广东6月持续性暴雨期间的大气环流异常

Anomalous atmospheric circulation characteristics of the sustained torrential rainfall over Guangdong in June

中文关键词:  广东持续性暴雨  经向波列  环流异常  前汛期

英文关键词:Sustained torrential rainfall over Guangdong  Meridional wave train  Anomalous circulation  Pre-flooding season

中文摘要:

      利用1979—2011年共33年广东86个观测站日降水和全球大气多要素日平均资料,分析广东前汛期降水异常(包括暴雨和无雨)的环流特征。结果表明,广东6月持续性暴雨和持续性无雨期间大气存在显著的经向遥相关波列,其中,持续性暴雨过程波列更完整,非持续性暴雨(或非持续性无雨)则波列不显著,而4、5月的持续性暴雨或持续性无雨过程都没有波列出现。在经向波列存在的情况下,对流层中高层大气西风带环流经向度增大、槽脊发展增强,中高纬度这种持续稳定的环流形势,有利于冷空气和高空槽影响华南;在高层200 hPa,华南处于偏西风和西南风异常之间的气流辐散区域,有利于高层辐散;对流层中低层西太平洋副热带高压偏强、西脊点偏西,华南上升、南海下沉的垂直异常经圈环流建立;同时对流层低层来源于印度和孟加拉湾北部以及热带太平洋的水汽输送明显加强,从而为持续性暴雨过程提供有利的环流背景以及暴雨区所需的动力和水汽条件,可见经向波列通过对流层高、中、低层大气环流异常影响持续性暴雨。在没有经向波列的情况下,当500 hPa华南地区有西风槽活动、850 hPa南海北部西风偏强,广东局地动力上升条件和水汽输送条件达到一定程度,则只能出现非持续性暴雨。因此,经向波列可为区分持续暴雨与非持续暴雨预报提供参考。与广东降水持续异常相关的经向波列受中高纬度罗斯贝波、热带对流以及中低纬度太平洋地区大气异常等多方面的共同影响。

英文摘要:

      By using the 33-year (1979-2011) 86-station daily precipitation observations of Guangdong Province and the global daily atmospheric data from NCEP-DOE Reanalysis 2, the anomalous circulation characteristics of abnormal rainfall during the pre-flooding season in Guangdong were analyzed. We found whether a torrential rainfall in June would be persistent depends in part on whether there exist an meridional wave train. However, the link between the persistence of severe rainfall and meridional wave train does not exist in April and May. The meridional wave train impacts on the process of the sustained torrential rainfall through changing the atmospheric circulation anomalies at upper, middle and lower levels of the troposphere. Accompanied with an meridional wave train, the meridionality of the westerly circulation enhances at upper and middle levels of the troposphere, which is favorable for the invasion of cold air and upper trough. Southern China is in the airflow spread area between anomalous westerly and southwesterly at 200 hPa which is beneficial to divergence at upper levels. The western Pacific subtropical high is stronger and its west ridge is located more westward than normal. The vertical meridional circulation anomaly in which it is rising in southern China and sinking in the South China Sea is set up. Water vapor transport at low levels from both northern India and the Bay of Bengal, as well as from the tropical western Pacific is enhanced at the same time. Therefore, the stable circulation background and both the dynamics ascending and water vapor conditions in local region for sustained torrential rainfall are provided. In the case of absence of meridional wave train, only 1-day or 2-day torrential rainfall may happen when the trough at 500 hPa is active in southern China, the westerly at 850 hPa is intensive in the northern region of the South China Sea, and dynamical ascending and water vapor conditions in local are satisfied to some extent. So the meridional wave trains may be used to distinguish whether the torrential rainfall is sustained or not. The meridional wave trains associated with sustained anomaly of rainfall in Guangdong are affected by the Rosssby wave from the middle and high latitudes, tropical convection as well as the atmospheric anomaly from the middle and low latitudes in the Pacific.