欧亚大陆春季植被状况与东亚夏季大气环流的显著联系

The evident linkage of springtime NDVI over Eurasia with East Asian atmospheric circulation in summer

  • 摘要: 地表植被覆盖的变化能通过改变陆面参数,以及生地化循环过程,对区域和全球气候产生重要影响。文中利用1982—2002年欧亚大陆春季归一化植被指数(NDVI)和欧洲中期数值天气预报中心再分析资料,采用奇异值分解分析方法,研究欧亚大陆春季植被状况与东亚夏季大气环流的关系。结果表明,贝加尔湖以西区域(55°—65°N,60°—100°E)春季植被状况与东亚夏季大气环流存在显著联系。当春季该区植被指数偏高时,在对流层高层从巴尔喀什湖、贝加尔湖至日本北部,以及中国华南和中南半岛上空存在显著的纬向风正异常,中国华北地区和江淮地区以北为显著负异常,异常中心自北向南依次为“正-负-正”分布,说明东亚夏季200 hPa西风急流轴偏南;相应的在对流层中层15°—25°N地区西风偏强,伴随偏强上升气流,而在25°—42°N地区西风偏弱,并且在32°N附近存在显著下沉气流;在对流层低层,中国江淮流域以北、华北及贝加尔湖以东地区存在明显的反气旋型风场异常,而华南存在东北风异常。这种环流特征说明东亚夏季风偏弱,雨带偏南,并且使得中国华南降水偏多,华南以北大部分地区降水偏少,同时中国东南以及青藏高原东南部温度偏低,而中国北方以及江淮流域温度偏高。欧亚大陆春季植被状况与东亚夏季风的显著关系为东亚夏季风预测提供了有用的帮助。

     

    Abstract: Vegetation can feedback on climate, both directly on the energy budget through surface albedo and exchanges of heat, water, and momentum and indirectly on the biogeochemical process. The purpose of this paper is to provide the statistical linkage of springtime vegetation variations over the Eurasia with summer East Asian atmospheric circulation using observational data. We firstly apply the European Center for MediumRange Weather Forecasts reanalysis data sets (ERA40) and the UMD GLCF GIMMS Normalized Difference Vegetation Index(NDVI) dataset from 1982 to 2002 to reveal the association of the NDVI over Eurasia with the zonal wind at 200 hPa level (U 200) over East Asia using singular value decomposition (SVD) analysis. The results show that there is a significant relation between the spring NDVI in the sensitive area (55°-65°N,60°-100°E) west of Baikal Lake and summer East Asian atmospheric circulation, and the most important NDVI U 200 connection accounts for 33.39% of the total squared covariance. When the spring NDVI in the sensitive area is above the normal, there are remarkable positive zonal wind anomalies in summer in upper troposphere over the Balchas Lake Baikal Lake northern Japan area, and over South China and the Indo China Peninsula, and distinctive negative zonal wind anomalies over North China and the ChangjiangHuaihe River Valley, and therefore the anomalous centers exhibit a positivenegativepositive sign distribution from north to south, which indicate that the summer 200 hPa westerly axis lies south of the normal position. In middle troposphere, the westerly is stronger between 15°N and 25°N accompanied with a stronger ascending motion, but weaker between 25°N and 42°N with a distinctive descending motion over about 32°N. In lower troposphere, there are evident anomalous anticyclonic wind anomalies over the Changjiang Huaihe River Valley, North China and the area east of Baikal Lake, and anomalous northeasterly anomalies over South China. Those circulation characters suggest that the East Asian summer monsoon (EASM) is weaker than normal, and the summer rainband lies south of the normal position, which result in excessive summer rainfall in South China and deficit rainfall in the most areas north of South China. Correspondingly, summer temperature is lower than normal over southeast China and the southeastern Tibet Plateau, and higher over northern China and the Changjiang Huaihe River Valley. The possible association between the NDVI over the Eurasian continent and the EASM could provide some help for forecast of EASM.

     

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