气候变暖背景下祁连山区春季积雨云变化特征

Characteristics of the changes of springtime cumulonimbus (Cb) clouds in Qilian Mt. Region under the background of global warming

利用祁连山区及其周边26个气象观测站1961-2005年春季云形状和气温观测资料,采用线性趋势分析、小波分析等方法,分析了祁连山区春季积雨云出现频率的空间分布与时间变化特征,探讨了与气候变暖的关系,并选用同期NCEP/NCAR全球再分析资料,对祁连山区春季积雨云的环流特征进行分析。结果表明：①祁连山区春季积雨云出现频率在20%~24%,为河西走廊和柴达木盆地的3~6倍,山区东、南侧多于西、北侧,与该区大气水汽含量分布呈现相一致。②近45年来,祁连山区春季平均气温增温0.9℃,气温变化经历了低—高—低—高的4个变化阶段,气温变化的倾向率为0.18℃/10a。③近45年来,祁连山区春季积雨云出现频率与同期气温变化反相,经历了多—少—多—少4个变化阶段,总体呈弱的减少趋势,倾向率为0.2%/10a。④在25a时间尺度上,祁连山区春季气温和积雨云出现频率为反相位变化结构为主,表明在长期气候变化上,气温偏低时期对应积雨云出现偏多时期,气温偏高时期对应积雨云出现偏少时期。⑤祁连山区春季积雨云偏多与偏少年在欧亚500 hPa环流场上存在明显的差异,积雨云出现频次的多少是对欧亚500 hPa环流异常的响应。

Based on meteorological data of springtime cloud shape and surface air temperature at 26 meteorologi- cal stations during 1961-2005 in Qilian Mountain and the surrounding areas, using linear regression analysis and wavelet analysis, the characteristics of temporal variation and spatial distribution of the frequency of Springtime Cb clouds and its relationship with climatic warming are analyzed. The NCEP/NCAR global reanalysis data in the corresponding period are selected for the analysis of the circulation of Springtime Cb clouds in Qilian Mt. Re- gion. The results indicate that： （1） The frequency of springtime Cb clouds in Qilian Mt. Region is obviously high- er than that in Hexi corridor and Qaidam basin. （2） The springtime mean air temperature in Qilian Mt. Region in- creased 0.9 ~ with an increase rate of 0.18 ~C/10a over the recent 45 years, and the increase tendency has become clearer since the 1990s. （3） The frequency of springtime Cb clouds in Qilian Mt. Region decreased weakly over the recent 45 years, and the decreased tendency has become clearer since the 1990s. （4） In the time scale of 25 years, the frequency of springtime Cb clouds and the springtime mean air temperature showed a pattern of an- ti-phase variation mainly in Qilian Mr. Region. However, in the time scale of 6 years with the strongest air tem- perature surge, the frequency of springtime Cb clouds and the spring mean air temperature showed a pattern of in-phase variation. （5） There was a significant difference in the 500 hPa atmospheric circulation between the years with abundant springtime Cb clouds and the years with scarce springtime Cb clouds in Qilian Mt. Region, and the frequency of springtime Cb clouds in Qilian Mt. Region changed in response to the anomaly of 500 hPa circulation in the Eurasian areas. In abundant years, with the Eastern Asia deep trough relatively weaker and the Ural high pressure ridge relatively stronger than in other years, guided by the north-northwest airflow on the front side of the ridge, Polar Cold Air moved to the northwestern China through a northwest path; the low-value sys- tems from Central Asia continuously developed and moved to Qinghai-Tibet Plateau. At the same time, move- ment of the warm and wet airflow from the South China Sea and the East China Sea toward the inland areas strengthened remarkably, and it collided with the cold air from the northern Plateau. More frequent convergences of strengthening warm and cold airflows caused the increase of the frequency of springtime Cb clouds in Qilian Mt. Region. In scarce years, warm anticyclones from West Siberia to Qinghai-Tibet Plateau abnormally strength- ened, and the Eastern Asia deep Trough is relatively stronger than in other years. The path of cold airflow leaned to the east; the regions from Asian continent to western Pacific showed significant winter monsoon characteris- tics. Northwest wind strengthened and blocked the movement of warm and wet airflow from the Southeast to the Northwest of China. Less frequent collisions of the warm and cold airflows in Qilian Mt. Region caused the de- crease of the frequency of springtime Cb clouds in the region.