NSSDCA ID: PSFP-00475
Availability: Archived at NSSDC, accessible from elsewhere
Time span: 1978-12-05 to 1992-01-18
This description was generated automatically using input from the Planetary Data System.
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. 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 wavelengthdependent 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). OBJECT = DSPARMINFO SAMPLING_PARAMETER_NAME = N/A SAMPLING_PARAMETER_RESOLUTION = N/A MINIMUM_SAMPLING_PARAMETER = N/A MAXIMUM_SAMPLING_PARAMETER = N/A SAMPLING_PARAMETER_INTERVAL = N/A MINIMUM_AVAILABLE_SAMPLING_INT = N/A SAMPLING_PARAMETER_UNIT = N/A DATA_SET_PARAMETER_NAME = PHOTOELECTRON CURRENT NOISE_LEVEL = UNK DATA_SET_PARAMETER_UNIT = AMPERES / 10**9 END_OBJECT = DSPARMINFO
These data are available on-line from the Planetary Data System (PDS) at:
https://pds-ppi.igpp.ucla.edu/data/PVO-V-OETP-5-SOLAREUV-24HRAVG-V1.0/
Questions and comments about this data collection can be directed to: Dr. David R. Williams
Name | Role | Original Affiliation | |
---|---|---|---|
Mr. Larry H. Brace | Data Provider | NASA Goddard Space Flight Center | |
Mr. Robert F. Theis | General Contact | NASA Goddard Space Flight Center | theis@carioca.gsfc.nasa.gov |