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

Abstract

Abstract. The input of energy and momentum from the magnetosphere is most efficiently coupled into the high latitude ionosphere-thermosphere. The phenomenon we are focusing on here is the magnetospheric substorm. This paper presents substorm related observations of the thermosphere derived from the CHAMP satellite. With its sensitive accelerometer the satellite can measure the air density and zonal winds. Based on a large number of substorm events the average high and low latitude thermospheric response to substorm onsets was deduced. During magnetic substorms the thermospheric density is enhanced first at high latitudes. Then the disturbance travels at an average speed of 650 m/s to lower latitudes, and 3-4 h later the bulge reaches the equator on the night side. Under the influence of the Coriolis force the travelling atmospheric disturbance (TAD) is deflected westward. In accordance with present-day atmospheric models the disturbance zonal wind velocities during substorms are close to zero near the equator before midnight and attain moderate westward velocities after midnight. In general, the wind system is only weakly perturbed ( v y < 20 m/s) by substorms.

In-Situ CHAMP Observation of Ionosphere-Thermosphere Coupling

“…More details of this study can be found in Ritter et al (2010). Interestingly, in the post-midnight sector (bin 3) only marginal substorm-related thermospheric variations are recorded.…”

“…Ritter et al (2010) have deduced a mean propagation speed of 650 m/s from their observations. Furthermore they report a westward deflection of the travel path.…”

“…From that dependence they suggested a relation between the enhanced air density and substorm processes. In a dedicated statistical study Ritter et al (2010) investigated the thermospheric response to the substorm onset. CHAMP mass density and wind measurements were investigated for a large number of substorms.…”

“…In order to check that, Ritter et al (2010) had a look at zonal winds which are detectable by CHAMP. The same procedure as used for the density study was applied to the cross-track wind component.…”

Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

“…When interpreting these average values, we have to keep in mind that substorms are discrete events. It would be more appropriate to synchronize the nighttime current measurements with the occurrence and phase of a substorm, as was done, e.g., by Ritter et al (2010). Then the obtained FAC and Hall current measurements could be better related to the processes operating during substorms.…”