| 摘要: | 研究期間：10108~10207;Mesosphere, the coldest part of the atmosphere, has been investigated using many ground based instruments like lidars, airglow photometers, imagers etc., that provide data over specific locations confined to land. A few in situ investigations also have been done using rockets. On the other hand observations from a satellite platform provide global data. The SABER instrument onboard the TIMED satellite has been providing valuable data for the study of the atmosphere from 20 to 120 km since its launch in December 2001. Investigations using this satellite data have provided new results and insights and a better understanding to the atmospheric science community. Presently it stands as one of the largest global database with observations of the Earth’s atmosphere for 10 years. We propose to use this long term data to investigate the mesosphere in detail on the global scale, specifically, the temperature structure, and the gravity wave (GW) activity of the region. Recent studies have shown that the mesopause over tropics and sub tropics is always at around 100 km. While the sub tropical mesopause showed a seasonal variation, none was observed over the tropics. Earlier studies at mid- and high-latitudes also showed large seasonal variations in the mesopause temperature and altitude. In this study we would like to investigate the long term global mesospheric temperature distributions and to understand how the seasonal variations change with latitude. Another important aspect of the mesosphere is the GW activity. The GWs are produced in the lower atmosphere and travel to mesospheric altitudes, break at these heights and deposit the energy and momentum they have been carrying from the lower altitudes. This wave breaking leads to the generation of secondary waves that travel further up to ionospheric F-region heights. It is now believed that over the tropical regions, GWs are the seeding mechanism in the generation of the equatorial spread-F and other ionospheric irregularities at various latitudes which in turn have effect on satellite communications, GPS etc. Models assume a set of GW parameters and try to understand these latter effects. In the present study we would like to investigate the GW activity in the mesosphere which is the basic cause and define the GW parameterization empirically, which will give a more realistic picture. This study will thus have a tremendous impact on ionospheric modeling studies. We would also investigate the effect of GW breaking on the mesospheric temperature inversions (MTIs) – the amplitude, width and height of occurrence, etc. – on the global scale. The actual cause or the source of energy for MTIs is still being debated. GW breaking and chemical heating are two important plausible mechanisms. The altitudes of GW breaking and occurrence of MTIs are similar and thus led to the belief that the wave breaking provides the required energy for the temperature enhancements in the MTIs. A correlation study will thus provide a statistical picture of the relation between the GW activity and the inversions. Most importantly we would also investigate the source of the GWs in the lower atmosphere and try to understand the differences and the similarities in the GW features produced due to various mechanisms like deep convections, extreme weather events like cyclones, dust storms, etc and investigate in what way they effect the mesosphere. Differences in the strength of the GW activity may arise due to different sources and/or due to different magnitude of the same source during different events. An attempt would be made to quantify such effects. |
