Ulysses SWOOPS High Resolution Plasma Data Description
Ulysses SWOOPS - Solar Wind Observations Over the Poles of the Sun Bundle
PDS3 DATA_SET_ID = ULY-J-SWOOPS-5-RDR-PLASMA-HIRES-V1.0
ORIGINAL DATA_SET_NAME = ULY JUP ENCOUNTER SWOOPS PLASMA
HIRES-V1 DATA
START_TIME = 1992-01-25T00:07:16.000
STOP_TIME = 1992-02-17T23:56:31.000
PDS3 DATA_SET_RELEASE_DATE = 1998-05-01
PRODUCER_FULL_NAME = JOHN L. PHILLIPS
Collection Overview
===================
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 electron and ion analyzers are
separate instruments that operate asynchronously.
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 switch-over 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.
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.
Processing
==========
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
Data
====
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='SWOOPS.TAB', status='old', recl=151)
c time - spacecraft event time in the format
c yyyy-mm-ddThh:mm:ss.sssZ
c idim - dimension of electron spectrum (2 or 3)
c rj - Jupiter-spacecraft distance, Rj
c xlat - Jovigraphic latitude of spacecraft,
c degrees
c xmlat - magnetic latitude of spacecraft,
c 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
c system
c vr,vtheta,vphi - plasma bulk velocity, in km/s in
c spherical system
read(31,88)
❯ time,idim,rj,xlat,xmlat,lt,
❯ density,temp,vx,vy,vz,vr,vtheta,vphi
88 format(a24,1x,i2,1x,f8.3,2(1x,f8.2),1x,i4,8(1x,e11.4))
Velocity components are flagged (-9.9999e+10) for 2-d spectra
when Jupiter scheme is in use.
Coordinate System
=================
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 anti-sunward, 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.
Data Coverage and Quality
=========================
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.
References:
===========
Bame, S.J., D.J. McComas, B.L. Barraclough, J.L. Phillips, K.J.
Sofaly, J.C. Chavez, B.E. Goldstein, and R.K. Sakurai, The
Ulysses solar wind plasma experiment, Astron. Astrophys. Suppl.
Ser: 92, 237-265, 1992.
Bame, S.J., B.L. Barraclough, W.C. Feldman, G.R. Gisler, J.T.
Gosling, D.J. McComas, J.L. Phillips, and M.F. Thomsen,
Jupiter's Magnetosphere: Plasma Description from the Ulysses
Flyby, Science, 257, 1539, 1992.
(https://doi.org/10.1126/science.257.5076.1539)
Hammond, C.M., J.L. Phillips, S.J. Bame, and E.J. Smith, Ulysses
Observations of the Planetary Depletion Layer at Jupiter,
Planet. Space Sci., 41, 853, 1993.
(https://doi:10.1016/0032-0633(93)90093-H)
Hoogeveen, G.W., J.L. Phillips, and M.K. Dougherty, Ulysses
observations of corotation lags in the dayside Jovian magnetosphere:
An evaluation of the hinged magnetodisc and magnetic anomaly models,
J. Geophys. Res., 101, A10, 21439-21446, 1996.
(https://doi.org/10.1029/96JA02042)
Lin, N., P.J. Kellogg, J.P. Thiessen, D. Lengyel-Frey, B.T.
Tsurutani, and J.L. Phillips, Whistler Mode Waves in the Jovian
Magnetosheath, J. Geophys. Res., 99, 23527, 1994.
(https://doi.org/10.1029/94JA01998)
Moldwin, M.B., E.E. Scime, S.J. Bame, J.T. Gosling, J.L.
Phillips, and A. Balogh, Plasma Electron Signatures of Magnetic
Connection to the Jovian Bow Shock: Ulysses Observations,
Planet. Space Sci., 41, 795, 1993.
(https://doi:10.1016/0032-0633(93)90087-I)
Phillips, J.L., S.J. Bame, M.F. Thomsen, B.E. Goldstein, and E.J.
Smith, Ulysses Plasma Observations in the Jovian Magnetosheath,
J. Geophys. Res., 98, 21189, 1993.
(https://doi.org/10.1029/93JA02592)
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, Planet. Space Sci.,
41, 873, 1993.
(https://doi.org/10.1016/0032-0633(93)90095-J)
Prange, R., P. Zarka, G.E. Ballester, T.A. Livengood, L. Denis,
T. Carr, F. Reyes, S.J. Bame, and H.W. Moos, Correlated
Variations of UV and Radio Emissions During an Outstanding Jovian
Auroral Event, J. Geophys. Res., 98, 18779, 1993.
(https://doi.org/10.1029/93JE01802)
Schulz, M., J.B. Blake, S.M. Mazuk, A. Balogh, M.K. Dougherty, R.J.
Forsyth, E. Keppler, J.L. Phillips, and S.J. Bame, Energetic-
Particle, Plasma, and Magnetic-Field Signatures of a Poloidal
Pulsation in Jupiter's Magnetosphere, Planet. Space Sci., 41, 963,
1993.
(https://doi.org/10.1016/0032-0633(93)90101-7)
Tsurutani, B.T., C.M. Ho, R. Sakurai, B.E. Goldstein, A. Balogh, and
J.L. Phillips, Symmetry in discontinuity properties at the north and
south heliographic poles: Ulysses, Astron. Astrophys., 316, 342-345,
1996.
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