Pioneer Venus Orbiter OETP Data - 7/23/93
INTRODUCTION
This document describes the various Orbiter Electron Temperature Probe
(OETP) data products that have been submitted to the National Space
Science Data Center and the Planetary Data System.
The OETP has been described by Krehbiel et al. (1980). The instrument
uses two cylindrical Langmuir probes (axial and radial) which protrude
into the surrounding plasma to measure the ionospheric electron density
and temperature (Ne and Te), the ion density (Ni), and the spacecraft
potential, (Vs). The probes were operated independently by a common
electronics unit. All of the data submitted here were derived from the
radial probe, since its longer boom provided measurements over a wider
range of Ne, a fact that caused the investigators to dedicate the limited
telemetry allocation to that probe during most of the PVO mission. During
the first 70 orbits, the axial probe was used more often, so many of these
early orbits are not represented in the archived OETP data.
As an ionosphere instrument, the OETP is capable of accurate plasma
measurements only while the spacecraft was within the ionosphere; an
interval of only a few minutes during each 24 hour orbit. However, the Ne
measurements made at higher altitudes have proved useful, so they are
included in the High Resolution file which extend above the ionosphere.
These data are useful for the study of smaller scale features and for
identifying the location of the ionopause, the bow shock. The
measurements of photoelectron emission from the probe (net ion current
in regions of very low Ne) have permitted the intensity of the solar EUV
flux to be derived, and a file of daily values of this current is presented.
Details of the plasma measurements method can be found in the Krehbiel
et al. (1980) paper, and the method for solar EUV flux measurement is
described by Brace et al.(1988). The data formats for these files are
described at the end of this report. For further information on access to
the OETP raw telemetry data please contact Robert Theis or Walter Hoegy,
Code 914, NASA/Goddard Space Flight Center, Greenbelt, MD 20771. (301-
286-3620, and 301-286-3837).
The OETP measurements have been used in many Venus investigations.
Among these is a paper by Theis et al. (1984) who modelled the Ne and Te
data to describe the local time and altitude variations in the Venus
ionosphere and their implications for nightward ion flow. Brace et al.
(1987, 1990) used the OETP data to examine the nightside ionosphere out
to very high altitudes. A more complete bibliography publications by the
OETP investigators is given at the end of this document.
TYPES OF OETP DATA Products
Five types of OETP data files are available in the NSSDC and PDS. These are
described briefly in this section. More details on the measurements and
their accuracies are provided in later sections.
(1) The UADS. The Unified Abstract Data System, UADS, was conceived as
a file combine the data from all of the PVO in situ instruments on a
common time base to facilitate analysis. The temporal resolution of 12
seconds was adopted since it was approximately equal to the spin period
of the satellite which in most instruments determined the spatial
resolution of the measurements. data. The OETP input to the UADS
includes measurements of Ne, Te, and Vs, based on computer fitting of
individual voltampere curves. Since the curves were recovered at rates
either higher of lower than the UADS rate of 12 seconds, the value of the
parameter at the UADS entries had to be obtained by interpolation of
nearby measurements. When the spacecraft data rate was very low not all
UADS 12 second time slots were filled to avoid interpolation over too large
an interval.
UADS measurements are only provided when the spacecraft is in the
ionosphere and the density exceeds a threshold that depends on various
experimental background factors, such as spacecraft photoemission,
spacecraft charging, and electrical shielding of the probe by the spacecraft
ion sheath. For this reason, the UADs is not the best source of information
on the ionopause and its density gradients. These features are better
resolved in the High Resolution Ne file that is described next.
(2) The High Resolution Ne File. These data are based on measurements of
the electron saturation current or the ion saturation current taken from as
many voltampere curves as the telemetry data rate permitted. Since Ne is
assumed equal to Ni everywhere in the ionosphere, either can be used as a
measure of Ne. The ion current is used at high densities (Ni>4x10^4 cm^-3)
and the electron current is used at lower densities. Typically, 4 to 8 high
resolution density samples are obtained in the interval between recovered
voltampere curves, although this ratio is bit rate dependent. This provides
Ne and Ni measurements at much smaller intervals than is possible from
the voltampere curves themselves. High resolution measurements are
typically available at 2 to 8 second intervals depending upon the telemetry
rate available to the OETP at the time.
The measurements in the High Resolution Ne file are given for a one hour
period centered on periapsis, in spite of the fact that the spacecraft may
be outside the ionosphere for much of this interval. The measurements
made outside the ionosphere are heavily spin modulated by spacecraft
photoelectrons, but they are included because they show the ionopause
density gradient and other real Ne structure that lies above the ionosphere
(such as; bow shocks, plasma clouds, magnetosheath electron fluxes,
spacecraft photoelectron densities, etc). These features are not generally
found in the UADS file which only contains measurements made within the
ionosphere. More information on the High Resolution Ne measurements,
and their limitations is contained in the section on measurement accuracy.
(3) The Ionopause File. This file gives the orbit-by-orbit times and
locations of the ionopause crossings, which are evident as sharp gradients
in Ne at the top of the ionosphere. (These crossings always occur within 30
minutes of periapsis, so they may be seen in the High Resolution Ne files).
(4) The Bow Shock File. This file gives the orbit-by-orbit times and
locations of the bow shock crossings, which are characterized by distinct
changes in Ne. Multiple shock crossing are listed if they are sufficiently
separated to be resolved accurately. (Bow shock crossings will be evident
in the High Resolution Ne File when they occurred within 30 minutes of
periapsis).
(5) The Solar EUV Daily Values File. This file gives the magnitude of the
photoemission current from the radial probe, Ipe, (in units of 10^-9 amps).
Ipe dominates the ion current measurements outside the Venusian
ionosphere, making possible the serendipitous measurement of the total
solar EUV flux. The latter is an important parameter because solar EUV is
the main source of ionization and heating for the Venusian thermosphere
and ionosphere. The method is discussed by Brace et al., (1988).
