摘要:为了做好连续回流暴雨的中期与延伸期预报，采用小波分析、Lanczos时间滤波器等方法研究了2019年广东前汛期降水与大气季节内振荡的关系，分析了4～5月发生在西南部的两次连续回流暴雨的平均环流场及其低频传播特征的差异，并与6月广东北部锋面型连续暴雨进行对比分析。结果表明，4～5月两次以阳江为中心的西南部连续暴雨及前汛期降水均具有准23 d振荡，它们分别为有、无明显冷空气影响的连续回流暴雨且对应的大气环流场及低频传播特征具有明显的不同：4月12～14日连续回流暴雨期间，500 hPa中高纬度具有稳定的“西阻”和“东阻”，使冷空气不断地从东海入海高压的南部东移南下，925 hPa形成以阳江为中心相对干冷的强东南风与来自南海中南部从中南半岛转向的暖湿偏南风的辐合渐近线；而5月23～26日连续回流暴雨期间，500 hPa华东—东海—黄海为稳定高压坝，广东长时间处于高原槽前西南气流中，地面上处于东海出海变性高压脊西南部及北部湾西南低槽前，925 hPa形成以阳江为中心来自孟加拉湾的强偏南风与珠江口以东东南风的辐合渐近线。来自我国中部（东海以东）低频反气旋南侧（西南侧）逐渐加强南传的低频东北风（东南风）与从140°E附近的西太平洋西传（孟加拉湾东传）到广东并加强的低频北风（南风）汇合在广东西南部，并有（无）与从南海中北部北传的低频气旋北侧低频东风相遇，导致4月12～14日（5月23～26日）有（无）明显冷空气影响的连续回流暴雨发生。而6月广东北部为东亚深槽引导的冷空气与来自孟加拉强盛西南风交汇所产生的锋面型连续暴雨，来自我国中部、孟加拉湾分别逐渐加强向南、向东传播到达广东的低频西南风，与来自中纬度低频反气旋外围的干冷东北风交汇在江南或南海北部，导致广东北部6月9～13日连续暴雨的发生。
关键词:连续回流暴雨/
环流特征/
传播特征/
季节内振荡
Abstract:In order to make better medium-term and extended-range forecast of continuous backflow rainstorms, wavelet analysis and Lanczos time filter were used to analyze the relationship between daily precipitations and atmospheric intraseasonal oscillations during the first rainy season in Guangdong in 2019. The mean circulations of two backflow continuous rainstorms over southwest of Guangdong during April and May and their low-frequency propagation characteristics were analyzed and compared with the frontal-type continuous rainstorms over north of Guangdong during June. The results show that the two continuous backflow rainstorms near Yangjiang from April to May and the precipitation during the first rainy season exhibited a quasi-23-day periodic oscillation. They were continuous backflow rainstorms with or without the influence of cold air, and their corresponding atmospheric circulation fields and low-frequency propagation were significantly different. During the continuous backflow rainstorms on 12–14 April, there were stable “west blocking” and “east blocking” at the middle and high latitudes at 500 hPa, which made cold air continuously moving southeast from the south of the high pressure that was transformed over the East China Sea. The convergence asymptote of relatively dry and cold strong southeast wind and the warm humid southerly wind from the mid-southern South China Sea by Indochina Peninsula was formed near Yangjiang at 925 hPa. During the continuous rainstorms on 23–26 May, there was a stable high-pressure ridge over the regions of eastern China, East China Sea, and Yellow Sea at 500 hPa. Because of such, Guangdong for a long time was under the southwestern airflow coming from the plateau trough, and on the ground was in the southwestern position of the degenerative high-pressure ridge from the East China Sea, in front of the trough from Beibu Bay to the southwest of China. At 925 hPa, the convergence asymptote was formed from the strong southerly winds coming from the Bay of Bengal centered in Yangjiang and the southeast winds coming from the east of the Pearl River Estuary. The low-frequency northeast wind (Southeast wind) from the south (southwest) of low frequency anticyclone in the central China (east of the East China Sea) was gradually strengthened southward, merging at the southwest of Guangdong with the enhanced low-frequency northerly (southerly) winds coming westward from the western Pacific near 140°E (eastward from the Bay of Bengal), which in turn encountered with (without) low-frequency eastern wind from the north of low frequency cyclone propagating northward from the mid-northern South China Sea. This finally resulted in the continuous backflow rainstorms with (without) obvious influence of cold air. But the frontal-type continuous rainstorm during June was affected by convergence between cold air induced by deep East Asian trough and southwesterly from Bengal Bay. The enhanced low-frequency southwesterly propagated southwards and eastwards to Guangdong from mid China and Bengal Bay. It converged with the low-frequency cold dry northeasterly winds from the periphery of the mid-latitude anticyclone at the south of Yangtze River or the north of South China Sea, which led to the happening of the continuous rainstorms during 9–13 June.
Key words:Continuous backflow rainstorm/
Circulation characteristics/
Propagation characteristics/
Intraseasonal oscillation
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