近40年东亚季风变化特征及其与海陆温差关系

Variations of East Asian Monsoon and Its Relationships with Land-sea Temperature Difference in Recent 40 Years

利用NCEP/NCAR再分析资料,计算了乔云亭等定义的1957—2000年东亚季风指数,研究了各指数之间相互关系和年际变化的主要特征,在此基础上又利用全国194站1957—2000年地面资料分析东亚季风指数的年际变化与各气象要素场的年际变化之间的关系以及我国近40年气候变化特点。结果表明:西南季风、东南季风和偏北季风的年变化有所差异;夏季,东部地区降水量与相对应各个海区海陆温差负相关显著,并且江淮区对应的海陆温差与东北区和华北区夏季降水有较好的正相关关系,当江淮区对应的海陆温差降低时,江淮区夏季降水量增加,华北区和东北区夏季降水量减少;经过前后两段时期(1957—1978年和1979—2000年)对比发现海陆温差变化对我国季风区夏季降水的影响在增强。同时,发现850hPa气温变化在前后两段时期也发生了显著变化,1979年之前我国东部升温最快的区域位于华北西南部和江淮东部,1979年之后升温最快的区域转移到江淮西部和我国东南部的海面上。

Using the NCEP/NCAR reanalysis grid data for the period of 1957--2000, East Asian Monsoon indexes defined by Qiao Yunting are calculated with interrelationship and annual changes of the indexes are examined. Relationships between the indexes and the variability of the weather elements and characteristics of the climate change in the east of China are analyzed by using surface data from 194 surface stations. The results show that the changes of the southwest monsoon, the southeast monsoon and the north monsoon are different. The intensity of southwest monsoon has been weakening until 1990s as well as the area＇s change. The southeast monsoon becomes weaker in recent 40 years. On the contrary, its range increases. The north monsoon changes little both in the intensity and area in winter. However the summer monsoon affecting the China continent weakens in liner changes in recent 40 years. In summer, the precipitation of Yangtze-Huaihe River valley increases apparently and decreases over the other east parts of China in summer. The precipitation of every part in monsoon region and its corresponding land-sea temperature difference show negative correlation, and the precipitation of Northeast China and North China have positive correlation with the land-sea temperature difference of Yangtze-Huaihe River valley. It means that when the land-sea temperature difference of Yangtze-Huaihe River valley drops, the precipitation of Yangtze-Huaihe River valley increases and that of Northeast China and North China decreases The relationship between land-sea temperature difference and precipitation in two different phases are examined and it is found that the influence of land-sea temperature difference on precipitation in summer enhances in the second phase （1979--2000） than in the first phase （1957--1978）. The temperatures of the east part of China continent and the corresponding sea increase in recent 40 years, and the increasing velocity of the sea is larger than that of the continent, which resulting in the land-sea temperature difference decreasing year by year. That may be the cause why the summer monsoon changes weakly. During the period from 1957 to 1978, the temperatures of 850 hPa in summer drop over the middle and west part of China except north part of Xinjiang and rise over the east of China. During the second period from 1979 to 2000, the temperature of 850 hPa in summer rises all over China except middle and north part of Xingjiang and Qinghai, the north part of Gansu and west part of Inner Mongolia. The area where temperature of 850 hPa in summer increases most greatly moves from southwest of Northern China and east part of Yangtze-Huaihe River valley to west part of Yangtze-Huaihe River valley and the southeast sea to China continent.