[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

[PEM12-13] Circulation at the Edge of Space: Lower-thermospheric Winter-to-Summer Circulation

★Invited Papers

*Jack Chieh Wang^1,2、Jia Yue^1,2、Wenbin Wang³、Liying Qian³、McArthur Jones⁴、Qian Wu³、Ningchao Wang⁵ (1.Goddard Space Flight Center, NASA, MD, USA、2.Catholic University of America, DC, USA、3.High Altitude Observatory, NCAR, CO, USA、4.U.S. Naval Research Laboratory, DC, USA、5.Langley Research Center, NASA, VA, USA)

キーワード：Residual Circulation, Lower Thermosphere, Whole-atmosphere Coupling

Observations of tracer gas distribution and numerical experiments suggest an existence of a reversed meridional circulation in the lower thermosphere (~90-130 km height), stacked between the well-known mesospheric and middle-to-upper thermospheric summer-to-winter circulations. It has been found that this lower-thermospheric winter-to-summer circulation might play a significant role in the seasonal and latitudinal variation of the thermospheric density, composition, and in turn drives the variability of the ionospheric plasma density.

In this study, the forcing mechanism of the lower-thermospheric circulation is investigated using the Specified Dynamics configuration runs of the Whole Atmosphere Community Climate Model eXtended (SD-WACCMX). The result suggests that the circulation is mainly driven by the momentum deposition from tides and resolved inertia gravity waves. The lower-thermospheric circulation is found to be the main driver of the intra-annual variation of the atomic oxygen between ~95-130 km compared to the eddy and molecular diffusion, contrary to the previous hypothesis. Our analysis indicates the vertical advective process can effectively transport the atomic oxygen from its source to sink. This study underscores the importance of the whole atmospheric coupling through the wave propagation and dissipation. It also demonstrates that the wave forcing from the lower atmosphere needs to be accurately represented in the models in order to simulate the ionosphere and thermosphere accurately.