The pe current measurements are taken just before PVO leaves the solar
wind and enters the magnetosheath (usually an hour or two before
periapsis). This approach provides the solar EUV flux that the Venus
thermosphere received just before the periapsis measurements. The
maximum value of the spin modulated Ipe is taken because it corresponds
to a probe orientation perpendicular to the Sun when the maximum area
of the probe is exposed to the Sun. Ipe is proportional to the intensity of
the ionizing component of solar radiation, so it is possible to derive the
total solar EUV (and far UV) flux. Ly alpha contributes approximately half
of the Ipe while nearly all of the rest is produced by radiation between 200
A and 1200 A which ionizes, excites and dissociates thermospheric
neutrals. The equation for conversion to solar EUV total flux is described
later.
Raw Data Tapes
The OETP raw telemetry data were provided by the PV Project on tapes
called Experiment Data Records (EDRs); one tape for each of the
approximately 5000 orbits. To conserve storage space, the EDRs were
compacted onto 6250 bpi magnetic tapes, each containing the data from
40 to 50 consecutive orbits. These compacted EDRs are now stored at
Goddard Space Flight Center, and the original EDRs were returned to NASA
for reuse. There is no current plan for submission of the 100 or so
compacted tapes to the NSSDC or the PDS for longer term storage, but they
are available if such a plan arises. There is a tentative plan to further
condense the raw OETP data onto optical disks for ease of storage and
permanence. (For further information on the current status of the raw
data, contact Walter R. Hoegy or Robert F. Theis, Code 910, NASA/GSFC,
Greenbelt, MD 20771, phone 301-286-3837 or 286-3620).
Voltampere Curves
Note that raw voltampere curves are not included in the NSSDC and PDS
data submissions; only the analyzed products of curve fitting. The curves
themselves can only be obtained by accessing the OETP compacted
magnetic tapes and applying appropriate computer codes that strip out the
curves from the OETP bit stream. These data products are not usually
archived by the data centers. This is unfortunate because we have found
the curves to be rather useful in unanticipated ways. For example, small
scale Ne structure has been discovered as wavelike modulation of the
voltampere curves (see reference 80 at end of report). Also, non-
maxwellian electron energy distributions are sometimes seen as
nonexponential electron retarding regions. (See Walter Hoegy or Robert
Theis at NASA/GSFC for information on the OETP raw data base and the
necessary programs to access the curves).
MORE DETAILED DESCRIPTION OF THE OETP DATA FILES
The UADS File
This file gives the Ne, Te and Vs measurements derived by fitting the radial
probe voltampere curves taken whenever PVO was within the ionosphere
(ie., between the inbound and outbound ionopause crossings). Data from
essentially every orbit in 1979 and 1980 included ionosphere transits.
After the summer of 1980, however, periapsis could no longer be
maintained at low altitudes, and it rose slowly. After April 1981 periapsis
was above the altitude of the dayside ionopause, so the spacecraft
encountered the ionosphere only in the terminator regions and on the
nightside where the ionosphere extends to much higher altitudes. Dayside
measurements again became available early in 1992 when periapsis
returned to low enough altitudes. The PVO Entry period of between July
and October 1992 provided only nightside periapsis data. During the
intervening period (1981-91), only nightside UADS measurements in the
high altitude (downstream) ionosphere were available. Note that High
Resolution Ne data from the 1981-91 interval provide measurements in the
dayside magnetosheath and in the solar wind, but these data have limited
accuracy because of spacecraft photoelectron contributions. See Brace et
al, 1988 (ref. 53) in the bibliography for further details on the
interpretation of High Resolution measurements made outside the
ionosphere.
As noted earlier, the geophysical values are listed at 12 second intervals in
the UADS. Each OETP entry represents a time-weighted average of those
radial probe measurements taken within approximately 10 seconds of the
UADS-assigned times. If no voltampere curves were recovered within that
20 second interval (this occurs at very low spacecraft telemetry rates), no
UADS value is entered in that 12 second slot. The instrument actually
takes voltampere curves at a rate of 120/minute, but telemetry rate
limitations permit the recovery of raw voltampere curves at intervals
between 4 to 32 seconds, depending upon the telemetry rate and
spacecraft data format currently in use.
The Ne values in the UADS file may actually be based on either the ion or
electron current collected by the probe, depending upon the magnitude of
the density at the time. The radial probe electron currents saturate the
electrometer when Ne > 4x10^4 cm^-3, so it is necessary to switch over to Ni
measurements at that point. Since the ion currents are about a factor of
50 smaller, the Ni measurements can be made up to densities of about 2 x
10^6 cm^-3, much greater than is present anywhere in the Venus ionosphere.
We assume that Ni = Ne everywhere in the ionosphere, so either may be
used to construct the UADS file. To minimize any discontinuity that may
occur at the Ne/Ni switch-over point due to systematic measurement
errors, Ne is normalized to Ni using a small universal correction factor.
This factor is 0.7, and is based on comparisons of the overlapping Ne and
Ni measurements from many individual orbits.
There are good theoretical reasons to believe that the Ni measurements
are inherently more accurate at densities exceeding 3 or 4x10^4 cm^-3, so
this normalization approach improves the accuracy of the Ne
measurements. The Ni measurements become less accurate at lower
densities because of uncertain changes in the ion composition, ion drift
velocity, and a positive ion current component produced by
photoelectrons (Ipe) leaving the probe. Ipe becomes comparable to the
true ion currents at Ni of approximately 1x10^4 cm^-3. The pe currents
produce a spin modulated signal that is modelled using measurements
made in the solar wind just prior to the bow shock crossing where the
ambient densities are too small to produce detectable ion currents. This
spin modulated Ipe waveform, whose amplitude is different from orbit to
orbit because of solar EUV variations, is subtracted from the net positive
current measurements made in the subsequent ionospheric passage. This
subtraction gives the true ion current which is directly convertible to Ni.
The spin maximum Ipe for each orbit is also used to construct the solar
EUV file, as is described later.
Because of the low spatial resolution of the UADS, and the fact that only
ionosphere data are included, this file is not the best source of
information about the ionopause. Features such as the ionopause, and
plasma clouds above the ionopause, are resolved better using the High
Resolution Data File which is not restricted to measurements within the
ionosphere. This file is discussed next.
