In this work, we investigate the longitudinal patterns of thermospheric zonal winds (~400 km) and their seasonal and solar activity dependence using CHAllenging Minisatellite Payload cross‐track wind data and Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations. CHAllenging Minisatellite Payload data show that there are large longitudinal variations in thermospheric zonal winds. 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 at other longitudes. The nighttime zonal wind direction with pattern 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, including positive and negative peak locations, 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 longitudinal patterns during the June solstice are 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 results shows that geomagnetic field structure is the main cause of the large longitudinal variations of thermospheric zonal winds and their local time, hemispheric asymmetry, and seasonal changes at low and middle latitudes.

Observations from lidars and satellites have shown that large neutral temperature increases and decreases occur in the middle and low latitudes of the mesosphere and lower thermosphere region during geomagnetic storms. Here we undertake first‐principles simulations of mesosphere and lower thermosphere temperature responses to storms using the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model to elucidate the nature and causes of these changes. Temperature variations were not uniform; instead, nighttime temperatures changed earlier than daytime temperatures, and temperatures changed earlier at high latitudes than at low ones. Furthermore, temperatures increased in some places/times and decreased in others. As the simulation behaves similar to observations, it provides an opportunity to understand physical processes that drive the observed changes. Our analysis has shown that they were produced mainly by adiabatic heating/cooling that was associated with vertical winds resulting from general circulation changes, with additional contributions from vertical heat advection.

In this study, the effect of disturbance dynamo electric field (DDEF) induced by subauroral polarization streams (SAPS) on the variations of the equatorial electrojet (EEJ) and its counter electrojet (CEJ) during the geomagnetic storm on June 1, 2013 is analyzed in detail for the first time. Observations from ground‐based magnetometers showed that the SAPS‐induced EEJ flows westward and eastward in the daytime and dawn/dusk sectors, respectively. The effects of SAPS on EEJ are mainly associated with the changes of zonal ionospheric electric field, while the changes in the ionospheric conductivity play a secondary role. By using Thermosphere Ionosphere Electrodynamic General Circulation Model simulations, the zonal electric field induced by SAPS associated with the DDEF is examined. The results of the simulations show that the DDEF has a significant impact on the EEJ variability. The daytime westward EEJ at the dip equator is mainly driven by disturbance zonal wind, with secondary contributions from disturbance meridional wind. A similar mechanism can be observed in the dawn/dusk sector when the eastward EEJ is produced; however, it has a much weaker intensity than that during the daytime.

Previous studies mostly focused on ionosphere and thermosphere responses to strong southward interplanetary magnetic field (IMF) B_z conditions. However, it is not clear how the ionosphere and thermosphere (IT) system responds to Alfvénic quasi‐periodic oscillating IMF B_z conditions. In this article, simulations by the Coupled Magnetosphere Ionosphere Thermosphere model have been used to investigate the effects of IMF B_z temporal variations with 10‐, 30‐, and 60‐min oscillation periods on the coupled IT system. The simulation results show that the cross polar cap potential and auroral peak electron energy flux are stronger when the IMF B_z oscillation frequency is lower. The relatively small periodic wind responses in the 10‐min IMF oscillation case indicates a low‐pass filter nature of the magnetosphere‐ionosphere‐thermosphere system. Two different thermospheric wind (Vn) responses are revealed. One is the almost simultaneous responses at all latitudes, and the other shows a typical traveling atmospheric disturbances signature with a time delay with respect to the latitude for all UTs. The simultaneous Vn responses at all latitudes appear in the daytime Northern Hemisphere, which are mainly caused by the ion drag force in association with penetration electric fields induced plasma density and ion drifts changes. The short‐period traveling atmospheric disturbances occurring in the nighttime of both hemispheres and the daytime of the Southern Hemisphere propagate from high to low latitudes showing latitudinal dependence. Both responses oscillate with the same frequencies as those of IMF B_z oscillations.