Hemispheric Differences in the Response of the Upper Atmosphere to the August 2011 Geomagnetic Storm: A Simulation Study

TL;DR

This simulation study analyzes the hemispheric differences in the thermosphere-ionosphere response to the August 2011 geomagnetic storm, revealing significant temperature, flow, and heating variations between hemispheres.

Contribution

It provides a detailed simulation-based analysis of hemispheric asymmetries in thermosphere-ionosphere responses during a major geomagnetic storm.

Findings

High-latitude ion flows increased by up to 180% during the storm

Global mean neutral temperature rose by up to 15%, with higher increases in the Southern Hemisphere

Hemispheric differences in flows and temperature were significant during storm phases

Abstract

Using a three-dimensional nonhydrostatic general circulation model, we investigate the response of the thermosphere-ionosphere system to the 5-6 August 2011 major geomagnetic storm. The model is driven by measured storm-time input data of the Interplanetary Magnetic Field (IMF), solar activity, and auroral activity. Simulations for quiet steady conditions over the same period are performed as well in order to assess the response of the neutral and plasma parameters to the storm. During the storm, the high-latitude mean ion flows are enhanced by up to 150-180%. Largest ion flows are found in the main phase of the storm. Overall, the global mean neutral temperature increases by up to 15%, while the maximum thermal response is higher in the winter Southern Hemisphere at high-latitudes than the summer Northern Hemisphere: 40% vs. 20%increase in high-latitude mean temperature, respectively. The global mean Joule heating increases by more than a factor of three. There are distinct hemispheric differences in the magnitude and morphology of the horizontal ion flows and thermospheric flows during the different phases of the storm. The largest hemispheric difference in the thermospheric circulation is found during the main and recovery phases of the storm, demonstrating appreciable geographical variations. The advective forcing is found to contribute to the modeled hemispheric differences.