Pioneer Venus Orbiter Measurements of Solar EUV Flux During Solar Cycles 21 and 22

The Pioneer Venus Orbiter (PVO) had on board the electron temperature probe experiment which measured temperature and concentration of electrons in the ionosphere of Venus. When the probe was outside the Venus ionosphere and was in the solar wind, the probe current was entirely due to solar photons striking the probe surface. This probe thus measured integrated solar EUV flux (Ipe) over a 13-year period from January 1979 to December 1991, thereby covering the declining phase of solar cycle 21 and the rising phase of solar cycle 22. In this paper, we examine the behavior of Ipe translated to the solar longitude of Earth (to be called EIpe) during the two solar cycles. We find that total EUV flux changed by about 60% during solar cycle 21 and by about 100% in solar cycle 22. We also compare this flux with other solar activity indicators such as F_10.7 , Lα, and the solar magnetic field. We find that while the daily values of EIpe are highly correlated with F_10.7 (correlation coefficient 0.87), there is a large scatter in EIpe for any value of this Earth-based index. A comparison of EIpe with SME and UARS SOLSTICE Lα measurements taken during the same period shows that EIpe tracks Lα quite faithfully with a correlation coefficient of 0.94. Similar comparison with the solar magnetic field (Bs) shows that EIpe correlates better with Bs than with F_10.7 . We also compare EIpe with total solar irradiance measured during the same period.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43713/1/11207_2004_Article_140430.pd

Impact ionization in lower atmosphere of Venus

230-233The high energy particles (electrons and protons) passing through the lower atmosphere of Venus are attenuated and produce ionization of atmospheric constituents. In this paper, the loss of energy of electrons (105 E 8 eV), protons (107 E 12 eV), and Bremsstrahlung radiation due to electrons of energy 104 E 8 eV have been computed. The results are used to study the impact and Bremsstrahlung photoionization in lower ionosphere of Venus. The production rate due to the attenuation of energetic particles has been evaluated. It is shown that the production rate due to non-relativistic protons is dominating above 100 km, whereas below this height extreme relativistic protons are effective and produce a peak at the height of 65 km