华东高温期的大气环流特征分析

CHARACTERISTICS OF ATMOSPHERIC CIRCULATION IN ASSOCIATION WITH HIGH TEMPERATURE OVER EAST CHINA

利用NCEP/NCAR再分析资料和地面气象站点资料,对1951—2005年华东高温日数较多(少)月和高温过程各阶段的500hPa位势高度、850hPa温度和相对湿度及700hPa垂直速度的环流特征进行对比分析。结果表明:在高温日数较多月,副高西伸,850hPa温度较高而相对湿度较低,华东中南部下沉气流明显,华东多为位势高度、温度和垂直速度正距平及相对湿度负距平;而在高温日数较少月,副高东退,850hPa温度较低而相对湿度较高,整个华东为上升气流,并为位势高度、温度和垂直速度负距平及相对湿度正距平。与高温前期和衰退期相比,高温盛期副高北抬西进,华东850hPa温度较高而相对湿度较低,华东南部下沉气流强盛,各要素距平值增加,多数要素距平中心移向华东或其周边。高温间断期则比盛期各要素距平减弱。大气环流要素场及其距平场的变动可以作为预报华东7—8月高温日数多寡和高温进程的参考依据。

Based on the NCEP/NCAR reanalyzed monthly and dally average data and daily maximum temperatures in surface weather stations of East China from 1951 to 2005, the characteristics of atmospheric circulation, including mean geopotential height fields at 500 hPa, mean temperature and relative humidity fields at 850 hPa, and mean vertical velocity fields at 700 hPa, are analyzed for the months with varying number of high temperature days and in four typical phases of high temperature processes. The results indicate that in the months with more high temperature days, West Pacific Subtropical High （WPSH） extends westward, temperature is higher and relative humidity is lower at 850 hPa over East China, and an obvious downdraft occurs over the central and southern parts of East China. The geopotential height, temperature and vertical velocity are positively anomalous, and the relative humidity is negatively anomalous over most parts of East China. In the months with less high temperature days, however, WPSH withdraws eastward, temperature is lower while relative humidity is higher at 850 hPa, and the updraft occurs over the whole region of East China. The geopotential height, temperature and vertical velocity are negatively anomalous and the relative humidity is positively anomalous. Compared with the early and decaying stages of high temperature spans, the prime stage is marked with higher 850 hPa temperature and lower 850 hPa relative humidity over East China, westward- and northward- extending WPSH, a strong downdraft over southern East China, increased anomaly of the atmospheric circulation field, and the location of anomaly centers of some fields in East China or its neighboring regions. The anomaly of the atmospheric circulation field weakens in the break phase of high temperature as compared with that in the other periods. The differences of atmospheric circulation fields and their anomalies could be used as reference for the forecasting of high temperature days and high temperature processes in East China.