春季天气变率对华北沙尘暴频次的影响

利用欧洲中期数值天气预报中心再分析资料及地面台站观测资料,分析华北春季沙尘暴日数与500 hPa月平均环流及与近地面环流天气变率长期变化的关系,分析时段为1962~2000年。研究发现华北地区春季沙尘暴频次与东亚地区中高纬度500 hPa高度场有显著的负相关,相关中心区在蒙古国及西伯利亚一带,这可能说明高空环流场在这种形势下易于造成高纬度冷空气南下,因此使得华北沙尘暴频次增加。天气过程是形成沙尘暴的直接原因,东亚地区天气变率存在明显的年际和长期变化,研究发现天气变率与沙尘暴频次之间有非常显著的关系：当天气尺度变率增大 (减少) 时,沙尘暴频次也增加 (减少)。其中具体分析了850 hPa低压和地面冷高压活动与沙尘暴的关系,发现东北低压及自蒙古和西伯利亚南下的冷空气活动都对华北沙尘暴频次有明显的影响。近40年来东亚天气变率有显著的减弱趋势,这也在很大程度上解释了沙尘暴频数的显著减少。另外,北极涛动对东亚天气变率和华北沙尘暴频次的年际变化也有一定的影响,北极涛动强的年份华北沙尘暴次数偏少。

Influences of Synoptic Variability on Spring Sand Storm Frequency in North China

Based on the European Center for Medium-Range Weather Forecasts reanalysis datasets and the observed data for dust storms in North China, the authors investigated the relationships between dust storm frequency, monthly mean geopotential heights and synoptic variance in middle to lower troposphere for the period 1962 to 2000. The result shows that there is significant negative correlation between spring dust storm frequency and mean 500 hPa geopotential heights in mid-high latitude of East Asia, with correlation centers appearing in the Mongolia and Siberia. That suggests that this particular circulation pattern is likely to cause more cold air activities originating from the high latitudes and consequently result in frequent dust storms in North China. Weather process is the main reason for dust storm. The synoptic variance in East Asia shows evident year-to-year variations and long-term trends. There is significant relationship between synoptic variance and dust storm frequency. Their temporal changes are in phase. In addition, dust storm frequency is strongly correlated with the cyclone frequency (defined as the extremely low 850 hPa heights below the 10 percentiles) and the surface cold highs. It was found that the Northeast Low and cold surge activities of Mongolia and Siberia exert notable influence on dust storm frequency. Synoptic variance in East Asia shows a remarkable decreasing trend in 1962-2000 that explains a large portion of the decreasing in dust storm frequency. In addition, Arctic Oscillation may, in part, play a role in influencing the interannual variations of the synoptic variance and dust storm activities.