Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsa31b1421m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SA31B-1421
Physics
[2437] Ionosphere / Ionospheric Dynamics, [3367] Atmospheric Processes / Theoretical Modeling, [3369] Atmospheric Processes / Thermospheric Dynamics, [3389] Atmospheric Processes / Tides And Planetary Waves
Scientific paper
Recent observational and modeling studies have revealed that the energy input from the lower atmosphere produces significant spatial and temporal variations in the thermosphere/ionosphere. For example, the CHAMP observation has shown that the distributions of the neutral temperature and electron density in the equatorial thermosphere/ionosphere have wave-4 pattern in the longitudinal direction. This wave-4 pattern is considered to originate from non-migrating diurnal tide (DE3) that is excited in the troposphere. However, the physical mechanism of spatial and temporal variations in the thermosphere/ionosphere caused by upward propagating atmospheric waves is not fully understood. In order to investigate the physical mechanism of these variations, we developed an atmosphere-ionosphere coupled model, in which a whole atmosphere general circulation model (GCM), an ionosphere model and an electrodynamics model are integrated. The whole atmosphere GCM contains the region from the ground surface to the upper thermosphere, so that we can simulate excitation of tides in the lower atmosphere and their upward propagation to the thermosphere. By using the coupled model, we investigate effects of upward propagating tides on longitudinal and temporal variations in the thermosphere/ionosphere. In particular, we examine effects of semidiurnal tides from the lower atmosphere on the variations at middle latitudes in the thermosphere/ionosphere. Our result shows that non-migrating semidiurnal tide produces longitudinal asymmetry of the neutral density and temperature distributions at middle latitudes in the thermosphere. We also discuss day-to-day variations of tides in the lower atmosphere and their relations with day-to-day variations of the longitudinal structure in the thermosphere. Moreover, our result shows that the meridional winds associated with non-migrating semidiurnal tides have the maximum near the equator (7-10 m/s), and induce north-south asymmetry of the wave-4 pattern of the electron density near the equator. Thus, not only non-migrating diurnal tides but also non-migrating semidiurnal tides affect the longitudinal structure in the thermosphere/ionosphere.
Fujiwara Hideaki
Jin Hongying
Miyoshi Yasunobu
Shinagawa Hiroyuki
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