| dc.description.abstract | The genesis and intensification of tropical cyclone(TC) are usually occurring in the ocean where is lacking those traditional observations like surface in-situ data or radiosounde for upper atmosphere. Therefore, satellite data plays a critical role in the purpose of simulation and/or forecast of TC in these stages, and the further investigation of the evolution and intensity intensification. According to the earlier studies, part of the energy for TC intensification is associated with the planetary boundary processes, which might be through the air-sea interaction like latent heat flux and sensible heat flux. Furthermore, sea surface wind could be an important role between sea and air when gradient is presented. Therefore, sea surface wind data from the Advanced Scatterometer (ASCAT) which is aboard on ESA Metop-A satellite are used to address this issue in this study through the data assimilation technique and the use of regional Weather Research and Forecasting (WRF) model. The main focus is placed on the investigation of the impacts from sea surface wind, sensible heat flux, and latent heat flux for the TC forecast. The discussion on the relative importance of those above fluxes during the TC intensification stage.
This study is divided into two parts: data assimilation experiment and sensitivity experiment. Typhoon Nuri (2008) in the northwestern Pacific Ocean is chosen to elaborate those fluxes and roles as described. In first part of experiment, the best forecast skill is from the use of ASCAT and traditional observation data sets, by examination of the TC’s intensity and track forecasts. This is due to the ASCAT data can improve the structure of surface wind in the initial time.
In second part, the sensitivity experiment, we find the higher sea surface temperature might increase the temperature gradient between the sea and the air. It leads an increased air-sea flux and a stronger TC in the later forecast hours. It is also found that the sea surface wind plays an important role in the sea-air flux, that is, if there is a large temperature or humidity gradient between sea and air, the energy conversion efficiency will be poor due to the weak sea surface wind speed. Thus, TC obtains less energy from the ocean and the intensity will not be intensified. Cross-analysis of the above simulations, we conclude that the larger fluxes in the early stage of the Typhoon Nuri, the more energy can be obtained from the ocean and the intensity will become stronger.
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