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Earth Planets Space, Vol. 61 (No. 4), pp. 463-470, 2009

Global distribution of the thermospheric disturbances produced by effects from the upper and lower regions: simulations by a whole atmosphere GCM

Hitoshi Fujiwara1 and Yasunobu Miyoshi2

1Department of Geophysics, Graduate School of Science, Tohoku University, Sendai, Japan
2Department of Earth and Planetary Science, Faculty of Sciences, Kyushu University, Fukuoka, Japan

(Received September 30, 2007; Revised February 10, 2008; Accepted May 30, 2008; Online published May 14, 2009)

Abstract: It is well-known that low-latitude ionospheric/thermospheric disturbances are sometimes generated in association with the passage of traveling ionospheric/atmospheric disturbances (TIDs/TADs) produced in the high-latitude region and that the low-latitude ionosphere/thermosphere should be strongly coupled with the lower atmosphere. These facts suggest that the appearance of thermospheric disturbances with complex structures in the low-latitude region are the result of a superposition of disturbances which have different origins. We have investigated the lower atmospheric effects on the morphology of the thermospheric disturbances in response to changes in the geomagnetic activity by using a whole atmosphere general circulation model (GCM). In order to suppress the lower atmospheric effects, we set the global mean temperature and zero-wind below about 80-km altitude in the GCM. The simulation results show that the lower atmospheric effects can produce latitudinal and longitudinal structures in the low-latitude thermosphere. These lower atmospheric effects also modulate the amplitudes and structures of TADs propagating from the high- to low-latitude regions. Our results suggest that the lower atmospheric effects can produce variability in the TIDs/TADs, which in turn would create conditions conducive to plasma instabilities in the low-latitude ionosphere.
Key words: Thermosphere, GCM, simulation, traveling atmospheric disturbances (TADs), atmospheric coupling.


Corresponding author E-mail: fujiwara@pat.geophys.tohoku.ac.jp


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