File: pvomgd.txt ----------------------------------------------------------------------- PVO INTERPLANETARY DATA PIONEER VENUS ORBITER (PVO) was the first orbiter mission designed to conduct a comprehensive and long term investigation of the planet Venus. PVO measured the detailed structure of the upper atmosphere and ionosphere of Venus and investigated the interaction of the solar wind magnetic field and plasma with the venusian ionosphere. Over the years 1978-1992 PVO provided nearly continuous measurements of the solar wind from its highly eccentric orbit around Venus. PI of magnetic field data: Dr. T. C. Russell, USLA. PI of plasma data: Dr. Aaron Barnes, Ames Research Center, NASA. plasma data were provided by Dr. P. Gazis, Ames,NASA. For the hourly resolution records, the PVO directory contains files with hourly averages for selected parameters of the interplanetary magnetic field (1978-12-05 - 1988-08-07) solar wind plasma (1978-12-05 - 1992-10-08) and the spacecraft trajectory (1978-12-05 - 1992-12-31) in RTN, and in Venus-centered (1978-12-05 - 1988-08-07) coordinates. These were data taken from time intervals when the spacecraft was outside the bow shock of the venusian ionosphere and in the solar wind. Time Coverage of merged files: 78-12-05 - 92-12-31. PVO data have been reprocessed to ensure a uniformity of content and coordinate systems relative to data from other deep-space missions: - All spacecraft trajectory data were transformed to a Heliographic Inertial (HGI) coordinate system. - calculation of RTN components of interplanetary magnetic field from VSO coordinates. - merging of trajectory coordinates, magnetic field data, and plasma data files into a single annual file PVO_YR.asc, where YR is the year; - Data gaps were filled with dummy numbers for the missing hours or entire days to make all files of equal length. The character '9' is used to fill all fields for missing data according to their format, e.g. ' 9999.9' for a field with the FORTRAN format F7.1. Note that format F7.1 below really means (1X,F6.1),etc. For the daily resolution data (one file), simple averages were taken over the hourly values. The format is identical to that for the hour averages However, the "hour" field has 0 as a value.and the "Magnitude of Average Vector" field is the simple average of the 24 hourly values of this parameter. Format Description: WORD ASCII MEANING UNITS/COMMENTS 1 I4 YEAR 1977,1978......... 2 I4 DECIMAL DAY January 1 =Day 1 3 I3 HOUR (0,1,......23) 4 F7.1 X VSO in radius of Venus (RV) 5 F7.1 Y VSO RV 6 F7.1 Z VSO RV 7 F7.2 Radial distance from Sun to Venus AU 8 F7.1 Heliographic Inertial latitude DEGREES, +,-90. of Venus 9 F7.1 Heliographic Inertial longitude DEGREES (0-360) of Venus 10 F7.2 Bx VSO NANOTESLAS 11 F7.2 By VSO NANOTESLAS 12 F7.2 Bz VSO NANOTESLAS 13 F7.2 BR RTN coordinate system NANOTESLAS 14 F7.2 BT RTN coordinate system NANOTESLAS 15 F7.2 BN RTN coordinate system NANOTESLAS 16 F7.2 Scalar B NANOTESLAS 17 F7.1 Proton flow speed, RTN km/s 18 F7.1 THETA-elevation angle degrees of flow velocity vector (RTN-cordinate system) 19 F7.1 PHI- azimuth angle of degrees flow velocity vector. (RTN-coordinate system) 20 F9.4 Proton density [n/cc] 21 F9.0 Proton Temperature degrees, K REFERENCES: 1. L. Colin and D.M. Hunten, Space Science Reviews 20,451,1977. DESCRIPTION OF COORDINATE SYSTEMS The Heliographic Inertial (HGI) coordinates are Sun-centered and inertially fixed with respect to an X-axis directed along the intersection line of the ecliptic and solar equatorial planes. The solar equator plane is inclined at 7.25 degrees from the ecliptic. This direction was towards ecliptic longitude of 74.36 degrees on 1 January 1900 at 1200 UT; because of precession of the celestial equator, this longitude increases by 1.4 degrees/century. The Z axis is directed perpendicular and northward from the solar equator, and the Y-axis completes the right-handed set. This system differs from the usual heliographic coordinates (e.g. Carrington longitudes) which are fixed in the frame of the rotating Sun. The RTN system is fixed at a spacecraft (or the planet). The R axis is directed radially away from the Sun, the T axis is the cross product of the solar rotation axis and the R axis, and the N axis is the cross product of R and T. At zero Heliographic Latitude when the spacecraft is in the solar equatorial plane the N and solar rotation axes are parallel. Venus Solar Orbital (VSO) coordinates are defined with respect to the orbital plane of Venus which is tilted about two degrees from the Ecliptic. The VSO system is Venus-centered with the X axis towards the Sun, the Z axis northward and perpendicular to the orbital plane, and the Y axis completing the right hand system. Acknowledgement: Hour averages of the interplanetary solar wind data from, and hourly heliocentric coordinates of, PVO and other interplanetary spacecraft may be also be accessed and plotted on-line through the COHOWeb service http://omniweb.sci.gsfc.nasa.gov/coho --------------------------------------------------------------