Ionopause Crossing Dataset Description FILE_NAME = IONOPAUS.TAB RECORD_TYPE = FIXED_LENGTH FILE_RECORDS = 642 DATA_SET_ID = PVO-V-OETP-5-IONOPAUSELOCATION-V1.0 SPACECRAFT_NAME = PIONEER VENUS ORBITER INSTRUMENT_NAME = ELECTRON TEMPERATURE PROBE TARGET_NAME = VENUS START_TIME = 1986-01-31T23:22:13.000Z STOP_TIME = 1992-10-07T19:46:27.000Z START_ORBIT_NUMBER = 2501 STOP_ORBIT_NUMBER = 5055 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). 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. DATA QUALITY/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. NOTE: The original submission by the P.I. was formatted for printing with header lines inserted every 50 orbits. PDS/PPI has removed these imbedded headers so that the file can be easily loaded into database or spreadsheet software. If a user would like a copy of this data file in its original format, the PPI Node of the PDS will provide a copy of that file electronically to the user. Please send e-mail to pds_operator@igpp.ucla.edu to request this data file. ----------------------------------------------------------------- Example data with header The "1" in column 1 indicates 8 lines of header are to follow. The only 1's in column 1 are these header block markers. ----------------------------------------------------------------- 1 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 00:00:00 0.0 0.0 0. 0.0 2 78340 14:21:42 49079 13:37:59 49.1 5.8 9899. 96.4 0 00:00:00 0.0 0.0 0. 0.0 3 78341 14:31:46 50202 13:56:42 56.3 6.3 7725. 91.3 0 00:00:00 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 REFERENCES Alexander, C. J., C. T. Russell, Solar cycle dependence of the location of the 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 configuration and evidence for ion escape, J. Geophys. Res., 92, 15, 1987. Brace, L. H., W. R. Hoegy, and R. F. Theis, Solar EUV measurements at Venus based on photoelectron emission from the Pioneer Venus Langmuir probe, J. Geophys. Res., 93, 7282, 1988. 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.