Publication Date:
2011-05-24
Description:
The equatorial mass density anomaly (EMA) is a fascinating phenomenon in the equatorial upper atmosphere. In this study, we investigate the generation mechanism of the EMA using the ground-to-topside model of the atmosphere and ionosphere for aeronomy (GAIA). The GAIA model is a self-consistent global model of the atmosphere and ionosphere covering the height range from the ground surface to the exobase. It can reproduce the observed EMA structure at 300–400 km heights. Our results show that the EMA structure can extend down to 200 km height. The EMA during daytime is caused by the in situ diurnal tide and the upward propagating terdiurnal tide. About half of the magnitude of the EMA is generated by the upward propagating terdiurnal tide from the lower atmosphere. This is the first report concerning the importance of the upward propagating tide for EMA formation. The in situ diurnal tide in the thermosphere is also essential for EMA formation. The in situ diurnal tide is modified by the momentum exchange between the plasma and the neutral atmosphere. This is seen as the enhanced upward flow of the neutral atmosphere along the dip equator in the 200–400 km height region, which has a profound effect on the latitudinal distributions of the atmospheric composition, temperature, pressure, and density in the thermosphere.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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