High Resolution Ne File
The High Resolution file provides measurements of Ne (or Ni) within 30
minutes either side of periapsis at somewhat higher resolution than is
possible from the voltampere curves. However, these measurements are
less accurate when the spacecraft is outside the ionosphere, where Ne is
typically well below 100 cm^-3. In sunlight, spacecraft photoelectron
densities at the radial probe location are of the order of 30-50 cm^-3. In
darkness, the Ne measurements can be made down to densities of about 2
cm^-3 because the pe background is absent. However, the measurements
made in the Venus umbra are often degraded at low densities because of
the presence of hot electrons that charge the spacecraft to potentials that
lie beyond the range of the OETP sweep voltage. This makes it impossible
to drive the probe positive with respect to the plasma potential. In
addition, deBye shielding causes the probe to become enveloped in the ion
sheath of the spacecraft at very low densities, further reducing its access
to the ambient ionospheric plasma. Empirically derived corrections for
this effect have been applied to the high resolution data in order to
provide at least a lower limit of Ne, but the errors could exceed a factor of
2 at densities below 10 cm^-3. This correction does not allow Ne to be less
than 2 cm^-3. When the electron current at maximum positive voltage is
less than a certain very low value an Ne value of 2 cm^-3 is entered in the
High Resolution file simply to serve as an upper limit on Ne, and to show
that data were actually being taken.
In summary, the high resolution Ne measurements provide about a factor
of 8 higher resolution than the UADS file whose resolution is limited by
the recovery rate of raw voltampere curves. Therefore the high resolution
data better resolve such small scale features as the ionopause and the
plasma clouds often found above the ionopause. Also, the UADS densities
often stop somewhere within the ionopause density gradient, so this
feature can best be resolved using the High Resolution data. However,
certain artifacts have not been removed from the data, so one must be
careful not of over-interpret them. (See section on accuracy
Ionopause and Bow Shock Crossings
The ionopause and bow shock crossing times and locations are easily
identified in the high resolution Ne measurements (Theis et al., 1980).
These files contain the UT, altitude, latitude, SZA and local time of each
crossing.
On the dayside, the ionopause is taken (somewhat arbitrarily) at the level
in the steep gradient of the ionopause where Ne = 1x10^2 cm^-3. On the
nightside, the ionopause is selected at somewhat lower densities because
the absence of spacecraft photoelectrons lowers the Ne measurement
threshold. In both cases, the intent is to identify the ionopause as the
point where the first rise of Ne above the background density occurs. Of
course, the ionopause itself is not a point but is the extend region in which
the ionopause density gradient occurs.
The bow shock is a much more discrete feature in the data than the
ionopause. Multiple shock crossings sometimes occur because the shock
often moves at higher velocities than the satellite. In these cases, only the
outer most shock crossing is recorded, unless the separation between the
crossings is greater than a minute or two. The occurrence of multiple
shocks in the Bow Shock File provides a record of the orbits in which the
solar wind itself was probably highly variable. Because of the geometry of
the orbit, most shock crossings were in the range of 45 to 135o SZA.
However, the nose region of the shock was explored between 1985 and
1987 when PVO periapsis was near the equator and was at altitudes
between 2000 and 2300 km. During these years near solar minimum the
nose of the shock often moved down into that altitude range (Russell et al,
1988). During the subsolar passages of these years, the orbit
approximately paralleled the shock, sometimes inside, sometimes outside,
thus providing interesting snapshots of its movements.
Solar EUV Daily Values
This file contains the daily average value of the photoelectron emission
current, Ipe, from the radial probe, usually measured about 1 hr before
periapsis. The Ipe values are given in units of 10^-9 amperes. The data
cover the interval from 1979 through early 1992 when periapsis got low
enough to cause photoelectric yield changes that have not been fully
resolved and corrected for appropriately. The data provided cover orbits
1 to 4800. After orbit 4800, when PVO began to enter the atmosphere, the
Langmuir probe could no longer be kept clean, and as a result the yield changed
For further details, contact Walt Hoegy at GSFC code 914, (301) 286-3837 or
email hoegy@mite.gsfc.nasa.gov.
The daily Ipe measurements can be converted into the total solar EUV flux
(VEUV) using the following the equation given by Brace et al., (1988),
VEUV = 1.53 x 1011 Ipe (photons/cm2/s)
VEUV represents the total solar flux, weighted by the known wavelength-
dependent yield of the collector. A standard Hinteregger solar EUV/UV
spectrum is assumed to derive the coefficient, but the measurement is
relatively insensitive to this assumption over the typical range of variations
in the solar spectrum.
The VEUV data have been useful in the study of solar EUV effects on the ion
production and electron heating rates in the Venus ionosphere. VEUV
variations have been correlated with changes in the density and
temperature of the ionosphere (Elphic et al., 1984), the height of the bow
shock (Alexander et al., 1985, Russell et al., 1988), and changes in the
density and temperature of the thermosphere (Mahajan et al., 1990).
DATA QUALITY/ACCURACY
UADS Accuracy
The UADS data are based on operator-assisted voltampere curve fits. The
absolute accuracy of the data depends primarily upon the accuracy of the
Langmuir probe theory (Krehbiel, et al., 1980) and our success in avoiding
the inclusion of data from curves that were obtained in situations in which
the theory does not apply (e.g., probe in wake of the telemetry antenna,
very low densities, pe contamination, spacecraft potential too negative,
etc.). Where these effects have been avoided, the errors in Te should not
exceed 5% when Ne exceeds 500 cm^-3 in sunlight and about 30 cm^-3 in
darkness. However, Te errors may be larger in regions of great spatial
structure where the plasma parameters change while they are being
measured, or in regions where the electron energy distribution is
nonmaxwellian or appears to have two temperatures. These conditions are
often found in the nightside ionosphere and at the ionopause. In these
cases, the curve-fitting is done so as to measure the temperature of the
lower temperature component of the plasma. The curves would have to be
refitted to obtain information on the higher temperature component.
The accuracy of the Ne measurements is determined by the accuracy of the
Ni measurements to which they are normalized by a fixed factor that was
determined by comparisons at densities in the vicinity of 4 x 10^4 cm^-3.
Therefore the Ne accuracy is nominally 10%, but the error increases at low
densities where pe background and/or spacecraft charging effects can be
important, as described earlier. Ne is given in the UADS file for densities
down to 2 cm^-3 and Te for densities down to 10 cm^-3, which are observed
only in the nightside ionosphere and ionotail. The Ne error is expected to
grow as the density approaches these limits, but the Te measurements are
less subject to error at low densities because knowledge of Vs is not
needed to obtain the temperature. In spite of the reduced accuracy, Ne
measurements below 30 cm^-3 are retained in the UADS file because they
do reflect real variations that may be of interest even when their absolute
accuracy may be uncertain by a factor of 2 or more. Examples include the
detection of weak ionospheric tail rays and plasma clouds (Brace et al.,
1987).
