Revised Version: 2004-07-27, Section 8 on PI contact information
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USERS GUIDE FOR ULYSSES SWOOPS DATA FROM THE JUPITER ENCOUNTER

                             TABLE OF CONTENTS

1. OVERVIEW OF THE SWOOPS EXPERIMENT
2. MEASUREMENTS AT JUPITER
3. THE SWOOPS ELECTRON EXPERIMENT
4. DATA REDUCTION ALGORITHMS
5. BOUNDARIES AND TRANSITIONS OBSERVED DURING THE ENCOUNTER
6. DESCRIPTION AND FORMAT OF DATA SUBMITTED TO THE NSSDC
7. DATA CAVEATS
8. FURTHER INFORMATION

1. OVERVIEW OF THE SWOOPS EXPERIMENT

The SWOOPS (Solar Wind Observations Over the Poles of the Sun) experiment has
two electrostatic analyzers, one for positive ions and one for electrons. The
instrument is fully described in: The Ulysses Solar Wind Plasma Experiment, S.
J. Bame, D. J. McComas, B. L. Barraclough, J. L. Phillips, K. J. Sofaly, J. C.
Chavez, B. E. Goldstein, and R. K. Sakurai, Astronomy and Astrophysics
Supplement Series, Ulysses Instruments Special Issue, Vol. 92, No. 2, p.
237-265, 1992. The electron and ion analyzers are separate instruments that
operate asynchronously. 

2.  MEASUREMENTS AT JUPITER

The following publications contain descriptions of SWOOPS operations and
instrumental limitations at Jupiter:

Phillips, J.L., S.J. Bame, M.F. Thomsen, B.E. Goldstein, and E.J. Smith, 
Ulysses Plasma Observations in the Jovian Magnetosheath, Journal of 
Geophysical Research, p. 21189, 1993.

Phillips, J.L., S.J. Bame, B.L. Barraclough, D.J. McComas, R.J. Forsyth,
P. Canu, and P.J. Kellogg, Ulysses Plasma Electron Observations in the
Jovian Magnetosphere, Planetary and Space Science, p. 877, 1993.

The electron instrument functioned well throughout the encounter, subject
of course to its inherent energy limitations and to the energetic particle
background present in the magnetosphere.  The ion experiment, which
was optimized for solar wind measurements and thus has a limited field
of view, produced useful measurements in the outbound magnetosheath
only.  A summary of the ion measurements follows:

INBOUND MAGNETOSHEATH.  The look direction of the experiment was ground-
commanded, based on expectations of sheath flow direction.  During the
brief inbound sheath encounter, the flow was anomalous (sunward at times).
Thus the instrument "missed the beam" and returned no useful measurements.

OUTBOUND MAGNETOSHEATH.  Here the flow was more or less as expected.
The ion experiment captured most of the sheath flow beam during most
outbound sheath intervals.  The measurements are shown in the sheath
paper cited above.  In general, flow velocities agreed with the electron
velocities.  Disagreements occurred when the ion sensor missed the heart
of the beam.  Densities and temperatures were generally substantially
underestimated by the ion experiment due to its limited angular coverage.

MAGNETOSPHERE.  Due to the limited energy range and look direction of
the instrument, as well as the energetic particle background, the
ion instrument did not return useful data in the magnetosphere.

As a result of these problems, the SWOOPS ion observations inside the
Jovian bow shock are not included in the archived Jupiter data.  

Data provided start at the beginning of day 25 (January 25, 1992) and
run through the end of day 48 (February 17) and include all bow shock
and magnetopause crossings.  Both experiments were shut down for a 25-hour 
interval surrounding closest approach due to elevated penetrating background.

The interval specified by PDS for this encounter includes substantial intervals
of solar wind.  In general, the SWOOPS ion experiment provides superior 
characterization of solar wind density and speed in the solar wind, while
the electron experiment provided the only easily usable data inside the
Jovian bow shocks.  In order to provide the best observations for each
phase of the encounter, the following schemes were adopted:

0000 UT on Day 25 until 1200 UT on Day 33: Solar wind scheme.
Electron temperature, charge-weighted ion (proton + alpha) 
density, and proton velocity.  Ion data were averaged to coincide
with the electron spectral times.

1200 UT of Day 33 until 1200 UT on Day 47: Jupiter scheme.
Electron temperature, density, and velocity

1200 UT on Day 47 until 2400 UT on Day 48: Solar wind scheme.

The minor plasma discontinuities occurring at 1200 UT on days
33 and 47 are artifacts of the switchover between Jupiter and 
solar wind schemes.

