For given parameters of the interplanetary plasma near Earth the magnetic field in the magnetosheath can bc described by fluctuations superimposed upon an average static field configuration. Using potential theory, we derived analytical expressions describing the steady state magnetic field in the transition region between the bow shock and the magnetopause. The model contains five parameters, namely, the stand-off distance of the magnetopause, the stand-off distance of the bow shock, and the three components of the interplanetary magnetic field. The shape of the magnetopause and of the bow shock is modeled by a paraboloid with rotational symmetry around the Sun-Earth axis. Compared to other models, our procedure leads to simple analytical formulae which make it most suitable for studies of the effects of the magnetosheath on charged particle propagation.

We present orbit‐averaged geomagnetic transmission measurements during the large solar energetic particle events of October 1989 using proton data from the NOAA‐10 and GOES‐7 satellites. We compare the measurements to geomagnetic transmission calculations determined by tracing particle trajectories through the combination of the International Geomagnetic Reference Field (IGRF) model and the 1989 Tsyganenko magnetospheric magnetic field model. We modify the effective ‘ring current’ parameter in the 1989 Tsyganenko model based on the Dst data. We compare our results to calculations employing only the IGRF and to a parameterization of geomagnetically quiet‐time cutoff rigidities derived from Cosmos/Intercosmos observations. Our 3‐hour orbit‐averaged results have ∼15% accuracy during the October 1989 events.

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