The error in Ni is not expected to exceed 10% at densities above 4 x10^4
cm^-3. Ne is used for densities below 4 x10^4 cm^-3. As noted earlier, Ne is
normalized to Ni at their overlap point to gain the greater inherent
accuracy of the ion measurements. The normalization factor is based on
the overlapping Ne and Ni measurements from many orbits, and the factor
does not change throughout the mission. Therefore, small discontinuities
in the density measurement may sometimes be seen at the crossover point
if ionospheric conditions lead to unusual spacecraft potentials, ion
compositions, or other factors that are assumed constant when adopting a
fixed relationship between the ion and electron currents. We assume that
the normalization factor remains constant over the full range of Ne, and
this may not be correct.
High Resolution File Accuracy
In general, the high resolution Ne measurements have a lower absolute
accuracy than the UADS (voltampere curve) measurements because
factors such as the spacecraft potential and Te are not available to
calculate Ne more precisely. To reduce such errors in the high resolution
data, they are normalized to the voltampere curve measurements. This
normalization is entirely different from the Ne-Ni normalization employed
in deriving the UADS data.
Another source of error in the High Resolution Ne measurements is the
jump discontinuities that occur when the spacecraft passes from sunlight
to shadow. An abrupt change in spacecraft potential occurs at that point,
and this changes the probe voltage which is referenced to the spacecraft.
The Ne measurements cannot easily be corrected for this change because
they are not based on voltampere curves but measurements at a fixed
positive potential. Therefore a discontinuity may occur in Ne at the
sunlight-shadow boundary if Ne is sufficiently low that spacecraft
photoelectron emission affects the spacecraft potential.
The precision of the high resolution data is probably somewhat better than
that of the UADS data because the latter may suffer from the effects of
volt ampere curve distortion due to small scale density variations and spin
effects which do not show up in the single point samples used in the high
resolution measurements. This feature makes the high resolution data
more valuable in resolving small scale, and small amplitude plasma
structure.
Ionopause Location Accuracy
The ionopause location is selected at that point in the steep gradient of the
ionopause where Ne crosses through the level of 1x10^2 cm^-3. When the
spacecraft is in darkness, the pe background is absent and the ionospheric
Ne is also much lower, so the ionopause is identified as the first rise in Ne
above whatever background is present. The ionopause is identified by a
human operator who views each high resolution Ne pass plot on an
interactive computer terminal. He selects the ionopause somewhat
subjectively as the time of the first rise above the background Ne, which
may consist of magnetosheath plasma or photoelectrons. The 40 minute
pass plots used for this purpose provide only a 5-10 second accuracy in
the crossing times. When irregularities or waviness in the ionopause
produce several ionopause crossings, the outer most crossing is the only
one identified.
Bow Shock Location Accuracy
The bow shock is selected from 200 minute pass plots by marking the UT
of the sharp change in the amplitude of Ne at the shock discontinuity. The
resolution of the shock crossing time is of the order of 1 minute on these
plots, but this could be improved to a few seconds if expanded plots were
used. There is no plan currently to provide the ultimate resolution
available in bow shock crossing time and location.
The solar EUV measurement accuracy
The Ipe measurements themselves are made with an absolute accuracy of 1
to 2%, depending upon where the current falls within the decade range of
the ranging electrometer. The absolute accuracy of the measurements is
also limited by our knowledge of the photoelectric yield of the radial
probe collector, and our assumption that a Hinteregger standard EUV/UV
spectrum is correct. We estimate a 10% absolute accuracy in the total EUV
flux and a 1 to 2% relative accuracy or precision provided by the accuracy
of the current measurements themselves. See Brace et al.(1988) for
details of the method.
FORMAT OF THE FILES
The following is a guide to reading the data in the Pioneer Venus
Unified Abstract Data System tape format. The first record gives the
number of parameters, followed by the 4 letter mnemonic that
identifies the parameter. The parameters given are ELTE (Te in units of
Deg. K), ELNE, (Ne in number/cc), and VS (Vs in volts) in following
format
3 ELTE ELNE VS
The second record contains the format which may be used to read all
of the remaining records.
(I8,I9,I5,I6,3F11.2)
The third record contains values which are used to indicate that no
measurement was available.
0 0 0 0 9999999.00 9999999.00 9999999.00
The fourth record to the end of the file, consists of the date (year and
day of year), the UT (milliseconds), the orbit number and the time
from periapsis (in seconds). The last three columns are Te, Ne, and Vs.
1978339 54454817 1 -228 9999999.00 574.00 -2.10
1978339 54550817 1 -132 5470.00 12900.00 -0.42
1978339 54682817 1 12 3960.00 11800.00 -0.57
1978339 54814817 1 144 6900.00 1090.00 0.38
1978340 51262817 2 -444 9999999.00 243.00 2.84
1978340 51322817 2 -384 8760.00 55800.00 -1.75
The next file contains ionopause crossing information. This file is
formatted for printing and is self explanatory.
ORBIT DATE PERIAPSIS INBOUND CROSSING OUTBOUND CROSSING
HH:MM:SS SECS HH:MM:SS LAT LST ALT SZA SECS HH:MM:SS LAT LST ALT SZA
1 78339 15:11:12 54409 15: 6:49 39.7 15.6 601. 63.4 54884 15:14:44 1.5 16.4 522. 66.2
2 78340 14:21:42 51276 14:14:36 52.1 15.2 832. 66.4 52130 14:28:50 -15.8 16.8 834. 72.9
3 78341 14:31:46 51971 14:26:11 45.9 15.6 579. 66.2 52690 14:38:10 -13.0 16.9 687. 73.7
4 78342 14:40:12 52272 14:31:12 59.6 14.9 1110. 69.5 53271 14:47:51 -18.7 17.1 867. 77.1
The next file contains bowshock crossing information. This file is
formatted for printing and is self explanatory.
