Changes of the relationship between spring sand dust frequency and large-scale atmospheric circulation.

Sand / dust occurrences are one of major disasters in arid and semi-arid areas. Understanding its time evolution as well as the impact factors is crucial for policy makers to protect human from health and economic losses. In this paper, we investigate the features of spring sand/dust frequency during 1961–2016 based on 201 surface meteorological stations in northern China, which are divided into four regions as Xinjiang, Northwest China, North China, and Northeast China according to the spatial distribution of sand/dust frequency. Although the regional mean sand/dust frequency exhibits a general declining trend in the last 56 years, it shows fluctuations with the maximum occurrence in the 1970s and the minimum in the 2010s, and abrupt changes can be found in the late 1980s by the Lepage test. We choose 1961–1988 as the active sand/dust period and 1989–2016 as the inactive sand/dust period. Apparent differences are found between these two epochs in the large-scale atmospheric circulations. The geopotential height over Mongolia and Inner Mongolia of China at mid-and lower troposphere became much higher, and the Asian polar vortex weakened and shrank noticeably in the inactive sand/dust period. For 1961–1988, a meridional dipole pattern of significant correlation in heights at mid-and lower levels was dominant over the northeastern Eurasian continent, while for 1989–2016, sand/dust frequency seems to have much closer relationship with local circulation and a zonal dipole structure at lower troposphere dominated over China. The relationship between the 850 hPa vorticity over Mongolia and sand/dust frequency was strengthened after the late 1980s for the western areas, but that was weakened for the eastern areas of northern China. Besides, the intensity of Asian polar vortex at 500 hPa had higher correlation with sand/dust frequency during 1989–2016 particularly for Northwest China. All these findings are important to refine reliable models for short-term climate prediction of sand/dust occurrence in East Asia. • Spring dust frequency decreased generally during 1961–2016 over northern China. • Significant abrupt changes of dust frequency occurred in the late 1980s. • Atmospheric circulation and its relationship with dust frequency differed between 1961 and 1988 and 1989–2016. [ABSTRACT FROM AUTHOR]