Wind and temperature effects on thermosphere mass density response to the November 2004 geomagnetic storm

Abstract

[1] A unique conjunction of the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) and the Challenging Minisatellite Payload (CHAMP) satellites provided simultaneous columnar neutral composition, SO/N 2 , and thermosphere density observations, enabling a novel study of thermospheric response to the 7-9 November 2004 geomagnetic storm. Both SO/N 2 and mass density showed profound response to this severe geomagnetic storm, but their latitudinal and temporal structures differed markedly. In particular, high-latitude depletion and low-latitude enhancement in SO/N 2 were observed throughout the storm period, especially during the main phase. In contrast, neutral density at 400 km altitude increased from pole to pole shortly after the storm, with strongest enhancement of order 200%-400% during the main phase. Comparisons of observed thermosphere response with simulations from the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) were carried out to interpret the observed contrasting characteristics of thermosphere composition and mass density in response to this geomagnetic storm. The TIEGCM simulations show that the contrasting characteristics occur not only in SO/N 2 and mass density at a constant altitude at 400 km, but also in O/N 2 and mass density on a constant-pressure surface. At an altitude of 400 km (CHAMP altitude), storm-time mass densities significantly increase due to an increase in scale height throughout the vertical column between the heat source and satellite altitude. For a given increase in scale height, the more scale height increments separating the heat source from the satellite altitude, the greater is the mass density response. It is shown that scale height change is caused partly by storm-time neutral temperature enhancements due to heating and partly by changes in mean molecular weight due to winds. These findings indicate that wind effects can cause significant deviations from a mass density pattern resulting solely from neutral temperature changes by altering the mean molecular weight, particularly at high latitudes.

Substorm-related thermospheric density and wind disturbances derived from CHAMP observations

“…At a given altitude well above the heating region, the first effect always causes a mass density enhancement, while the second one may cause a density reduction due to a smaller scale height of the heavier particles. Both increases and decreases have been observed over active regions (Prölss, 1982;Prölss et al, 1988;Lei et al, 2010). This competition of effects may also explain the lack of density enhancement reflected by the green curve in the upper right frame of Fig.…”

Predicting storm-time thermospheric mass density variations at CHAMP and GRACE altitudes

“…Here we would like to repeat the important parts only briefly: the density measurements at mid and low latitudes (between ±60 • MLat) are averaged for each CHAMP/GRACE orbit; high latitude regions are excluded because the density here responds to heating and composition change during magnetic storms (e.g. Lei et al, 2010a). E m is integrated over a period of about 3 h. After this preconditioning E m is termed E m , which shows better correlation with ρ avg .…”

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

“…The high latitude area is omitted because during storm-time the heating in this area causes thermal expansion and thermospheric composition change. Therefore, at high latitude regions we may find density enhancements or depletions in response to Joule heating (e.g., Lei et al, 2010).…”