An observational test of the Tsyganenko (T89a) model of the magnetospheric field

Abstract

The range of magnetic field tilt angles observed at several satellites in geosynchronous orbit is compared with the ranges predicted for the same locations by the different Kp parameterizations of the Tsyganenko 1989a magnetic field model as a function of local time and season. The data are examined separately for satellite locations near the magnetic equator and slightly off the equator. The model predicts reasonably well the observed basic variation in the tilt angle with location, and it permits a range of field inclinations adequate to encompass the majority of the observed angles for the dawn, dusk, and night quadrants. On the day side of the magnetosphere the model exhibits very little variation in tilt over the entire range of parameterizations and cannot reproduce the observed range of tilt angles. Near the magnetic equator the majority of observed tilt angles lie within the model range, with roughly equal numbers of cases that are overstretched or understretched with respect to the model range. Off the equator the models tend to be more stretched than is generally observed. With some modest season‐to‐season differences these results are valid for all four seasons.