions. In its normal solar wind mode, the instrumental energy range is 0.25 to 12 keV/Q; active energy tracking allows for fine energy spacing within a smaller range which is ample for characterization of the thermal proton and helium distributions. Each spectrum takes 2 minutes to accumulate, but telemetry takes longer. A spectrum is telemetered to the ground in 4 minutes at highest bit rate; at lower spacecraft bit rates the time increases proportionately. Data are provided to the CDF with approximately half hour temporal resolution. This analyzer does not make an explicit ion species determination; separation of protons from doubly­charged helium is enabled by the fact that the two species have similar convection speeds.

CDF parameters are calculated by numerical integration of velocity­weighted ion distributions over an E/q range chosen to include the thermal proton population but not the alpha particles. Under extremely hot conditions, there can sometimes be some overlap between these populations.

Many other proton and helium output products are available. Full time­resolution data are also available, with a typical spectral repetition period of 4 minutes (tracking) or 8 minutes (playback). Electron data can also be made available. Contact the PI for these products.

PI Caveats

The ion temperature may be overestimated when the solar wind gets exceptionally cold. This is due primarily to the angular spacing of the measurements being further apart than the beam width at larger radial distances. The PI team has some data products that partly alleviate this problem (temperature based upon an energy spectrum taken using only the width in the energy direction). The team is currently (Oct., 1993) working on a least squares fitting technique that should further improve results in this regard. In general, it is recommended that users who need reliable, quantitative, temperatures visit the APL Ulysses website:

http://sd-www.jhuapl.edu/Ulysses/index.html

Information supplied by:

Dr. Bruce E. Goldstein, Mailstop 169­506, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 (USA) 
Tel. +1 818 354­7366; Fax: +1 818 354­8895 
E­mail: JPLSP2::BGOLDSTEIN

29 October 1993

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