ORBIT DATE PERIAPSIS INBOUND CROSSING OUTBOUND CROSSING
HH:MM:SS SECS HH:MM:SS LAT LST ALT SZA SECS HH:MM:SS LAT LST ALT SZA
1 78339 15:11:12 51512 14:18:32 43.9 5.4 12044. 100.2 0 0: 0: 0 0.0 0.0 0. 0.0
2 78340 14:21:42 49079 13:37:59 49.1 5.8 9899. 96.4 0 0: 0: 0 0.0 0.0 0. 0.0
3 78341 14:31:46 50202 13:56:42 56.3 6.3 7725. 91.3 0 0: 0: 0 0.0 0.0 0. 0.0
4 78342 14:40:12 49872 13:51:12 45.1 5.8 11284. 96.2 57078 15:51:18 -67.8 2.0 16416. 109.1
The next file contains Venus Solar Flux information in the form of Ipe
values in units of 10^-9 amperes. This file is formatted for printing and
is self explanatory. The total solar EUV flux (VEUV)is derived by
multiplying by the factor given in the equation presented earlier.
Dates 78339-78348 Orbits 1- 10 ipe 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Dates 78349-78358 Orbits 11- 20 ipe 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Dates 78359-79003 Orbits 21- 30 ipe 0.00 0.00 0.00 0.00 10.30 0.00 0.00 0.00 0.00 10.30
Dates 79004-79013 Orbits 31- 40 ipe 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Dates 79014-79023 Orbits 41- 50 ipe 0.00 10.30 0.00 0.00 0.00 10.30 10.02 10.02 0.00 10.02
Dates 79024-79033 Orbits 51- 60 ipe 0.00 0.00 10.02 10.11 0.00 0.00 0.00 0.00 0.00 0.00
Dates 79034-79043 Orbits 61- 70 ipe 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10.98 11.19
Dates 79044-79053 Orbits 71- 80 ipe 11.03 11.19 10.34 9.74 10.39 11.40 11.61 0.00 11.40 10.78
Dates 79054-79063 Orbits 81- 90 ipe 9.52 0.00 9.70 10.11 9.97 0.00 9.97 9.65 0.00 9.52
Dates 79064-79073 Orbits 91- 100 ipe 9.70 10.39 10.54 10.59 10.78 10.83 10.98 10.88 10.83 0.00
REFERENCES
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Venus bow shock, Geophys. Res. Lett., 12, 369, 1985.
Brace, L. H., W. T. Kasprzak, H. A. Taylor, Jr., R. F. Theis, C. T. Russell,
A. Barnes, J. D. Mihalov, and D. M. Hunten, The ionotail of Venus: Its
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based on photoelectron emission from the Pioneer Venus Langmuir probe,
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Brace, L. H., W. T. Kasprzak, H. A. Taylor, R. F. Theis, C. T. Russell,
A. Barnes, J. D. Mihalov and D. M. Hunten, "The Ionotail of Venus: Its
Configuration and Evidence for Ion Escape," J. Geophys. Res., 92, 15, 1987.
Brace, L. H., R. F. Theis, and J. D. Mihalov, The Response of the Venus
Nightside Ionosphere and Ionotail to Solar EUV and Solar Wind Dynamic
Pressure,J. Geophys. Res., 95, 4075, 1990.
Elphic, R.C., L. H. Brace, R. F. Theis, and C. T. Russell, Venus Dayside
Ionosphere Conditions: Effects of magnetic field and solar EUV flux, Geophys.
Res. Lett., 11, 124, 1984.
Krehbiel, J. P., L. H. Brace, J. R. Cutler, W. H. Pinkus, and R. B. Kaplan,
Pioneer Venus Orbiter Electron Temperature Probe, IEEE Transactions on
Geoscience and Remote Sensing, GE-18, 49, 1980.
Mahajan, K. K, W. T. Kasprzak, L. H. Brace, H. B. Niemann, and W. R. Hoegy,
Response of the Venus Exospheric Temperature Measured by Neutral Mass
Spectrometer to the Solar EUV Measured by Langmuir Probe on the Pioneer
Venus Orbiter, J. Geophys. Res., 95, 1091, 1990.
Russell, C. T., E. Chou, J. G. Luhmann, P. Gazis, L. H. Brace, and W. R. Hoegy,
Solar and interplanetary control of the location of the Venus bow shock, J.
Geophysic. Res., 93, 5461, 1988.
Theis, R. F., L. H. Brace, K. H. Schatten, C. T. Russell, J. A. Slavin, J. A.
Wolf, The Venus ionosphere as an obstacle to the solar wind, Advances in Space
Research, 1, 47, 1980.
Theis, R. F., L. H. Brace, R. C. Elphic, and H. G. Mayr, New empirical models
of the electron temperature and density of the Venus ionosphere, with
applications to transterminator flow, J. Geophys. Res., 89, 1477, 1984.
BIBLIOGRAPHY OF OETP-RELATED PUBLICATIONS (as of July. 1993)
1. "Electron Temperatures and Densities in the Venus Ionosphere: Pioneer
Venus Orbiter Electron Temperature Probe Results," L. H. Brace, R. F. Theis, A.
F. Nagy, T. M. Donahue, M. B. McElroy, Science, 203, 763, 1979.
2. "On the Configuration of the Nightside Venus Ionopause," L. H. Brace, H.
A. Taylor, Jr., P. A. Cloutier, R. E. Daniell and A. F. Nagy, Geophys. Res.
Lett., 6, 345, 1979.
3. "An Empirical Model of the Electron Temperature and Density in the
Nightside Venus Ionosphere," L. H. Brace, R. F. Theis, H. B. Niemann, W. R.
Hoegy, and H. G. Mayr, Science, 205, 102, 1979.
4. "Comparison of Calculated and Measured Ion Densities on the Dayside of
Venus," A. F. Nagy, T. E. Cravens, R. H. Clien, H. A. Taylor, Jr., L. H. Brace
and H. C. Brinton, Science, 205, 107, 1979.
5. "Absorption of Whistler Mode Waves in the Ionosphere of Venus," W.W.L.
Taylor, F. L. Scarf, C. T. Russell, L. H. Brace, Science, 205, 112, 1979.
