A Predictive Model of Geosynchronous Magnetopause Crossings

TL;DR

This paper presents a predictive model for geosynchronous magnetopause crossings based on solar wind and geomagnetic data, capturing dawn-dusk asymmetry and Bz saturation effects, with improved prediction capabilities for space weather forecasting.

Contribution

The paper introduces a new model that accurately predicts magnetopause crossings by incorporating asymmetry and saturation effects, based on extensive observational data from 1994-2001.

Findings

Magnetopause dawn-dusk asymmetry depends on Bz polarity.

Negative SYM-H reduces the solar wind pressure needed for crossings.

Magnetic storm conditions cause saturation of Bz influence on magnetopause position.

Abstract

We have developed a model predicting whether or not the magnetopause crosses geosynchronous orbit at given location for given solar wind pressure Psw, Bz component of interplanetary magnetic field (IMF) and geomagnetic conditions characterized by 1-min SYM-H index. The model is based on more than 300 geosynchronous magnetopause crossings (GMCs) and about 6000 minutes when geosynchronous satellites of GOES and LANL series are located in the magnetosheath (so-called MSh intervals) in 1994 to 2001. Minimizing of the Psw required for GMCs and MSh intervals at various locations, Bz and SYM-H allows describing both an effect of magnetopause dawn-dusk asymmetry and saturation of Bz influence for very large southward IMF. The asymmetry is strong for large negative Bz and almost disappears when Bz is positive. We found that the larger amplitude of negative SYM-H the lower solar wind pressure is required for GMCs. We attribute this effect to a depletion of the dayside magnetic field by a storm-time intensification of the cross-tail current. It is also found that the magnitude of threshold for Bz saturation increases with SYM-H index such that for small negative and positive SYM-H the effect of saturation diminishes. This supports an idea that enhanced thermal pressure of the magnetospheric plasma and ring current particles during magnetic storms results in the saturation of magnetic effect of the IMF Bz at the dayside magnetopause. A noticeable advantage of the model prediction capabilities in comparison with other magnetopause models makes the model useful for space weather predictions. Supplement : a program-code of the GMC-model