渭河流域土壤湿度异常特征与我国若干气候背景的联系

The anomaly characteristics of the soil moisture of Wei River Basin and its contact with several climate background in China

利用中国1981—2007年土壤湿度资料、地面气象观测旬资料及东亚夏季风强度指数、NCEPⅡ再分析资料,通过诊断分析探讨了土壤湿度变化的敏感区——渭河流域土壤湿度异常与我国若干气候背景的联系。合成分析显示,渭河流域土壤湿度异常干年,中国北方中东部大部分地区土壤偏干,降水量偏少,蒸发皿蒸发偏强,空气相对湿度偏小,湿年反之;大气环流也呈完全相反的形势,干年亚洲中高纬位势高度距平分布西正东负,湿年反之。滞后相关分析表明,土壤湿度的变化可引起500 h Pa大气高度场的变化,从而使定常波的位置和强度发生变化,进而导致降水场的变化;渭河流域13—16旬土壤湿度与17—20旬500 h Pa大气环流表现出欧亚—太平洋遥相关(EUP)型,表明土壤湿度对大气的影响可通过大气遥相关的作用传播到其他区域;土壤湿度蒸发对低层大气水汽通量有正贡献,但这种贡献对产生降水所需的水汽而言是次要的,在我国中东部,前期土壤湿度对夏季降水的影响小,对秋季降水则有明显影响;渭河流域前一年秋季和当年春季土壤湿度与东亚夏季风强度指数显著正相关,表明秋季和春季陆面土壤湿度状况对东亚夏季风的强弱有正反馈的作用。

Based on agrometeorological station soil moisture data from 1981 to 2007 in China,along with 10 days of surface meteorological observation data,East Asian summer monsoon intensity index data,and NCEP reanalysis-Ⅱ data,this paper uses diagnostic analysis to discuss the relationship between the soil moisture anomaly of the Wei River Basin（an area sensitive to soil moisture change） and the country＇s climate background,in order to explore the feedback mechanisms of land surface soil moisture to the short-term climate.Composite analysis shows that the soil is drier,the rainfall amount is lower,the pan evaporation is stronger,and the atmospheric relative humidity is smaller,in most parts of central-eastern North China during abnormally dry years of soil moisture in the Wei River Basin.The opposite is the case during abnormally wet years.Atmospheric circulation is also opposite：The anomaly is positive in the west and negative in the east over middle and high latitudes of Asia at the 500 hPa geopotential height during abnormally dry years,but negative in the west and positive in the east during abnormally wet years.Lag correlation analysis shows that a change in soil moisture can cause a change in the 500 hPa atmospheric geopotential height field so the standing wave change in the location and intensity and which led to precipitation field change.The correlation coefficients show an atmospheric teleconnection type of Europe-Asia and the Pacific between 13-16 ten days＇ soil moisture of Wei River Basin and 17-20 ten days＇ 500 hPa geopotential height atmospheric circulation that indicate the impact of soil moisture on atmosphere spread to other regions by the atmospheric teleconnection.Soil moisture contributes positively to the low-level atmospheric water vapor flux,but this kind of contribution is secondary for water vapor to produce precipitation.The previous soil moisture＇s influence on summer precipitation is small,but has an obvious impact on autumn precipitation in East China.（3）Soil moistue of Wei River Basin of fall of last year and spring of the year is positive correlated significantly with the east asian summer monsoon index.It valid that the soil moisture conditions of land surface of fall and spring fed back positively to the east asian summer monsoon＇s intensity.At 850 hPa geopotential height,it is east wind anomaly from India Peninsula to the South China Sea in June to August after the soil moisture dry year in autumn and spring of Weihe River basin and it maintain anticyclonic circulation anomaly in South China Sea to the Western Pacific region-such as weak Asian Monsoon.It is contrary in wet years.（4）This paper disscuss preliminarily the relation of the soil moisture of Wei River Basin and several climate background in China by the observation data analysis.If it is positive（negative） in west and negative（positive） in east at middle and high altitudes in Asia in 500 hPa geopotential height anomaly distribution than the rainfall less（more） in most part of central-eastern North China and soil moisture of Wei River Basin is drier（wetter）.Soil moisture anomaly of Wei River Basin＇s drier（wetter） can means the land surface＇s drier（wetter） of the most part of central-eastern North China. Drier（wetter） soil moisture can make the standing wave＇s location and intensity change at the atmosphere geopotential height field through the exchange of energy and moisture in the process of land surface and it can result further the change of precipitation field.The influence of soil dry（wet） exist atmosphere teleconnection in 500 hPa geopotential height.This is in agreement with the results of numerical experiments.Therefore the soil moisture anomaly of Wei River Basin can be tried as a signal of short-term climate prediction in central-eastern China.