摘要
利用国家气象信息中心整编的海南岛18个市县测站的日降水资料和美国NCEP/NCAR的再分析资料,分析了1981—2010年海南岛秋汛期降水的异常及其环流特征。研究结果表明:海南岛汛期降水分布形态与华南其他各区存在差异性,双峰结构不明显,随着暴雨级别的提高,暴雨日分布形态的单峰现象愈加显著,峰值出现在秋汛期内。秋汛期降水在时间分布上存在差异性,尤其是10月上半月内,不同级别的降水逐候分布均出现了急剧变化。在空间分布上也存在显著差异,降水高值区出现在海南岛中-东部,整体均呈一致的自东向西逐渐减弱的分布态势。9月中旬后,华南至南海北部地区处冬夏季风交替时期,天气尺度冷暖系统交汇激烈,高低空天气系统的有利配置导致区域性强降水频频出现在这一时期。其中,南海北部低空风场的走向和风速的差异,及南亚高压的位置变化是10月上半月内降水出现急剧变化的主要原因。低空偏东强风带在南海北部的出现和逐候加强是秋汛期内最显著的环流特征。多个极端降水个例的环流分析也显示,强劲的低空急流是秋汛期特大暴雨的天气学特征中最显著的强信号,急流的存在为暴雨过程提供了充沛的水汽输入和辐合抬升条件,是触发秋汛期极端降水的关键原因。秋汛期南海地区的水汽输送通量值随季节的推进经历了偏南单中心-南北双中心-偏北单中心的演变。输送水汽的气流来自印度洋的西南季风支流,澳大利亚-印尼一带的偏南越赤道气流,大陆冷高压东南侧的东北气流和副高南侧的偏东气流。此外研究结果还表明,特大暴雨发生期间,南亚高压的主体多位于南海北部,相对气候平均态而言,东亚西风槽偏强,副高偏北偏强,偏东低空急流强劲,造成暴雨增幅的水汽主要来自大陆冷高压东南侧的东北气流,副高南侧的偏东气流和印度洋的西南季风支流的输送。
Daily precipitation data, observed by 18 stations in Hainan and compiled by China＇s National Meteor- ological Information Center and NCEP/NCAR reanalysis data from 1971 to 2010, are used to analyze the rainfall anomaly and the climatic characteristics during the autumnal flood season in Hainan. Its association with the at- mospheric circulations is also investigated. The results show that there is significant difference between Hainan and other areas in South China in the rainfall distribution characteristics during the flood season. The evolution of daily rainfall during the flood season in Hainan shows a feature of sing/e-peak rather than double-peak, which becomes more obvious with the intensification of the rainfall magnitude, and the peak appears specifically during the autumnal flood season. During the autumnal flood season, especially in early October, there is dramatic var- iation in rainfall in each pentad and clear homogeneity in both spatial and temporal distribution of rainfall. Large rainfall occurs in the middle and east part of Hainan Island and the intensity gets weaker from east to west. After mid-September, South China and the northern part of South China Sea are subjected to alternating East Asia winter and summer monsoons. There is dramatic interaction between cold and warm synoptic weather systems, which is favorable for the frequent occurrence of heavy rainfall. The main reason for the dramatic variation of the rainfall in early October lies in the rapid change in low-level wind direction and velocity in the southern part of the South China Sea and the position of the East Asia High. The appearance and intensification of the low-level easterly belt in the northern part of the South China Sea are the most distinguishing circulation features for the Autumnal flood season in Hainan. Many extreme rainfall events confirm that strong low-level jets, which bring about plenty of moisture and lead to convergence and uplifting, are the strongest signal for autumnal flood season torrential rain. The low-level jet is converged by four flows, namely, a branch from Indian summer monsoon, a southerly cross-equatorial flow from Australia and Indonesia, a northeasterly flow from the southeast side of the continental cold high and an easterly flow from the south side of the Western Pacific Subtropical High. And the distribution of moisture flux evolves with time, first with a single center in the south, then double centers in the north and south respectively, and finally a single center in the north. Moreover, the study result demonstrates that the main body of the East Asia High is usually located in the north part of South China Sea during extremely torrential rain events. The east Asia trough, west Pacific Subtropical High and low-level easterly are much stron- ger than the climatic mean, and the West Pacific Subtropical High tends to lie in the north of its usual position. The moisture contributing to the rainfall amplification is mainly brought about by the northeasterly flow from the south side of the continental cold high, the easterly flow from the south side of the Western Pacific Subtropical High and the Indian summer monsoon.
出处
《热带气象学报》
CSCD
北大核心
2016年第4期533-545,共13页
Journal of Tropical Meteorology
基金
国家自然科学基金项目(41365004)
海南省自然科学基金项目(413132)
公益性行业科研专项(GYHY201306009)共同资助
关键词
海南岛秋汛期
降水
大尺度环流
偏东低空急流
水汽输送
autumnal flood season
rainfall
large-scale circulation
low-level easterly jet
water vapor transport
