东亚夏季风的年代际变率对中国气候的影响

Interdecadal Variability of East-Asian Summer Monsoon and Its Impact on the Climate of China

利用NCEP的海平面气压(SLP) 资料,按6月～8月10oN～50oN陆(110oE)、海(160oE) 气压差≤-5 hPa的累计值代表夏季风强度。每年的值被1951～2000年50年平均值除作为夏季风指数(SMI)。近50年的SMI序列表明有明显的年代际变化,1970年代中之前强夏季风年(SMI > 1) 占优势,1976年开始均为弱夏季风年(SMI < 1)。同时研究了SMI与中国夏季(6月～8月) 降水量与平均气温的关系。发现夏季风强时中国东部华北多雨,长江少雨,同时长江到淮河气温高,但中国西部在夏季风强时南部多雨,北部少雨,气温为北高南低。夏季风弱时情况相反。同时指出,夏季风的年代际变化还影响到夏季风与中国气候的年际变化关系。

Interdecadal variabilities of East-Asian summer monsoon are studied according to the sum of sea level pressure gradient which is ≤-5 hPa between the land (110 o E) and sea (160 o E) from 10 o N to 50 o N. The sum for each year from 1951 to 2000 is divided by the mean sum averaged for the total 50 years, to form a series of Summer Monsoon Index (SMI). It shows a systematic reduction during the period of 1951-2000. Strong monsoon (SMI ≥1.0) was predominated during the first half of the studied period. SMI was less than 1.0 since 1976. Association of the climate in China to the SMI is examined based on the calculation of correlation coefficients between monthly mean temperatures and precipitations in each of 160 stations covered the whole land area of Chinese territory. It indicates that summer (June to August) precipitation increased in North China and decreased along the lower reaches of the Changjiang River when summer monsoon was stronger than the normal, and vice versa. Summer temperatures were higher along the Huaihe and Changjiang rivers when summer monsoon was stronger than the normal.