Analysis Of Variability Of Soil Moisture Over Hetao Regions And Its Effect On Short-term Climate

Soil moisture data between 1981-2002 were used for diagnostic analysis to explore its variability and its effect on climate in this paper.Main contents were concluded as following:(1) Basic characteristic analysis of soil moisture: vertical and horizontal distribution characteristics were analyzed and characteristics of seasonal, annual and interannual variability were analyzed either. It is found that vertical distribution of local soil moisture varied seasonally. During spring, the upper level is wet and lower level is dry. However, when the rainy season comes, the upper level gets wet quickly and it is wetter than lower level. The local soil moisture exists with 5-6 year cycle and quasi 2.5 year cycle. In general, it tends to drop down. There exists an abrupt change in 1991 that before the year its interannual variability is bigger but after that it's smaller.(2) Analysis of soil moisture and climate factors of Hetao regions during drought and flood years: in situ station data were used for analysis. It is found that variability of soil moisture and evaporation over Hetao regions ( around the middle reach of the Yellow River ) is out of phase, but rainfalls and atmospheric relative humidity is in phase. In the beginning of spring, increase of evaporation of soil is the reason of lack of moisture of soil. Increase of rainfalls is the leading factors of increase of moisture of soil. Analysis of soil moisture of Hetao regions during drought and flood years show that variability of soil moisture of the mid-south Hetao regions is a sensitive factor of variability of climate over north China. During dry year, Hetao regions are easily controlled by northly flow;during wet year, westerly and southly flow join over the regions, which reveal the essentiality of land - air reciprocity.(3) Correlation between soil moisture over mid-south Hetao regions and other elements: Correlation between soil moisture over mid-south Hetao regions and geopotential height shows that significant correlation regions are located in regionswhere the relatively steady stationary wave exists;delay correlation analysis show that change of soil moisture could cause change of geopotential height, and further cause change of location and intensity of the stationary wave, which leads to change of rainfalls and air temperature. The significant signals could appear at least one month earlier.