Thermal and dynamical changes of the zonal mean state of the thermosphere during the 2009 SSW: GAIA simulations

摘要

Changes of the zonal mean state of the thermosphere during the 2009 stratospheric sudden warming (SSW) have been investigated using the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) model. Both the zonal mean thermal and dynamical structure of the thermosphere exhibit pronounced changes during the SSW in terms of zonal mean temperature and winds. First, the zonal mean temperature above 100 km altitude drops at all latitudes except for in a narrow band around 60?N. Such temperature perturbations are found to be dominantly caused by changes in direct heating/cooling processes related to solar radiation and thermal heat conduction at high latitudes, but by dynamical processes in tropical regions. Second, the zonal mean zonal wind experiences a strong westward perturbation in the tropical thermosphere, along with distinct change in the meridional circulation. This change consists of two parts. One is a global scale north-to-south flow accompanied with upwelling/downwelling in the northern/southern polar region, the other is a fountain-like flow in tropical lower thermosphere. The large enhancement of semidiurnal tides is suggested to be the primary cause for the fountain-like flow.