PRELIMINARY RESEARCH ON EFFECT FACTORS OF BLOWING-SAND WEATHER IN SPRING IN MID-REACHES OF THE HUANGHE RIVER

Study is undertaken of cold air activities and soil moistures effected on the during blowing-sand frequency (referred as BSF hereinafter) in terms of nationwide blowing-sand frequency during 1961 2001, 61 stations soil moisture during 1980 2001, 14:00 (BT) wind speed of 27 stations in Mid-Reaches of the Huanghe River during 1961-2000, nationwide 600 stations daily temperature during 1960-2000, cold air activities (referred as CAA hereinafter) which affected the north China in spring during 1961 2000. Evidence shows that the cold air activities make for outbreaks of blowing-sand in spring, and also lower soil moistures result in outbreaks of blowing-sand. Mid-reaches of the Huanghe River (referred as MRHR hereinafter) locate in the northwest route of cold air outbreaks, the outbreaks along this route cause dust storms in spring frequently. Results suggest that lower tem-perature, higher BSF in spring, i.e., air temperature is one of factors in favor of the blowing-sand out breaks. Yanchi is one station in the target region, its meteorological elements are in highly relationship with the other target stations. In spring, 59 strong cold air activities in north China result in 51 blowing-sand out breaks in Yanchi. Curves of BSF of MRHR and CAA in the north China indicate that the former with high amplitude has the same tendency of CAA, less CAA during 1980s and 1990s is one cause in decrease of BSF in spring. High wind speed is one signature of CAA, which mainly contributes to blowing-sand outbreaks. It is well known that the land surface is much important to blowing-sand out breaks. MRHR belongs to mid-latit ude arid/ sem-i arid area, lower soil moisture in spring due to the less precipitation and less vegetat ion. Out come indicates that higher BSF is in relation with the lower moisture, as well as the thicker dry soil depth which is in favor of blowing-sand outbreaks. In general, frequent cold air activities and lower soil moisture in spring exert notable impacts on high blowing-sand frequency in MRHR.