Abstract
摘要：降雨量測與預報是重要科學與民生議題。決定降雨的水循環過程包含雲輻射、大氣海陸交換過程與環流的互動。在季風擾動與熱帶氣旋降雨最活躍的東亞暖季，此過程尤其重要。此外根據近三十年來衛星觀測及更長期常規觀測分析結果，伴隨全球暖化強降雨頻率似有增加趨勢。本計劃的總目標在識別並了解東亞與臨近海域內，熱帶雲-降雨與伴隨的水循環過程隨氣候暖化的改變。為達成這個目標，我們提出兩個觀測分析的子計劃以及兩個模擬實驗的子計劃，以及降水趨勢變化的假說：氣候暖化導致強降水與強上升運動發生頻率的增加（亦即降水效率更高），驅動大範圍下沉運動；受到輻射冷卻節制的下沉運動進一步影響較弱的降水。
觀測分析計劃將分析近三十年觀測資料（新一代再分析資料，地面與衛星降雨）。子計劃一將識別全球、東亞與臨近海域內的大尺度水循環特徵，做為本計劃的基礎。子計劃二將分析近幾十年來不同氣候區域內（如海面與陸面）雲-降雨頻譜分佈的趨勢變化。模擬實驗將採取區域氣候模式（RCM）模擬（子計劃三）與水循環過程模式（HCM）模擬（子計劃四）兩個途徑。子計劃三將與中研院周佳合作，分析他進行的兩類組RCM西北太平洋臺風季節模擬實驗：1979-2008事後預報類組以及暖化氣候類組。此RCM模擬場的基態均被spectral nudging方式調整至與控制場一致。子計劃四將採用新一代具備雲模式物理過程的WRF區域模式，進行兩類組實驗。第一類組為2004及2008兩組六月模擬，每組針對該年六月內，每天同一時間為初始場，積分36小時， 共30個實驗。另一類組為當代氣候與暖化氣候兩組模擬。每組針對其六七八月氣候，進行90個36小時實驗。這兩個子計劃模擬結果將與衛星資料比較（模擬量轉至衛星觀測量），並與子計劃二觀測分析結果比較，評估模式水循環過程及其趨勢變化的模擬。綜合觀測與模擬分析的結果，識別各基本變數（溫度，水氣，流場），雲-降雨-上升流的頻譜分佈等隨氣候暖化彼此一致的趨勢變化，本計劃預期將對瞭解與模擬東亞暖季水循環、及其隨全球暖化的變化有突破性的進展。
Abstract: Measuring and predicting rainfall is an important problem both scientifically and practically. The hydrologic processes determining rainfall involve cloud-radiative and surface-atmosphere exchanges processes that are influenced by, and feedbacks onto, circulation. Such interactions are particularly important during the warm season in East Asia where monsoon surges and tropical cyclones are most active events producing heavy rain. Satellite observations since the 1990’s and longer records of conventional observations suggest an increasing risk of heavy rain events with global warming. To properly simulate these heavy rain events and their changes in climate oscillations and global warming environment remains a major challenge to most models in which the hydrologic processes are poorly treated, except some high-resolution models with cloud-resolving model (CRM) physics. However, we have entered a new era for progress with more and new satellite data available and a rapid progress in computer power and advanced models. This project is proposed to use the Weather Research and Forecasting Model (WRF) with the CRM-based physics packages as a core modeling component, and the recent 30-year observations (the new generation reanalysis data NCEP CFS_R and GSFC MERRA, satellite and surface rainfall measurements) to perform the following studies: (1) an observational analysis, (2) model calibration and improvement, and (3) experiments and analysis in comparison with the observed features. In (1), the observed features to be analyzed cover the broad scale low-frequency and regional high-frequency features of hydrologic cycle, and the tendency change in cloud/rainfall distribution from the colder climate in the 1980’s to the warmer climate in the most recent decade. In (2), the model will be prepared to have its mean climate state constrained and its hydrologic cycle evaluated against satellite measurements through a “model to satellite approach”. In (3), two sets of experiments are proposed. The first set is simulation for selected months in the summer of 2004 and 2008. The other set is simulation for warm climate (current decade) and cold climate (1980’s). A particular emphasis is to properly simulate the precipitation features associated with warm season monsoon surges and TCs in East Asia, and to understand their evolution under large-scale forcing and global warming. The WRF simulation results will be compared further with the results by semi-global (tropical channel) WRF and the Goddard MMF all with the same CRM physics package. The proposed research is expected to make a breakthrough in understanding and modeling the hydrologic cycle in East Asian climate oscillations and global warming.
Keyword(s)
雲與降雨
水循環過程
東亞季風
氣候暖化
Clouds and rainfall
Hydrologic process
Asian monsoon
climate change
