Global variation of water vapor using different observational platforms (Aqua, COSMIC, NCEP and ECMWF)
平成20 (2008) 年度ミッション専攻研究員
I. Venkata Subba Reddy
The spatial and temporal variations of water vapor are very important in understanding abnormal and forecasting weather and to study climate change as water vapor is one of the greenhouse gases and it releases latent heat through condensation. The water vapor distribution varies sharply in the vertical direction as evident in the many forms of stratiform cloud system. The importance of water vapor was well recognized theoretically and the observations were sparse in the past. But recently different observational techniques were evolved to probe the changes in the atmosphere on a global basis, irrespective of the weather conditions and to monitor continuously, with high temporal and spatial resolutions (both vertical and horizontal) and some of these techniques are self calibrated. The COSMIC, AQUA, NCEP and ECMWF data sets are useful to study the global variation of water vapor. Each data set has its own special features and these are useful to understand the water vapor globally more qualitatively and quantitatively. By taking the larger datasets causes for the variability of water vapor and the influence of water vapor on global climate change can be studied extensively.
In the recent years COSMIC, Aqua, missions have emerged as very powerful techniques to study water vapor globally. The mission provides ~2000 real-time soundings per day over the globe with high degree of vertical resolution and providing global coverage in all weather conditions. This GPS radio occultation data is ideally suited for a detailed study of water vapor. Aqua is another satellite mission of the NASA’s Earth Observing System (EOS) which was launched on May 04, 2002, consists of six distinct earth-observing instruments. The horizontal resolution of the AMSU data at nadir is 40.5 km, this is three times as coarse as the AIRS data.
The observational technique is different for both COSMIC and Aqua satellite. The COSMIC mission provides high vertical resolution data with limb technique but Aqua satellite provides high horizontal resolution data with nadir technique. By combining these two, both vertical and horizontal variation of water vapor will be studied globally. We are retrieving the water vapor with COSMIC data by using 1D-var analysis with JMA-GSM data as an Initial value. The retrieved WV profiles from the COSMIC 1D-var data are to be compared with the Aqua satellite as well s routine radiosonde observations at different latitudes. The NCEP reanalysis and ECMWF data will also be used for the comparison and the difference between these observations will be studied. The objective of the present research plan is to study the variation of WV globally as well as over the pacific region especially in the Indonesia over the latitude ±20° and longitude 90°–180° E. The area is choose because of where most of the times unusual weather systems will occur and it will causes the damage of social, economic and human activities. We are also focusing on the water vapor variation over the western pacific region. Because during El Niño episodes, on the equatorial sea surface temperatures (SSTs) are abnormally warm. During La Niña episodes, on the equatorial sea surface temperatures (SSTs) are abnormally cold from the eastward to the west coast of South America, and tropical rainfall and convection tends to be focused over the western equatorial Pacific and Indonesia. This pattern represents an amplification of climatological mean conditions, which feature heavy rainfall across Indonesia and little-to-no rainfall over the eastern equatorial Pacific. The annual and inter annual variability of water vapor globally as well as in the Western pacific region, with special emphasis over Indonesia will be studied. The connection between precipitation and El Niño-Southern Oscillation (ENSO) and their dominant mode of variability in western Pacific region will be studied in detail.