| dc.description.abstract | With the improvement of observation techniques and physical theories, scientists became more familiar with the gravity waves, a key factor of the atmospheric dynamics. In the past, atmospheric profiles were not supportive enough for us to conduct research on some hard-to-reach areas, such as the oceans and the Polar regions. Data shortage has caused many difficulties in climate studies until the launch of Formosat-3 in April, 2006. The constellation consists of six Low Earth Orbit (LEO) satellites at the height of 800 km, providing 2000 to 2500 soundings per day. The main scientific goal is to utilize the radio occultation (RO) signals to infer the atmospheric parameters, including refractivity, temperature, pressure, and relative humidity fields. The FORMOSAT-3/COSMIC has provided a very favorable data platform to perform the investigation of the gravity wave activities.
This paper is focused on the studies of the seasonal variations of gravity wave activities using the temperature profiles obtained by the FORMOSAT-3/COSMIC RO technique at height of 20~40 km, from September 2006 to December 2009. The average potential energy (AveEp) of the gravity waves was estimated to quantify the seasonal variations and compare those between Asian and Australian Monsoon regions（45°N~45°S, 60°E~160°E）. The study area was divided into 30 non-overlapped regions, each representing a 15 by 20 degree grid, in latitude and longitude, respectively. We compared those grids in different latitudinal intervals over different geographic locations. The result showed that the larger AveEp values of the 15°N~30°N and 15°S~30°S intervals occurred in summer - JJA for the northern hemisphere and DJF for the southern hemisphere. However, for 30°N~45°N and 30°S~45°S intervals, larger AveEp values appeared in winter - DJF for the northern hemisphere and JJA for the southern hemisphere. Furthermore, the spatial analysis of gravity wave activities indicated that within the higher AveEp value latitudinal intervals, the largest AveEp value located at the Indian Peninsula in the northern hemisphere summer (JJA) and Northern Australia in the southern hemisphere summer (DJF). In this study, we also found that the AveEp values were much higher than those in 07/08DJF and 08MAM. We believed the gravity anomalies were attributed to the strengthening of the Walker Circulation, which was caused by the La Nina phenomenon.
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