A comparison of solar EUV flux from Langmuir probe photoelectron measurements on the Pioneer Venus Orbiter with other solar activity indicators

Abstract

The electron temperature probe acted as a photo-diode on the Pioneer Venus Orbiter (PVO) and measured the integrated solar EUV flux (I_pe) over a 13 year period from January 1979 to December 1991, thus covering the declining phase of solar cycle 21 and the rising phase of solar cycle 22. Gross features in the solar activity variations of this flux during the 13 year period have earlier been studied by Brace et al. (1988) and Hoegy et al. (1993). In this paper, we study the fine features by translating the observed I_pe to the solar longitude of Earth (to be called as EI_pe) and comparing it with other solar activity indicators like F_10.7, Lyman alpha and the solar magnetic field. We find that while the daily values of EIpe are highly correlated with F10.7 (correlation coefficient 0.87), there is a large scatter in EI_pe for any value of this earth based index. Comparison of EI_pe with SME and UARS-SOLSTICE Lyman-alpha measurements taken during the same period indicates that EI_pe tracks Lyman-alpha quite faithfully. Similar comparison with the solar magnetic field (Bs) shows that EI_pe correlates better with B_s than with F10.7.