An updated study of the O+ - O collision frequency using corresponding FPI and ISR thermospheric wind experiments at Millstone Hill.

O+-O collision frequency is an important aeronomic parameter associated with upper atmospheric momentum and energy exchanges between O+ and O. In an analysis of Fabry-Perot Interferometer (FPI) and Incoherent Scatter Radar (ISR) data, Burnside [1987] suggested a modification factor (1.7) to the traditional value of O+-O collision frequency. Determining more accurately the Burnside Factor has been the subject for many prior studies with different techniques. This study revisits the Burnside Factor by using an extended FPI and ISR dataset from Millstone Hill. The FPI data used are from an updated high-resolution instrument, which began operation in 2009. The study included data from 95 nights between 2010 and 2015 when the FPI and ISR (with both zenith and steerable antennas) were all operating. Nights with high Ap were excluded, leaving 1235 data points in total. The same frequentist approach applied previously in Buonsanto et al. [1997] (using 21 experiments) yields similar right-skewed Burnside Factor distribution on this data. In this study we will discuss results derived using different statistical approaches, including median, mean, and the Bayes theorem. The latter method appears to give an estimated median well below 1.0.