6. "Plasma Diffusion Into the Wake of Venus," T. Gombosi, T. E. Cravens,
A. F. Nagy, L. H. Brace and H. J. Owens, Geophys. Res. Lett., 6, 349, 1979.
7. "The Energetics of the Ionosphere of Venus: A Preliminary Model Based on
Pioneer Venus Observations," T. E. Cravens, A. F. Nagy, L. H. Brace,
R. H. Clien, and W. C. Knudsen, Geophys. Res. Lett., 6, 341, 1979.
8. "Evidence for Lightning on Venus," W. W. L. Taylor, F. L. Scarf,
C. T. Russell and L. H. Brace, Nature, 282, 614, 1979.
9. "Pioneer Venus Orbiter Electron Temperature Probe," J. P. Krehbiel,
L. H. Brace, J. R. Cutler, W. H. Pinkus, R. B. Kaplan, IEEE Transactions on
Geoscience and Remote Sensing, GE-18, 49, 1980.
10. "The Dynamic Behavior of the Venus Ionosphere," L. H. Brace, R. F. Theis,
W. R. Hoegy, J. H. Wolfe, C. T. Russell, R. C. Elphic, A. F. Nagy, J. Geophys.
Res., 85, 7663, 1980.
11. "Empirical Models of the Electron Temperature of the Venus Ionosphere,"
R. F. Theis, L. H. Brace, and H. G. Mayr, J. Geophys. Res., 85, 7787, 1980.
12. "Electron Temperature and Heat Flow in the Nightside Venusian Ionosphere,"
W. R. Hoegy, L. H. Brace, R. F. Theis, and H. G. Mayr, J. Geophys. Res., 85,
7811, 1980.
13. "Lightning on Venus: Orbiter Detection of Whistler Signals," F. L. Scarf,
W.W.L. Taylor, C. T. Russell and L. H. Brace, J. Geophys. Res., 85, 8158, 1980.
14. "Model Calculations of the Dayside Ionosphere of Venus: Energetics,"
T. E. Cravens, T. I. Gombosi, J. Kozyra, A. F. Nagy, and L. H. Brace, J.
Geophys. Res., 85, 7778, 1980.
15. "The Location of the Dayside Ionopause of Venus: Pioneer Venus Orbiter,"
R. C. Elphic, C. T. Russell, J. A. Slavin, L. H. Brace, A. F. Nagy, Geophys.
Res. Lett., 7, 561, 1980.
16. "The Solar Wind Interaction with Venus: Pioneer Venus Observations of Bow
Shock Location and Structure," J. A. Slavin, R. C. Elphic, C. T. Russell,
L. H. Brace, J. Geophys. Res., 85, 7625, 1980.
17. "Observations of the Dayside Ionopause and Ionosphere of Venus,"
R. C. Elphic, C. T. Russell, J. A. Slavin and L. H. Brace, J. Geophys. Res.,
85, 7679, 1980.
18. "The Venus Ionosphere as an Obstacle to the Solar Wind," R. F. Theis,
L. H. Brace, K. H. Schatten, C. T. Russell, J. A. Slavin, J. A. Wolfe, Advances
in Space Research, 1, 47, 1980.
19. "On the Formation of the Nightside Ionospheric Bulge in the Venus Wake,"
H. Perez-de-Tejada and L. H. Brace, Geofisica Internacional, 19, 213, 1980.
20. "The Dynamical Response of the Dayside Ionosphere of Venus to the Solar
Wind," R. E. Hartle, H. A. Taylor, Jr., S. J. Bauer, L. H. Brace, C. T.
Russell and R. E. Daniell, Jr., J. Geophys. Res., 85, 7739, 1980.
21. "On the Role of the Magnetic Field in the Solar Wind Interaction with
Venus: Expectations versus Observations," J. G. Luhmann, R. C. Elphic,
C. T. Russell and L. Brace, Adv. Space Res., 1, 123, 1981.
22. "Magnetic Flux Ropes in the Venus Ionosphere: In situ Observations of
Force-free Structures," R. C. Elphic, C. T. Russell, J. G. Luhmann and
L. H. Brace, Adv. Space Res., 1, 53, 1981.
23. "Large Scale Current Systems in the Venus Dayside Ionosphere",
J. G. Luhmann, R.C. Elphic, and L. H. Brace,J. Geophys. Res., 86, 3509, 1981.
24. "The Venus Ionopause Current Sheet: Thickness Length Scale and
Controlling Factors," R. C. Elphic, C. T. Russell, J. G. Luhmann, F. L. Scarf
and L. H. Brace, J. Geophys. Res., 86, 11430, 1981.
25. "Plasma Clouds above the Ionopause of Venus and Their Implications,"
L. H. Brace, R. F. Theis and W. R. Hoegy, Planet. Space Sci., 30, 29, 1982.
26. "Holes in the Nightside Ionosphere of Venus," L. H. Brace, R. F. Theis,
H. G. Mayr, S. A. Curtis and J. G. Luhmann, J. Geophys. Res., 87, 199, 1982.
27. "Magnetic Field and Plasma Wave Observations in a Plasma Cloud at Venus,"
C. T. Russell, J. G. Luhmann, R. C. Elphic, F. L. Scarf and L. H. Brace,
Geophys. Res. Lett., 9, 45, 1982.
28. "Pioneer Venus Observations of Plasma and Field Structures in the Near
Wake of Venus," J. G. Luhmann, C. T. Russell, L. H. Brace, H. A. Taylor, W. C.
Knudsen, F. L. Scarf, D. S. Colburn and A. Barnes, J. Geophys. Res., 87, 9205,
1982.
29. "Disappearing Ionospheres on the Nightside of Venus," T. E. Cravens,
L. H. Brace, H. A. Taylor, C. T. Russell, W. C. Knudsen, K. L. Miller,
A. Barnes, J. D. Mihalov, F. L. Scarf, S. J. Quenon and A. F. Nagy, ICARUS, 51,
271, 1982.
30. "Observations of Energetic Ions Near the Venus Ionopause," W. T. Kasprzak,
H. A. Taylor, L. H. Brace, H. B. Niemann, F. L. Scarf, Planet. Space Sci., 30,
1107, 1982.
31. "Structure and Dynamics of the Ionosphere," A. F. Nagy and L. H. Brace,
Nature, 296, 19, 1982.
