Spring snow-disappearance timing and its possible influence on temperature fields over central Eurasia
Spring snow-disappearance timing and its possible influence on temperature fields over central Eurasia
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春季消雪时间及其对欧亚大陆中部气温场的可能影响
DOI：
10.2151/jmsj.79.37
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发表时间：
2001
影响因子：
3.1
通讯作者：
W. Morishima
中科院分区：
文献类型：
--
作者：
M. Shinoda;H. Utsugi;W. Morishima
对欧亚大陆春季积雪消失季节的积雪/大气相互作用进行了观测研究。利用前苏联（FSU） 1966 - 1990年的5天平均雪深资料确定了积雪消失时间。FSU地区的气候性降雪在西南3月初消失，东北6月初消失。应用经验正交函数（EOF）分析了积雪消失时间的年际异常。第一模态为大陆模态，具有广泛的同符号载荷；第二模态（EOF2）具有东西偶极子结构的载荷模式。区域重点放在欧亚大陆中部的EOF2负载的西极，因为该地区的春季积雪被发现与印度夏季风表现出显著的相关性。对EOF2相反相位的综合分析表明，无论冬末积雪深度如何，3月和4月向欧亚大陆中部偏南暖空气大尺度平流增强（减弱）最有可能导致早（晚）雪消失。4月中旬，欧亚大陆中部和南部的大面积地表气温异常最大，积雪面积变异性较大。这些温度异常大于500 hPa水平，可能是由于积雪的影响，而温度异常在5月初消失。这表明欧亚大陆中部的积雪异常可能不会通过陆-地-气相互作用对印度夏季风产生直接影响。
An observational study of snow-cover/atmosphere interactions that occur over Eurasia during the spring snow-disappearance season was conducted. Snow-disappearance timing was determined using five-day averaged snow depth data for 1966 to 1990 in the former Soviet Union (FSU). The climatological snow disappeared in the FSU area during early March in the southwest, and later during early June in the northeast. An empirical orthogonal function (EOF) analysis was applied to interannual anomalies of the snow-disappearance timings. The first EOF is the continental mode with widespread loadings of the same sign, the second mode (EOF2) is characterized by a loading pattern with an east-west dipole structure. The regional focus is placed on central Eurasia in the western pole of the EOF2 loadings, since the spring snow-cover for this region is found to exhibit a significant correlation with the Indian summer monsoon. A composite analysis for the opposite phases of EOF2 shows that, regardless of the leading snow depth during the late winter, the enhanced (reduced) large-scale advection of southerly warm upper-air towards central Eurasia during March and April was most likely to cause the earlier (later) snow disappearance. During mid-April, surface air temperature anomalies are largest over a wide area of central Eurasia, which has high variability in snow-cover extent, and south of the area. These temperature anomalies are larger than those at the 500 hPa level, likely due to the effect of the snow-cover, whereas the temperature anomalies disappeared by early May. This suggests that the snow-cover anomalies over central Eurasia may not have a direct effect on the Indian summer monsoon through the land-surface/atmosphere interaction.