While the solar wind ion products included in the archive are created through
routine data reduction, the electron parameters required unique Jupiter-
specific processing.  A description of the experiment and processing follows.

3. INTRODUCTION TO THE SWOOPS ELECTRON EXPERIMENT

The SWOOPS electron spectrometer is a 120-degree spherical section electrostatic
analyzer which measures the 3-d velocity space distributions of solar wind
electrons.  In the mode used at Jupiter, the instrumental energy range was
1.6 to 862 eV in the spacecraft frame.  Since the spacecraft charged to 
+2 to +44 volts during the encounter, 2 to 44 eV are subtracted from the
measured energies (electrons measured at energies below the spacecraft 
potential are electrostatically trapped photoelectrons). 

Each spectrum takes 2 minutes to accumulate, but telemetry takes longer.
During the Jupiter encounter, spectra were returned every 5.7 minutes.
The analyzer uses 7 channel electron multipliers (CEMs) to count electrons 
discretely over 95% of the unit sphere in look direction.  For telemetry 
conservation, 2 out of every 3 spectra are "two-dimensionalized" onboard the
spacecraft, that is the count rates are averaged over all 7 CEMs.  These 2-d
spectra thus return electron counts as a function of energy and spacecraft
spin angle.  The full 3-d spectra return counts as a function of energy, 
spacecraft spin angle, and polar angle (measured from the spacecraft spin
axis, which points at Earth).  The 3-d spectra incorporate 32 spin-angle 
steps, for a total spectral content of 20 energies x 32 azimuths x 7 polar 
angles, while the 2-d spectra include 20 energies x 64 azimuths x 1 angle.

4. ELECTRON DATA REDUCTION ALGORITHMS

The first step in data reduction is determination of the spacecraft potential.
This is done by identifying inflections in the angle-averaged energy spectra.
While this is automated in the solar wind, it was done by eye, spectrum-by-
spectrum, for the Jupiter encounter.  Potential averages +6 V in the solar
wind and sheath, and substantially higher in the magnetosphere.  The count
rate arrays are corrected for spacecraft potential and converted to phase-
space density arrays.

Plasma moments are then calculated by numerical integration of the velocity-
weighted ion distributions.  A total integration is performed from the
spacecraft potential (corresponding to zero energy solar wind electrons) to
the instrumental energy limit.  Since the first few eV above the spacecraft 
potential are contaminated with photoelectrons on non-radial trajectories, 
it is necessary to use a biMaxwellian fit to the lowest energy points
to fill in this part of the distribution.

The integrations produce density, temperature components, velocity, and 
heat flux.  At this time, densities, scalar temperatures, and 3-d velocity
vectors (for 3-d measurements only) are being provided for archiving.  

5. BOUNDARIES AND TRANSITIONS OBSERVED DURING THE ENCOUNTER

The following boundaries and regions were identified by the SWOOPS experiment
team (see the papers cited above for details):

Day	Time	Feature
----------------------------------------------------------------
33	1733	Cross bow shock (BS) into magnetosheath
33	2222	Cross magnetopause (MP) into boundary layer (BL)
33	2308	Enter magnetosphere
34	1655	Enter BL
34	1720	Cross MP into sheath
34	1945	Cross MP into BL
35	0025	Cross MP into sheath
35	0100	Cross MP into BL
35	0125    Cross MP into sheath
35 	0250	Cross MP into BL
35	0400	Enter magnetosphere
38	1132	Enter open field region
38	1335	Enter magnetosphere
38	2137	Enter open field region
38	2310	Enter magnetosphere
39	0054	Last usable data before shutdown
40	0152    First usable data after shutdown
40	1126	Enter open field region
40	1232	Enter magnetosphere
40	2125	Enter open field region
40	2241	Enter magnetosphere
43	0024	Enter BL
43	0100	Enter magnetosphere
43	1058	Enter BL
43	1226	Enter magnetosphere
43	1337	Enter BL
43	1357	Cross MP into sheath
43	1700	Cross MP into BL
43	1740	Enter magnetosphere
43	1820	Enter BL
43	1910	Cross MP into sheath
45	0037	Cross BS into solar wind
45	0428	Cross BS into sheath
45	0933	Cross MP into BL
45	1030	Enter magnetosphere
45	1400	Enter BL
45	1600	Enter magnetosphere
45	1815	Enter BL
45	1825	Enter magnetosphere
45	2045	Enter BL
45	2140	Cross MP into sheath
47	0753	Cross BS into solar wind	

6. DESCRIPTION AND FORMAT OF DATA SUBMITTED TO THE NSSDC

The data provided to the NSSDC are the total charge density (electron or
charge-weighted ion), electron temperature, and plasma (electron or 
proton) velocity.  Electron data were integrated over the full instrumental 
energy range but not extrapolated to higher energies.  Spacecraft position is
also provided. The times specified in the file are the centers of each 
2-minute spectrum.

