The longitudinal variations of upper thermospheric zonal winds observed by the CHAMP satellite at low and mid-latitudes

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Thursday, March 1, 2018

In this work, Kedeng Zhang, Wenbin Wang and others, investigate the longitudinal patterns of thermospheric zonal winds (~400 km) and their seasonal and solar activity dependence. This is accomplished by using CHAllenging Minisatellite Payload (CHAMP) cross-track wind data and Thermosphere Ionosphere Electrodynamics General Circulation model (TIEGCM) simulations.

Longitudinal structures of zonal winds image
Longitudinal structures of zonal winds observed by the CHAMP satellite (left), simulated by TIEGCM with the IGRF magnetic field (case 1, middle) and from TIEGCM simulations with an aligned dipole magnetic field (case 2: right) in the mid-latitude region of the northern hemisphere (top) and in the EIA region of the southern hemisphere (bottom) at solar maximum. The black dotted contours show the zero value of the relative wind speed. The maximum and minimum values for each case are also given in each plot. Note that the contour levels in the right panel are different from those in the other two plots.

CHAMP data show that there are large longitudinal variations in thermospheric zonal winds. However, these longitudinal variations do not have significant solar activity dependence. In the northern hemisphere at low and middle latitudes, the daytime zonal winds are more westward between -90° and 90° longitudes and more eastward in other longitudes. The nighttime zonal pattern of winds is opposite to that in the daytime. In the southern hemisphere at low and middle latitudes the local time variation of the longitudinal wind structure is almost the reverse of that in the northern hemisphere. Thus, the zonal wind patterns also show great hemispheric asymmetry. In addition, the longitudinal patterns of zonal winds in both hemispheres show seasonal variations. The June solstice longitudinal pattern of the zonal winds is significantly different from those in other seasons. These observational results are well reproduced in TIEGCM simulations. To elucidate the physical processes responsible for the observed and simulated longitudinal patterns of the zonal winds, the TIEGCM is also run for different geomagnetic field configurations. A comparison between the TIEGCM simulations shows that the magnetic field structure is the main cause of the large longitudinal variations of thermospheric zonal winds and their local time, hemispheric asymmetry and seasonal changes.

Publication Name: J. Geophys. Res., Space Physics