Studies On The Change And Causes Of Sand-Dust Weather In North China During Recent Ten Years

Dust strom, mostly appeared in the northwest and northern part in China, constitutes a part of the dust strom process in Central Asia. Dust strom is most likely from deteriorated grasslands, Gobi, alluvial siol, lacustrine sediments and wadis at the outer edge of deserts. By using the station observations of north China and the data from Terra/MODIS of NASA from2002to2011, the characteristics of sand-dust weather in northern China were analyzed. The relationships between sand-dust weather corresponding to other factors, such as strong winds and the surface characteristics, were researched.(1) In this paper, based on the data of meteorological observational and normalized difference vegetation index (NDVI) from2002to2011, the characteristics of sand-dust weather in northern China were analyzed. The relationships between sand-dust weather corresponding to other factors such as strong winds and NDVI were explored.①The results show that the sand-dust weather increased a lot in northern China in the2002and2006compared with the2004-2005,2007-2011. The sand-dust weather and strong winds frequency has good relationship,②The Sand-dust weather and the change of the isoline of NDVI0.2are relational. When the isoline of NDVI0.2eastward advances, the sand-dust weather increases; when it westward retreats, the sand-dust weather decreases.③Sand-dust weather frequency was positively correlated with strong winds near desert regions, the negative correlation between the NDVI and Sand-dust weather frequency was identified in the desert-steppe zone.④If the strong winds frequency increases and NDVI reduces, sand-dust weather in northern China is likely to becomes active.(2) In this paper, based on meteorological data, API data, and the NCEP reanalysis data, the characteristics and the transport of the strong dust storm from19to20March2010were analyzed. The air quality in17key environmental protection cities of northern China was investigated.①The results shows:the strong dust strom was caused by cold air moving east quickly, meanwhile a cold front near the groud which clearly moved east. The reduce of soil moisture in the sand dust source areas provided conditions for sand rising, and by the high speed northwest air stream in the lower atmosphere, the dust from source area was transported to the downstream areas.②API increased quickly in dust influenced areas. On March20. API in Hohhot,Yinchuang,Datong and Beijing was all500, API in Xining,Jinan ang Lanzhou was461,409,328,respectively. The pollution level was V, the air pollution reached a high level during the dust storm.(3) In this paper, based on the data of the Zhurihe meteorological observational and normalized difference vegetation index (NDVI), leaf area index (LAI), net primary productivity (NPP) from2002to2011, the characteristics of sand-dust weather and the relationships between surface conditions and sand-dust weather in zhurihe were analyzed.①The results show that the threshold wind speed of9.4m/s is high in Zhurihe. The frequency of Sand-dust weather and strong winds is fluctuant from2002to2011. Sand-dust weather frequency is positively correlated with strong winds. The worse the surface conditions, the more vulnerable to wind erosion and sand and dust weather are more likely to occur.②The normalized dust outbreak frequency (NfDO) is the ratio of sand-dust weather frequency to strong winds frequency. NfDO for spring was always low in Zhurihe, when the accumulated precipitation amount for June to August,NDVI,LAI and NPP of the maximum for June to August of the previous year exceeded their thresholds (100mm,0.24,0.3and0.6gC/m2/day,respectively).③This suggests that the precipitation amount during the vegetation growing season predominantly controls plant production in summer. Dead leaves of grasses in spring, which are the residues of vegetation from the preceding summer, chiefly control the erodibility in spring and suppress sand-dust outbreaks.