华北地区干旱的气候背景及其前兆强信号

CLIMATOLOGICAL BACKGROUND AND PREVIOUS STRONGER SIGNAL OF ANOMALY DROUGHT OVER NORTH CHINA

将华北地区春、夏季出现异常干旱和多雨典型年份的 5 0 0hPa高度和北太平洋海温的距平进行合成 ,讨论了干旱期和多雨期大气环流和海洋变化的气候背景特征。结果表明 ,华北地区的干旱期和多雨期间的大气环流和海温变化存在趋势性差异。以 3个特旱年为例 ,使用信噪比的方法识别发生特别干旱的前期大气、海洋的强信号。虽然 3个特旱年的前期大气和海洋表现出的强信号的位置和强度并不完全一致 ,但是乌拉尔山脉附近和贝加尔湖附近高度的异常变化及黑潮、暖池及Nino

Drought disaster in North China occurs frequently, it is one of the areas in China where drought extended widest, its intensity was most serious and lasting time was longest. In particular, in recent years, the serious drought extremely threatens agriculture, thereby economics, ecology and even daily life of people were impacted. Therefore it is important to find the causes of the persistent drought in North China, and identify the prior signal of drought degree and its lasting time. In this paper, the characteristics of circulation and ocean variation during dry and wet periods over North China are analyzed by using composition anomaly. The inter-decade tendency changes of 500 hPa height and sea surface temperature (SST) in North Pacific have great influence on Continued drought since 1980s. The results show that there were the correlations between the anomaly drought over North China and the tendency changes of westerly circulation and subtropical high. Based on signal-noise ratio the previous stronger signals of 3 severe drought events are discriminated from 500 hPa height field and SST field. The meaning of the stronger signal-noise ratio is that the remarkable difference between the recent atmospheric and oceanic anomaly and the multi-year mean occurred. For example, there were some antecedent strong signals before the summer drought in 1999, such as typical high control pattern in East Asia circulation, long lasting SST increasing abnormally over Kuroshio and Nino 4. Though the location and strength of the stronger signals before occurring of severe drought event are not all the same, the anomaly variations of the height nearby Ural Mountains and Bajkal Lake and the SST nearby Kuroshio, warm pool and Nino 4 region are important previous stronger signals.