Numerical modeling of solar wind influences on the dynamics of the high-latitude upper atmosphere

M Förster,A A Namgaladze,M Holschneider,B E Prokhorov

doi:10.5194/ars-10-299-2012

Abstract

Abstract. Neutral thermospheric wind patterns at high latitudes obtained from cross-track acceleration measurements of the CHAMP satellite above both polar regions are used to deduce statistical neutral wind vorticity distributions and were analyzed in their dependence on the Interplanetary Magnetic Field (IMF). The average pattern confirms the large duskside anticyclonic vortex seen in the average wind pattern and reveals a positive (cyclonic) vorticity on the dawnside, which is almost equal in magnitude to the duskside negative one. The IMF dependence of the vorticity pattern resembles the characteristic field-aligned current (FAC) and ionospheric plasma drift pattern known from various statistical studies obtained under the same sorting conditions as, e.g., the EDI Cluster statistical drift pattern. There is evidence for hemispheric differences in the average magnitudes of the statistical patterns both for plasma drift and even more for the neutral wind vorticity. The paper aims at a better understanding of the globally interconnected complex plasma physical and electrodynamic processes of Earth's upper atmosphere by means of first-principle numerical modeling using the Upper Atmosphere Model (UAM). The simulations of, e.g., thermospheric neutral wind and mass density at high latitudes are compared with CHAMP observations for varying IMF conditions. They show an immediate response of the upper atmosphere and its high sensitivity to IMF changes in strength and orientation.

Highlights

More than fifty years since the start of the space era with the first satellites, the efforts to understand our space plasma environment and the complexities of its link to solar activities, propagating by the solar wind past the Earth, increase continuously
The term space weather is defined as the conditions on the Sun and in the solar wind, Earths magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and endanger human life or health
As we focus in this study on Interplanetary Magnetic Field (IMF) dependencies and hemispheric differences, we primarily tested the Upper Atmosphere Model (UAM) performance under relatively stable IMF conditions

Summary

Introduction

More than fifty years since the start of the space era with the first satellites, the efforts to understand our space plasma environment and the complexities of its link to solar activities, propagating by the solar wind past the Earth, increase continuously. The dependencies are highly complex and many of them are still not understood in spite of many decades of research with several generations of space missions. Understanding this complexity is a fundamental problem in physics. This is the subject of space weather science, a relatively new field of research. We confine to investigations of solar wind and IMF forcing processes at the high-latitude upper atmosphere, conveyed by the complex magnetospheric current system and their concomitant electric fields. It is common view that this coupling occurs their applicability for space weather monitoring tasks, as well as for optimal measurement ranges and precision require-

Average neutral wind vorticity at high latitudes

30 Apr 2006 10–24 2311 2

First comparisons for stable IMF conditions

Discussion and Conclusions