Modulation of Tropical Precipitation by Shallow and Deep Convective Processes

• Main Authors: Bor-Ting Jong, 鍾博婷
• Other Authors: 周佳
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/48530269385920643934

碩士 === 國立臺灣大學 === 大氣科學研究所 === 101 === Column-integrated moisture and moist static energy (MSE) budgets are used to examine the roles of shallow and deep convective processes in the tropical precipitation. In this study, the gross moist stability (M), usually used for deep convection, is also derived for shallow convection. The roles of shallow and deep convective processes in MSE budget are analyzed by the sign of M. Vertical structure of vertical velocity is decomposed into a shallow-mode, responsible for all boundary layer convergence, and a deep-mode, driven by atmospheric instability. Vertical moisture and MSE advections are used to examine the effects of the shallow- and deep-mode in the tropical hydrological cycle. Also, a multiple linear regression is used to derive M, gross dry stratification (Ms), and gross moisture stratification (Mq) of each mode. The moisture budget shows that the vertical moisture advection of the deep-mode contributes more moisture to precipitation over regions where SSTs are high, while the vertical moisture advection of the shallow-mode supplies moisture over convective regions, with the most over regions where SST gradients are strong. Therefore, shallow-mode plays an important role to supply moisture for precipitation. In the MSE budget, the sign of M determines its role in tropical circulation. M of the shallow-mode (M1) is usually negative, indicating that the circulation associated with the shallow-mode tends to import MSE and destabilizes the atmosphere. On the other hand, M of the deep-mode (M2) is positive, indicating that the circulation associated with the deep-mode tends to export MSE and stabilize the atmosphere. Hence, the shallow-mode, similar with a net-flux term, can be treated as a forcing to free atmosphere. M is mainly controlled by low-level moisture and cloud-top effects. M of the shallow-mode (M1) is negatively related to low-level moisture, while M of the deep-mode (M2) does not have a clear relationship with lower boundary condition, due to a strong cancellation between low-level moisture and cloud-top effects. In this study, the roles of shallow and deep convective processes in the tropics are better understood through both moisture and MSE views. Moreover, the characteristics of M associated with two convective processes are also examined.