Determination of the Mysterious O+-O Collision Frequency Factor From the Sanya Incoherent Scatter Radar Measurements

Collisions between oxygen atoms and oxygen ions play a crucial role in the momentum and energy exchange between the ionosphere and the thermosphere. However, direct measurement of O⁺-O collision frequency or parameterizing this factor has been challenging over years. By utilizing the newly built Sanya incoherent scatter radar wind profiles, we have proposed a new method to calculate the O⁺-O collision frequency factors, that is, Burnside factor, for the first time from the whole year SYISR data set. Our results show that the mean Burnside factor is 1.31, although it ranges from 1.07 to 1.41 as a function of local time and from 1.19 to 1.41 with respect to the seasons. The reliability of the method has been validated through an independent estimation by a co-located Fabry-Perot interferometer and SYISR winds. To our knowledge, this is the first comprehensive analysis of Burnside factor, which are of great importance in collision frequency parameterization.