32. "Observed Composition of the Ionosphere of Venus: Implications for the
Ionization Peak and the Maintenance of the Nightside Ionosphere,"
H. A. Taylor, Jr., R. E. Hartle, H. B. Niemann, L. H. Brace, R. E. Daniell, Jr.,
S. J. Bauer and A. J. Kliore, ICARUS, 51, 283, 1982.
33. "The Ionosphere of Venus: Observations and Their Interpretation," L. H.
Brace, T. I. Gombosi, A. J. Kliore, Wm. C. Knudsen, A. F. Nagy,
H. A. Taylor, Jr., Venus, Chapter 23, ed. D. Hunten, University of Arizona
Press, 1983.
34. "Wave Structure in the Venus Ionosphere Downstream of the Terminator,"
L. H. Brace, R. C. Elphic, S. A. Curtis, C. T. Russell, Geophys. Res. Lett.,
10, 1116, 1983.
35. "Plasma Distribution and Magnetic Field Orientation in the Venus Near
Wake: Solar Wind Control of the Nightside Ionopause," H. Perez-de-Tejada,
M. Dryer, D. S. Intrilligator, C. T. Russell and L. H. Brace, J. Geophys. Res.,
88, 9019, 1983.
36. "Effects of Large-Scale Magnetic Fields in the Venus Ionosphere",
J. G. Luhmann, R. C. Elphic, C. T. Russell, L. H. Brace, R. E. Hartle,
Adv. Space Res., 2, 17, 1983.
37. "Impact Ionization Effects on Pioneer Venus Orbiter," E. C. Whipple,
L. H. Brace and L. W. Parker, Proceedings of the 17th ESLAB Symposium on
Spacecraft Interactions, p. 127, ESA Report SP-198, 13-16 September 1983.
38. "New Empirical Models of the Electron Temperature and Density of the Venus
Ionosphere with Applications to Transterminator Flow," R. F. Theis, L. H. Brace,
R. C. Elphic and H. G. Mayr, J. Geophys. Res., 89, 1477, 1984.
39. "Venus Dayside Ionospheric Conditions: Effects of Magnetic Field and Solar
EUV Flux," R. C. Elphic, L. H. Brace, R. F. Theis and C. T. Russell, Geophys.
Res. Lett., 11, 124, 1984.
40. "Nightward Ion Flow in the Venus Ionosphere: Implications of Momentum
Balance," R. C. Elphic, H. G. Mayr, R. F. Theis, L. H. Brace, K. L. Miller and
W. C. Knudsen, Geophys. Res. Lett., 11, 1007, 1984.
41. "Pioneer Venus: Evolving Coverage of the Near-Venus Environment," L. H.
Brace and L. Colin, EOS, 65, 401, 1984.
42. "Current-Driven Instabilities and Auroral-type Particle Acceleration at
Venus," F. L. Scarf, S. Neumann, L. H. Brace, C. T. Russell, J. G. Luhmann, and
A. I. F. Stewart, Adv. in Space Res., 5, 185, 1985.
43. "Electron Densities and Temperatures in the Venus Ionosphere: Effects of
Solar EUV, Solar Wind Pressure and Magnetic Field," R. C. Elphic, L. H. Brace
and C. T. Russell, Adv. Space Res., 5, 313, 1985.
44. "CO2 Impact Ionization Driven Plasma Instability Observed by Pioneer Venus
Orbiter at Periapsis," S. A. Curtis, L. H. Brace, H. B. Niemann, and
F. L. Scarf, J. Geophys. Res., 90, 6631, 1985.
45. "The Venus Ionosphere," S. J. Bauer, L. H. Brace, H. A. Taylor,
T. K. Breus, A. J. Kliore, W. C. Knudsen, A. F. Nagy, C. T. Russell, and
N. A. Savich, Adv. Space Research, 5, 233, 1985.
46. "The Ionotail of Venus: Its Configuration and Evidence for Ion Escape,"
L. H. Brace, W. T. Kasprzak, H. A. Taylor, R. F. Theis, C. T. Russell,
A. Barnes, J. D. Mihalov and D. M. Hunten, J. Geophys. Res., 92, 15, 1987.
47. "Characteristics of the Marslike Limit of the Venus-Solar Wind
Interaction," J. G. Luhmann, C. T. Russell, F. L. Scarf, L. H. Brace, and
W. C. Knudsen, J. Geophys. Res., 92, 8545, 1987.
48. "Waves on the Subsolar Ionopause of Venus," C. T. Russell, R. N. Singh,
J. G. Luhmann, R. C. Elphic and L. H. Brace, Adv. Space Res., 7, (12)115, 1987.
49. "Asymmetries in the Location of the Venus Ionopause," J. L. Phillips,
J. G. Luhmann, W. C. Knudsen, and L. H. Brace, J. Geophys. Res., 93, 3927, 1988.
50. "Solar EUV Measurements at Venus Based on Photoelectron Emission from the
Pioneer Venus Langmuir Probe," L. H. Brace, W. R. Hoegy, R. F. Theis,
J. Geophys. Res., 93, 7282, 1988.
51. "Solar and Interplanetary Control of the Location of the Venus Bow Shock,"
C. T. Russell, E. Chou, J. G. Luhmann, P. Gazis, L. H. Brace and W. R. Hoegy,
J. Geophys. Res., 93, 5461, 1988.
52. "Periodic Solar EUV Flux Monitored Near Venus," Solar Physics, 123, 7,
1989.
53. "A Precursor to the Venus Bow Shock," L. H. Brace, R. F. Theis,
S. A. Curtis and L. W. Parker, J. Geophys. Res., 93, 12735, l988.
54. "On the Lower Altitude Limit of Venusian Ionopause," K. K. Mahajan,
H. G. Mayr, and L. H. Brace, Geophys. Res. Lett., 16, 759, 1989.
55. "Solar Wind Interactions with the Ionosphere of Venus Inferred from Radio
Scintillation Measurements," R. Woo, W. L. Sjogren, J. G. Luhmann, A. J. Kliore,
C. T. Russell, L. H. Brace, J. Geophys. Res, 94, 1473, 1989.
56. "A seven-month Cycle Observed with the Langmuir Probe on Pioneer Venus
Orbiter," J. Geophys. Res., 94, 8663-1989.
