Preliminary Study About Asymmetrical Structure Of Thermal And Its Impact On Tropical Cyclone Intensity

Structure change is one of the most important reasons which causes intensity change of tropical cyclone(TC). The relationship between the asymmetry and evolution characteristics of structure and intensity change is not yet very clear which is restricted intensity forecasting. Early studies often focus on the asymmetrical analysis of kinetic structure(winds), but research about thermal structure is relatively small(especially the specific humidity). As we all know, the release of latent heat of condensation is the main source of energy for the development of the TC, and the amount of water vapors indicates the level of humidity. So this article will combine temperature with humidity to analyze relationships between the asymmetrical structure of temperature and humidity and intensity change comprehensively. It including: the statistical characteristics of TC temperature and humidity structure on different intensity level, different life stage, different develop types, and the comparative analysis of temperature and humidity between rapid intensification and rapidly weaken. On this basis, we conduct numerical simulation on rapid intensification case of "Vicente", and diagnostic analysis the possible relationship between the asymmetrical structure evolution of temperature and humidity and rapid enhancement process.At first, synthetic analysis is used to study the asymmetrical structure about temperature and humidity of tropical cyclones over Western North Pacific Ocean and South China Sea during 1979-2010 years. The results show that: With the cyclones enhanced, the asymmetry of flow field is tending to axisymmetrization gradually, but the asymmetry of the specific humidity field in outsourcing and peripheral area towards to enhanced. Cyclones have a "double warm-core" of the non-uniform distribution of the vertical structure generally. The warm-core on low-level of weak tropical cyclones is relatively strong and the warm-core on high level of TY and more than TY level of tropical cyclones is relatively strong. The horizontal scope and shape of "warm-core" is becoming amplifying and circular with cyclones intensity increased. The "wet-core" of tropical cyclones is mainly located in the low level about 700-850 hPa. With the cyclones intensity growing, the intensity of wet-core is increasing and the scope of 0.8 g.kg-1 anomaly specific humidity is tending to expanding the high level.Secondlly, synthetic analysis and comparative analysis are used to study the asymmetrical structure about temperature and humidity of different intensity change of tropical cyclone(TC) intensity over Western North Pacific and South China Sea during 1979-2010 years. The results show that: The specific humidity of RI has weak asymmetry and wavenumber-1 asymmetry is mainly situated in northeast and southwest quadrant. While RW has intense asymmetry and wavenumber-1 asymmetry is mainly located in northwest and southeast quadrant. RI has the double warm-core structure generally which are located in 300 hPa and 800 hPa of high and low level warm-core respectively. Meantime, RI will appear double wet-core structure when the occurrence of RI after 24 hour. While RW shows frontal structure and exists wet-core in 850 hPa. The threshold(0.7K s-1) of difference of temperature gradient(850-200hPa) could judge the occurrence of RI or RW well. 0.7K s-1 and below usually means RI(conversely higher than 0.7K s-1 in favor of the occurrence of RW). The response time of TC intensity on the threshold of difference temperature gradient exists the lag time abouFinally, making use of WRF for numerical simulation of Vicente, through analyzing the model data, we focus on the evolution of temperature and humidity structure and possible reasons in the process of rapid intensification. The results show that: Vicente has obvious double warm heart and double wet heart on vertical structure features in the RI process. Accompanied by high level warm heart growing, low-level warm heart and the high level of wet heart diminishing and disappearing, when Vicente reaches strongest stage, it shows classic warm-core structure. The 1-wave asymmetrical component of specific humidity at 925 hPa can stimulate the specific humidity in lower troposphere enriching and its upward motion. Mainly because the 1-wave asymmetrical component of specific humidity can cause upward movement, and when the 1-wave asymmetrical component of specific humidity is greater than 2g.kg-1, the vertical motion will tilt.