Ionosphere-thermosphere global time response to geomagnetic storms

TL;DR

This study analyzes the global thermosphere response to geomagnetic storms using satellite data, revealing significant heating in high-latitude regions and asymmetries related to magnetic conditions during storms.

Contribution

It provides a comprehensive analysis of thermospheric density changes during 168 geomagnetic storms, highlighting the timing, magnitude, and asymmetries of heating effects.

Findings

High-latitude thermosphere heats rapidly within 1.5 hours of storm onset.

Joule heating increases by approximately 200% during storms.

Asymmetry in heating linked to magnetic field components, especially B_y.

Abstract

In this study, we investigate thermospheric neutral mass density heating associated with 168 CME-driven geomagnetic storms in the period of May 2001 to September 2011. We use neutral density measured by two low-Earth orbit satellites: CHAMP and GRACE. For each storm, we superpose geomagnetic and density data for the time when the IMF B$_\mathrm{z}$ component turns sharply southward chosen as the zero epoch time. This indicates the storm main phase onset. We find that the average SYM-H index reaches the minimum of $-$42 nT near 12 hours after storm main phase onset. The Joule heating is enhanced by approximately 200\% in comparison to quiet values. In respect to thermosphere density, on average, high latitude regions (auroral zones and polar caps) of both hemispheres are highly heated in the first 1.5 hour of the storm. The equatorial response is presumably associated with direct equator-ward propagation of TADs (traveling atmospheric disturbances). A slight north-south asymmetry in thermosphere heating is found and is most likely due to a positive B$_\mathrm{y}$ component in the first hours of the storm main phase.