我国高空风速的气候学特征

利用全国119个探空站1980~2006年13个等压面和地面附近的月平均风速资料,分析了不同高度年、季节平均风速的气候学特征。结果表明,全国平均200hPa以下风速随高度增加而增加,200hPa~30hPa之间风速随高度增加而降低,30hPa以上风速随高度增加而再呈增加趋势;春、秋季平均风速随高度变化与年平均相似,但冬、夏季的垂直分布差异明显;700hPa及其以上最大风速出现在1月,最小风速在7月或8月;850hPa和地面最大风速发生在4月;对流层风速年较差从下向上增加,在200hPa附近风速年较差最大。我国地面风速在东、西部地区较大,中部地区较小;500hPa年平均风速分布呈西低东高态势,最大中心出现在辽东半岛东部;200hPa年平均风速在江淮地区出现高值中心;500hPa冬季最大风速区在大陆南部,夏季北移并向西扩展;200hPa各季强风速区基本呈东西走向的带状分布,其中春季在江淮地区,夏季移至西北,秋季位于黄淮地区,冬季位置最南。

Climatology of upper wind speeds over China

The annual and seasonal mean wind speeds of upper atmosphere in the period 1980~2006 over China are analyzed for 13 heights (850 hPa, 700 hPa, 500 hPa, 400 hPa, 300 hPa, 250 hPa, 200 hPa, 150 hPa, 100 hPa, 70 hPa, 50 hPa, 30 hPa, 20 hPa) and surface using the radio sounding data from 119 stations. The data are well distributed across the country, and they are standardized before the analysis. The result of our study presents a clear temporal and spatial pattern of mean wind speeds. The country-averaged annual and seasonal mean wind speeds usually increase with height up to 200 hPa, where they reach the maximum. Wind speeds then drop with height between 200~30 hPa, and they again increase above 30 hPa. Mean wind speeds of spring and autumn months bear more similar vertical change with annual mean wind speeds, while winter and summer see a marked contrast, with the winter mean wind speeds at various heights especially above 500 hPa being significantly larger than those of summertime. Generally speaking, mean wind speeds and the yearly range obviously increase from the surface to 200 hPa where subtropical westerly jet stream core is located. The horizontal distribution features of mean wind speeds are also generalized. The surface annual wind speeds are usually larger in western and eastern coastal regions, and smaller in central parts of China; Higher annual mean wind speeds at 500 hPa are observed in eastern China, with the maximum wind speeds spot over the Liaodong Peninsula of Northeast China, and lower wind speeds at this height go over the Tibetan Plateau; Annual mean maximum wind speeds at 200 hPa are between the Yangtze and Huaihe rivers. At the surface, seasonal mean wind speeds have a similar horizontal distribution with annual ones. At 500 hPa, however, the maximum wind speeds for different seasons are obviously distributed in different regions. The belt of maximum wind speeds in wintertime are observed in southern China, while it moves to the north and extends to the west in summertime. Maximum seasonal mean wind speeds at 200 hPa are seen in an east-west belt. The belt is located between the Yangtze and Huaihe rivers in spring months, in southern Xinjiang and western Inner Mongolia in summertime, between the Yellow and Huaihe rivers in autumn, and in southern China in wintertime, which corresponds well to the seasonal movements of subtropical westerly jet stream at the upper troposphere.