Daytime F region ion energy balance at Arecibo for moderate to high solar flux conditions

Abstract

Ion energy balance studies using incoherent scatter radar (ISR) data involve the estimation of the neutral density and exospheric temperature from the ISR-measured parameters using theoretical collision cross sections. The ratio [O]radar/[O]MSIs in long-term averages is an estimate of the so-called Burnside factor and can be derived from these studies. This parameter is thought to be associated with errors in the O+-O collision cross section. The most recent comparison between the Mass Spectrometer Incoherent Scatter (MSIS) neutral atomic oxygen densities and values derived from Arecibo ISR measurements using ion energy balance shows large discrepancies for high solar flux conditions. In contrast to ion momentum studies, which typically lead to a Burnside factor greater than 1 (usually near 1.2-1.3), the discrepancies between MSIS densities and radar-derived values tend to result in low values (near 0.8) for the Burnside factor. Various interpretations of this discrepancy have been put forward. We have reanalyzed the Arecibo ISR World Day data from 1988 to 1994, corresponding to the moderate to high solar flux period of solar cycle 22. By extending the analysis to the upper F region/lower topside (and explicitly including the role of H +, which is often neglected) we obtain consistent results for the neutral density and exospheric temperature that show no significant long-term discrepancy from the MSIS predictions. For this period, we obtain a median ratio [O]radar/[O]MSIs of 1.26 ±0.02 using the O +-O collision cross section from Banks (1966). The standard deviation of the data is about 0.35. This ratio is close to the most recently published theoretical simulations of the collision cross section within the uncertainties. Knowing the correct O+-O collision cross section allows one to extract the neutral parameters from the radar data and study short-term (day-to-day) variations in those parameters. Copyright 2006 by the American Geophysical Union.