江淮地区夏季极端降水分型及其环流异常配置分析
Analysis of Summer Extreme Precipitation Typology and Associated Circulation Anomalies in the Jianghuai Region
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摘要: 提高江淮地区极端降水异常特征和成因认识有助于理解区域气候变化规律,提升防灾减灾能力。本文基于中国地面气象观测站降水数据、NCEP/NCAR再分析资料,采用百分位和Kmeans聚类方法以及大气动力-热力诊断技术,分析了不同类型极端降水事件的环流配置与演变特征。研究表明,根据降水中心落区的差异,江淮极端降水可划分为四种类型,C-Type、N-Type、S-Type与E-Type,前三类集中时段与雨带季节性北跳有关,而第四类较为分散。四种类型极端降水发生期间,降水主要落区位于偏强的南亚高压与西风急流之间的高空辐散区下方,大气垂直速度增大,对流层上中层温度水平梯度加大,中高纬环流经向度较大,副高强度加强,导致来自海洋地区的水汽输送增强。前三种类型与第四类降水在东亚遥相关型(EAP)、低空急流及水汽输送存在差异。前三型对应EAP较显著,存在低空急流,水汽输送主要来自西太平洋和南海,对流层上层气温梯度呈北冷南暖的偶极型异常结构;E-Type型对应的EAP不典型,无明显低空急流,东亚沿海偏东水汽输送明显,对流层上层只存在单极暖中心。分析了四种极端降水热力-动力条件的低频演变,其差异表现为:C-Type型降水发生在副高北抬东退、EAP波列下传期间;N-Type型近地面温度暖中心由长江-黄河之间南移至江南,江淮上空温度上冷下暖;S-Type型发生在副高南移西进过程中,300hPa温度由北冷南暖转为北暖南冷,整层高度场以正值为主;E-Type型发生在副高北抬东退至南移西进过程中,对流旺盛区由低纬加强向中纬移动,200hPa及以下几乎均为温度暖区。进一步分析表明,副高和热力作用的变化对极端降水低频预测具有更好的指示意义。Abstract: Enhancing the understanding of the characteristics and causes of extreme precipitation anomalies in the Jianghuai region is crucial for comprehending regional climate change patterns and improving disaster prevention and mitigation capabilities. Based on gauged precipitation data by China Meteorological Administration and NCEP/NCAR reanalysis data, this study analyzes the circulation configuration and evolutionary characteristics during different types of extreme precipitation events through percentile and K-means clustering methods,atmospheric dynamic-thermodynamic diagnostics technique.. The research indicates that extreme precipitation in the Jianghuai region can be categorized into four types according to the location of precipitation center: C-Type, N-Type, S-Type, and E-Type. The first three types concentrate during periods associated with the seasonal northward shift of the rain belt, while the fourth type is more scattered. During the occurrence of the four types of extreme precipitation, the main precipitation zones are located below the divergence area in the upper troposphere where is between the strong South Asian High and the westerly jet stream, with increased vertical velocity, enhanced temperature gradients in the upper and middle troposphere, greater meridional circulation in mid-high latitudes, intensified subtropical high, and enhanced water vapor transport from oceanic regions. The first three types of precipitation are different from the fourth type in East Asian teleconnection pattern (EAP), low-level jet, and water vapor transport. During the first three types, EAP is more typical, and low-level jet is obvious. The water vapor transport mainly comes from the Western Pacific and South China Sea. The temperature gradient in the upper troposphere is a dipole anomaly structure with colder temperatures to the north and warmer temperatures to the south. When E-type occurs, there is atypical EAP, no obvious low-level jet, obvious easterly water vapor transport along the East Asian coast, and only a unipolar warm center in the upper troposphere. The low-frequency evolution of thermal-dynamic conditions for the four extreme precipitation types differs as follows: C-Type precipitation occurs during the northeastward movement of subtropical high and the downward propagation of the EAP wave train; in the N-type case, the warm center of the near-surface temperature moves southward from the Yangtze-Yellow River to the south of the Yangtze River, and the temperature over the Jianghuai region is cold up and warm down; S-Type occurs during the southwestward movement of subtropical high, with the temperature gradient at 300hPa transitioning from cold north and warm south to warm north and cold south, and positive height values dominating throughout the entire troposphere; E-Type occurs during the northeastward movement followed by the southwestward movement of subtropical high, with convective activity strengthening from low to middle latitudes, and almost entirely warm areas at 200hPa and below. Further analysis demonstrates that changes of subtropical high and thermal effects have better indicative significance for low-frequency prediction of extreme precipitation events.