57. "Small Scale Plasma, Magnetic Field and Neutral Density Fluctuations in
the Nightside Venus Ionosphere," W. R. Hoegy, L. H. Brace, W. T. Kasprzak,
C. T. Russell, J. Geophys. Res., 95, 4085, 1990.
58. "The Response of the Venus Nightside Ionosphere and Ionotail to Solar
EUV and Solar Wind Dynamic Pressure," L. H. Brace, R. F. Theis, and
J. D. Mihalov,J. Geophys. Res., 95, 4075, 1990.
59. "Remote Sensing of Mars' Ionosphere and Solar Wind Interactions: Lessons
from Venus," J. G. Luhmann, A. J. Kliore, A. Barnes, and L. H. Brace, Adv.
Space Res., 10, 43, 1990.
60. "Response of Venus Exospheric Temperature Measured by Neutral Mass
Spectrometer to Solar EUV Measured by Langmuir Probe on the Pioneer Venus
Orbiter," K. K. Mahajan, W. T. Kasprzak, L. H. Brace, H. B. Niemann,
W. R. Hoegy, J. Geophys. Res., 95, 1091, 1990.
61. "Venus Bow Shock Precursor," E. G. Fontheim and L. H. Brace,
Adv. Space Res., 10, (5)11, 1990.
62. "Solar Cycle Variations in the Neutral Exosphere Inferred from the
Location of the Venus Bow Shock," C. T. Russell, E. Chou, J. G. Luhmann, and
L. H. Brace, Adv. Space Res., 10, 5, 1990.
63. "The Structure of the Venus Ionosphere," L. H. Brace and A. J. Kliore,
Space Sci. Rev., 55, 81-163, 1991.
64. "Solar EUV Index for Aeronomical Studies at Earth from Langmuir Probe
Photoelectron Measurements on the Pioneer Venus Orbiter," J. Geophys. Res., 97,
10525, 1991.
65. "Superthermal >36 eV Ions Observed in the Near Tail Region of Venus by the
Pioneer Venus Orbiter Neutral Mass Spectrometer," W. T. Kasprzak, J. M
Grebowsky, H. B. Niemann, and L. H. Brace, J. Geophys. Res., 96, 11175, 1991.
66. "Evidence for Unusually High Densities of Plasma in the Venusian
Ionosheath," D. S. Intrilligator, L. Brace, S. H. Brecht, W. Knudsen,
F. L. Scarf, and H. A. Taylor, Geophys. Res. Letts, 18, 61, 1991.
67. "Venus Ionospheric Tail Rays: Spatial Distributions and IMF Control,"
M. Ong, J. G. Luhmann, C.T. Russell, R.J. Strangeway, and L. H. Brace,
J. Geophys. Res., 96, 17751, 1991.
68. "Comparison of Observed Plasma and Magnetic Field Structures in the Wakes of
Mars and Venus," E. Dubinin, R. Lundin, W. Reidler, K. Schwingenschuh, J. G.
Luhmann, C. T. Russell, and L. H. Brace, J. Geophys. Res., 96, 11189, 1991.
69. "Near Mars Space," J. G. Luhmann and L. H. Brace, Rev. Geophys., 29, 121,
1991.
70. "Venus Ionospheric 'Clouds': Relationship to the Magnetosheath Field
Geometry," M. Ong, J. G. Luhmann, C. T. Russell, R. J. Strangeway and L. H. Brace, J. Geophys.
Res., 96, 11133, 1991.
71. "Small-Scale Plasma Irregularities in the Nightside Venus Ionosphere," J. M
Grebowsky, S.A. Curtis, and L. H. Brace, J. Geophys. Res., 96, 21347, 1991.
72. "Small-scale Density Irregularities in the Nightside Venus Ionosphere:
Comparison of Theory and Observations," J. D. Huba, and J. M Grebowsky,
J. Geophys. Res., in press 1992.
73 "The Intrinsic Magnetic Field and Solar Wind Interactions of Mars," J. G. Luhmann,
C. T. Russell, L. H. Brace, O. L. Vaisberg, pp 1090-1134, Mars, University of
Arizona Press, 1992.
74. "Effects of Solar EUV Variation on the Nightside Ionosphere of Venus
Observed on Langmuir Probe at Solar Maximum," S. Ghosh, K.K. Mahajan,
L. H. Brace, submitted J. Geophys Res, June 1992.
75. "A Reconsideration of the Effects of Terminator Ionopause Height on the
Nightward Ion Transport at Venus,", J. Kar, K. K. Mahajan, S. Ghosh, and
L. H. Brace, J. Geophys. Res, 97, A9, 13889, 1992.
76. "First Analyses of Recent PVO Plasma Analyzer Observations in the Venus
Ionotail at Altitudes ~1100 km: Evidence for Ion Acceleration"
D. S. Intrilligator, L. H. Brace, P. A. Cloutier, W. T. Kasprzak, W. C. Knudsen,
and R. J. Strangeway, submitted to G.R.L, 1993.
77 "Energetics of the Dayside Venus Ionosphere" A. F. Nagy, Zoltan Dobe,
L. H. Brace, T. E. Cravens, and J. G. Luhmann, (submitted GRL, 1993).
78 "The Magnetic State of the Lower Ionosphere During Pioneer Venus Entry
Phase", C. T. Russell, R. J. Strangeway, J. G. Luhmann, and L. H. Brace,
(submitted GRL, 1993).
79 "Ion Measurements During Pioneer Venus Reentry: Implications for Solar
Cycle Variation of Ion Composition and Dynamics, J. Grebowsky, R. E. Hartle,
J. Kar, P. A. Cloutier, H. A. Taylor, L. H. Brace,
(submitted to PVO entry issue of GRL, 1993).
80 "Kilometer-Sized Waves in the Electron Density in the Venusian Nightside
Ionosphere", L. H. Brace,( submitted to PVO entry issue of GRL, 1993).
81 "Solar Cycle Variations of Electron Density and Temperature in the
Venusian Nightside Ionosphere", Robert F. Theis, and Larry H. Brace,
(submitted to PVO entry issue of GRL, 1993).
82 "Plasma Waves Observed at Low Altitudes in the Tenuous Nightside
Ionosphere", R. J. Strangeway, C. T. Russell. C. M. Ho, and L. H. Brace,
(submitted to PVO entry issue of GRL, 1993).