The data file was created with Fortran on a Vax running VMS.  It can
be opened and read as follows:

      open (3, file='JUPITER_ELECTRONS.DAT', status='old',recl=151)

c      iyr           - year
c      idoy          - day of year (Jan 1 = 001)
c      ihr           - hour, UT
c      imin          - minute, UT
c      isec          - second, UT
c      idim          - dimension of electron spectrum (2 or 3)
c      rj	     - Jupiter-spacecraft distance, Rj
c      xlat          - Jovigraphic latitude of spacecraft, degrees
c      xmlat	     - magnetic latitude of spacecraft, degrees
c      lt	     - local time of spacecraft, hhmm
c      density       - charge density per cubic cm
c      temp          - electron temperature, Kelvins
c      vx,vy,vz	     - plasma bulk velocity, in km/s in XYZ system
c      vr,vtheta,vphi- plasma bulk velocity, in km/s in spherical system

      read(31,88)
     >    iyr,idoy,ihr,imin,isec,idim,rj,xlat,xmlat,lt,
     >    density,temp,vx,vy,vz,vr,vtheta,vphi

88    format(1x,i2,1x,i3,3(1x,i2),1x,i1,f8.3,2f8.2,i5.4,8e13.5)

Velocity components are flagged (1.e32) for 2-d spectra when Jupiter
scheme is in use.

The following coordinate systems are used:

1.  XYZ is a Jupiter-centered cartesian system with solar longitude
fixed.  Z is northward along the planetary rotation axis, X is perpendicular
to Z in the plane containing Z and the Sun-Jupiter line, positive 
antisunward, and Y completes the right-handed set, positive dawnward.

2. Spherical is a standard spherical system based on the Jupiter-centered
spacecraft position, with R positive outward, Theta positive in a southward
sense, and Phi positive in the sense of planetary rotation.

7. DATA CAVEATS

In the magnetosphere, a very simple scheme was used for background rejection.
The lowest count rate for a given spectrum was subtracted from all pixels
in that spectrum.  Thus any changes in background during the course of
a 2-minute spectra accumulation time are not accounted for.  While the
resulting plasma densities were corroborated by comparison with the plasma
frequency-based densities from the URAP experiment (see magnetosphere
paper cited above), the possibility exists that some roll-modulated 
background exists and distorts the plasma velocities.  At the time of 
this submission, the velocities provided are the best values available.
However, the SWOOPS team is actively pursuing a roll-modulated background
rejection scheme, and the data will be updated as appropriate.  The
user should be cautious in interpreting the electron velocities.

During the intervals indicated as open field regions in the listing
above, there are significant uncertainties in all plasma parameters.
This is due to uncertainties in the spacecraft potential.  While it
is clear that the densities are relatively high and the temperatures
are low in these regions, small errors in spacecraft potential can
create large errors in all derived plasma parameters.  These values
will be updated as the SWOOPS team research into the open field regions
continues.

The spacecraft ephemeris was provided by the Ulysses project at high
resolution during the encounter proper.  Far from the planet (i.e. the
beginning and ending of the SWOOPS data file), the ephemeris resolution 
was coarser, and you will see large steps in spacecraft position in the 
SWOOPS data file.  Higher-resolution position information may be available 
through the PDS.

8. FURTHER INFORMATION

For information on this data set and on acquiring other types of data not 
provided to the NASA Planetary Data System or NSSDC, contact the SWOOPS 
Principal Investigator, Dr. David J. McComas, at Southwest Research Institute, 
dmccomas@swri.edu, 210-522-5983. For information on the reduction and analysis 
of data from the positive ion experiment, contact Dr. Bruce E. Goldstein at 
the Jet Propulsion Laboratory, bgoldstein@jplsp2.jpl.nasa.gov, 818-354-7366.