The signature of H+ in the equatorial anomaly: An empirical model

Abstract

The task of developing empirical models of the thermal ion composition is complicated by the presence of both short‐term temporal and localized spatial variations in the constituents. The requirements of a detailed numerical representation of variable composition patterns such as those detected in the zone of the equatorial anomaly (EA) may exceed either the statistical data available or the numerical modeling resolution, or both. As an illustrative example a correlative test of a parameterized spherical harmonic expansion model of Ogo 6 dayside measurements of n(H+) is performed, particular characteristics of the observations being used as a basis for comparison. Whereas a review of other research confirms that the Ogo 6 observations of EA variability in longitude and local time are generally consistent with independent experimental and theoretical results, the model reproduces the observed broad‐scale longitudinal behavior but falls short of representing some details of these features. Specifically, the model depicts the persistent prominence of the EA development in the eastern Asian longitude zone relative to the eastern American longitude zone, as Well as the longitudinal shift in the hemispheric asymmetry in EA crests, although the amplitudes of some observed features are not precisely modeled. These results emphasize (1) the limitation in statistical coverage from a single satellite for identifying complex localized and short‐term ionospheric variations and (2) the need for integrating dynamic parameters, e.g., neutral wind and electric field‐ion drift terms, to produce a hybrid empirical‐analytical model.