Two different periods of high dust weather frequency in northern China

This study reveals that, during the period 1966-2014, dust weather frequency （DWF） in northern China （north of 30°N） features two high-DWF periods, in 1966-1979 （PI） and 2000-2014 （P2）, when the linear trend of DWF is removed during the study period. Here, DWF denotes the number of days of dust weather events in the spring season （March-April-May）, including dust haze, blowing dust, and dust storms, which occurred in northern China. The results show that the DWF is much higher in PI than in P2, with increased DWF distributed over southern Xinjiang, the central part of northern China. The main cause is the SST difference in the Atlantic and Pacific between the two periods. It is also found that a meridional teleconnection over East Asia in PI and a zonal wave-like pattern over Eurasia in P2 at 200 hPa play a significant role in the interannual variability in the two periods, respectively. SST over the subtropical North Atlantic （extratropical SST between the Norwegian and Barents seas） may partly contribute to the upper-level meridional （zonal） teleconnection in PI （P2）.

近几十年,我国北方春季沙尘的频次的线性趋势下降,但去掉线性趋势后,发现我国北方春季沙尘频次在1966–2014期间有两段沙尘频次的多发年,前一段是1966–1979(P1),后一段是2000–2014(P2)。认识这两段高频沙尘发生的主要特点和可能原因将进一步理解不同年代际背景下沙尘年际变异机理,为沙尘的气候预测提供依据。研究表明前一阶段沙尘的强度是高于后一阶段,沙尘中心分布在南疆和北方中部(华北、河套和内蒙)。主要的原因是北大西洋和北太平洋海温异常不同造成。前者主要受北大西洋副热带海温异常的影响,后者受北大西洋高纬海温异常的影响。前一阶段200 h Pa高层环流出现经向的大气遥相关,导致40–45°N东亚急流加强一方面有利于动量下传造成蒙古气旋活跃,另一方面有利于新疆和蒙古的沙尘输送到我国北方中部区域。后一阶段从北大西洋高纬到东亚呈现纬向波列,导致蒙古气旋南部西风气流加强,沙尘从新疆输送到我国北方。与后一阶段比较,前一阶段的两极冷空气更为活跃,沙尘发生动力条件更强。