Thermospheric mass density variations during geomagnetic storms and a prediction model based on the merging electric field

R Liu,S.-Y Ma,H Lühr,E Doornbos

doi:10.5194/angeo-28-1633-2010

Abstract

Abstract. With the help of four years (2002–2005) of CHAMP accelerometer data we have investigated the dependence of low and mid latitude thermospheric density on the merging electric field, Em, during major magnetic storms. Altogether 30 intensive storm events (Dstmin<−100 nT) are chosen for a statistical study. In order to achieve a good correlation Em is preconditioned. Contrary to general opinion, Em has to be applied without saturation effect in order to obtain good results for magnetic storms of all activity levels. The memory effect of the thermosphere is accounted for by a weighted integration of Em over the past 3 h. In addition, a lag time of the mass density response to solar wind input of 0 to 4.5 h depending on latitude and local time is considered. A linear model using the preconditioned Em as main controlling parameter for predicting mass density changes during magnetic storms is developed: ρ=0.5 Em + ρamb, where ρamb is based on the mean density during the quiet day before the storm. We show that this simple relation predicts all storm-induced mass density variations at CHAMP altitude fairly well especially if orbital averages are considered.

Highlights

The variation of the thermospheric mass density during geomagnetic storms is a rather complex phenomenon
In this study we aim to investigate, how the thermospheric density responds to solar wind inputs as quantified by the merging electric field, Em, during magnetic storms
30 major geomagnetic storms are chosen with their minimum Dst < −100 nT

Summary

Introduction

The variation of the thermospheric mass density during geomagnetic storms is a rather complex phenomenon. Both the density and the composition experience a series of dramatic changes. Many atmospheric models are developed with the purpose of predicting the mass density as close as possible. Moe and Moe developed a global density model in 1975, based on measurements of Spades and Logacs satellites (Moe et al, 1977). Hedin, 1991; Picone et al, 2002), based on incoherent scatter radar measurements of temperature and in situ satellite measurements of density and composition, try to consider the magnetospheric and solar influence as good as possible More recent models like the MSIS series (e.g. Hedin, 1991; Picone et al, 2002), based on incoherent scatter radar measurements of temperature and in situ satellite measurements of density and composition, try to consider the magnetospheric and solar influence as good as possible

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