An Extreme Events Study of the Storm‐Time Variations in Satellite Drag Coefficients
Journal Article
Overview
abstract
Abstract; This study examines storm‐time variations in the drag coefficients of the GRACE and GRACE Follow‐On (FO) satellites during selected extreme geomagnetic storms—the October 2003, November 2003, November 2004, and May 2024 storms. Orbit‐averaged values derived using closed‐form solutions show a 6%–12% decrease during the main phase of the storms. The storm‐time variations in are primarily driven by (a) decreases in atomic oxygen (O) mole fraction with corresponding increases in nitrogen mole fraction, and (b) higher accommodation levels resulting from enhanced O density and neutral temperature. The drag coefficients are calculated using the neutral outputs from the NRLMSIS, GITM, and TIEGCM atmospheric models. The drag coefficients derived from GITM show the maximum storm‐time variations (8%–12%), due to lower pre‐storm O density and temperature, resulting in lower accommodation coefficients and greater sensitivity of gas‐surface interaction (GSI) to storm‐induced thermospheric changes. The drag coefficients are calculated using Diffuse Reflection with Incomplete Accommodation (DRIA) and Cercignani–Lampis–Lord (CLL) GSI models, which show similar storm‐time variations with larger quiet‐time differences that reduce after storm onset. A comparison of GRACE during the October 2003, November 2003, and November 2004 storms shows the lowest variation for October 2003 storm (5%–6%) and the highest variation for November 2004 storm (11%–12%). These differences occur because storms with higher F10.7 indices, such as the October 2003 storm (daily F10.7 = 275 sfu), correspond to more heated background thermosphere; hence the storm‐induced changes produce smaller relative variations in .
