宁夏春季沙尘暴频次异常与北太平洋海温异常的关系研究

Correlation between Spring Sandstorm Abnormity in Ningxia and Sea Temperature Abnormity in North Pacific

利用宁夏沙尘暴频次资料、500hPa环流特征量资料、NCEP再分析资料、北太平洋海温场格点资料,采用相关分析、合成分析、小波变换、SVD分析,对宁夏沙尘暴频次与北太平洋海温场的关系进行了研究,探讨了北太平洋海温场通过影响大气环流异常再影响沙尘暴异常的途径。结果表明:宁夏春季沙尘暴频次与前一年10月到当年5月加利福尼亚海温有显著的负相关关系,关键区海温冷、暖异常与宁夏春季沙尘暴日数多、少有较好的时频对应关系;另外发生在北太平洋的厄尔尼诺事件对宁夏春季沙尘暴有重要影响,当北太平洋海温场呈厄尔尼诺(拉尼娜)型分布时,宁夏各地沙尘暴日数以偏少(多)为主。加利福尼亚海温通过影响大气环流,进而影响宁夏沙尘暴的发生,冷水年春季(3—5月),欧亚大陆高空系统较强,环流经向度加大,蒙古气旋加深,有利于极地冷空气南下;从风场形势看,冷水年河套至甘肃、内蒙西部及蒙古国中西部一带高层盛行西北风,而低层多为东南风,这种不稳定形势,也为西北沙尘暴的发生发展创造了有利气候条件。另外,冷水年冬春季东亚大槽位置以偏西为主,极涡强度偏强的年份占优势,西风环流指数负距平的年份偏多,经向环流偏强,冷锋活动频繁,大部分冬季平均气温偏低,表明冬季风偏强的年份为主;而暖水年基本相反。

Based on spring sandstorm observation data in Ningxia, circumfluence characteristic values at 500 hPa, NCEP reanalyzed data, and grid data of sea water temperature in North Pacific, the relationship between the spring sandstorm frequency in Ningxia and sea temperature in North Pacific is analyzed and studied by applying the methods such as correlation analysis, synthetic analysis, wavelet transform and SVD analysis. It is found that there is an obvious negative correlation between the frequency of spring sandstorm in Ningxia and the sea temperature in California from the previous October to May in the same year; The ab- normal cold（or warm） of sea temperature in key region well corresponded to the more（or less）of sandstorms in Ningxia during spring. The E1 Nino events in the North Pacific also affect the spring sandstorm in Ningxia significantly, fewer sandstorms relates with the El Nino pattern, vice versa. In years with colder sea water in California and during spring season in Ningxia, the Eurasian high air systems are stronger, the meridional circulation increases, lower Mongolian cyclones are favorable to guide the cold air to the south and lead to more sandstorms occurrence. Viewed from wind field, the zone from Heitao-Gansu-west Inner Mongolia- midwest Mongolia are dominated by northwest wind at high and by southeast at low, this unstable circumfluence is also advantageous to the development of sandstorms in northwest China. Besides, in colder sea water years, the East Asia troughs mostly locate west, vortex and meridional circulation are stronger, the wester- ly circumfluence indices are more like to be negative, the cold fronts are more dynamic, and most of the years have lower winter temperature. In warmer sea water years, the situations are basically reversed.