茂名近海、近岸及陆地站点气象要素对比分析

基于广东省茂名近海海洋浮标站、近岸海上平台站以及陆地电白基准站1年的观测数据,对比分析了风速、风向、温度和湿度的变化特征。(1)三个站点全年的主导风向均呈双峰状,只是主导风向有差异,海洋浮标站和海上平台站以东北风为主,偏南风为辅;而电白基准站主要是东北风和东南风。三个站点的月平均风速最小值都是在8月;最大值海洋浮标站出现在1月,海上平台站为11月,而电白基准站为4月。(2)电白基准站和海上平台站温度年平均日变化呈现出“一谷一峰”型特征;海上浮标站早上有一个低谷,但是峰值不太明显。三个站点月平均温度都是上半年呈上升趋势,下半年呈下降趋势。海洋浮标站纬度更南,受到陆地影响最小,全年高温持续时间最长。(3)三个站点的湿度年平均日变化都是呈“一峰一谷”型,即早晚湿度高,中午到下午低。从日变化振幅上看,电白基准站最大,海上平台站次之,海洋浮标站最小。三个站点湿度月平均都是2—8月湿度较大,最低月份出现在东北季风盛行的11—12月。海洋浮标站出现高湿度的月份最长;海上平台站因为受到陆地的影响,在中午和下午会出现较明显的低值区域。(4)受下垫面的影响,三个站点的风速、温度和湿度的日较差全年平均值,最...     

INTERANNUAL VARIABILITY OF WINTER-TO-SPRING CIRCULATION TRANSITION OVER SOUTHERN CHINA AND ITS SURROUNDING AREAS AND MECHANISMS

The climatological features and interannual variation of winter-to-spring transition over southern China and its surrounding areas, and its possible mechanisms are examined in this study. The climatological mean winter-to-spring transition is approximately in mid-March over southern China and the northern South China Sea. During the transition stage, anomalous southwest winds prevail at low-level over southern China and its nearby regions with enhanced convergence center over southern China, bringing more moisture from the Bay of Bengal (BOB) and the South China Sea (SCS) to southern China; meanwhile, the upper level is characterized by an obvious divergence wind pattern over southern China to the southwest part of Japan and enhanced upward motion. All the change of circulation is favorable to an increase of precipitation over southern China after seasonal transition. The winter-to-spring transition is predominantly on the interannual variation over southern China and the northern SCS. Early winter-to-spring transitions may induce more precipitation over southern China in spring, especially in March, while late cases will result in less precipitation. The interannual variability of the winter-to-spring transition and the related large-scale circulation are closely associated with the decaying phase of ENSO events. The warm ENSO events contribute to early winter-to-spring transitions and more precipitation over southern China.     

华南4—5月持续性干旱及其环流背景

用测站降水量资料和NCEP-DOEⅡ再分析资料等,统计分析了华南春季各月降水量逐年变化的相互关系以及华南4—5月持续性干旱对应的大气环流异常特征,初步探讨了与华南4—5月持续性干旱有关的海温异常及其可能的影响机理。华南春季降水量主要变异型为全区一致型,近30年来华南春季降水量在减少,华南4、5月降水量的逐年变化有显著的同相特征。华南春旱主要是由4—5月的降水持续偏少造成的。在华南4—5月持续干旱年,华南附近高低空都存在一个异常的反气旋,并在华南上空造成异常下沉运动;东亚大槽南支偏弱,不利于中高纬度冷空气南下,因而不利于华南降水。在华南4—5月持续干旱年,热带中太平洋的海温正距平可从前一年12月一直持续到当年5月,其影响华南春旱的机制是:由于赤道中太平洋地区海温正距平,导致该区域的异常辐合上升运动,同时通过罗斯贝波的响应在其西侧即西太平洋赤道南、北两侧低空强迫形成气旋性环流异常,在菲律宾东侧的热带西太平洋上空强迫出异常的上升运动,进而使南海北部和华南地区出现异常的下沉运动,导致干旱;在南海及热带西太平洋上空大气低层出现的偏北风异常也使得来源于南海—西太平洋的水汽输送减弱,不利于华南降水。在华南4—5月持续干旱年,4、5月欧亚大陆中高纬度地区也存在一个持续性的西北—东南向的异常环流波列,其对华南干旱的发生也具有显著的影响作用。