The Characteristics Of Precipitation Over The Yangtze River Basin In Spring: Comparison Of Moisture And Temperature

The characteristics of interannual variability of spring precipitation over the middle and lower reaches of the Yangtze River basin are analyzed by using the monthly NCEP-NCAR reanalysis dataset and the observed data at the 160 stations in China. At the same time, a method that compare the cold air and water vapor corresponding to the precipitation is analyzed. The main conclusions are as follows:(1) The spring precipitation over the middle and lower reaches of the Yangtze River basin is above normal while the East Asian trough strong than normal, the East Asian jet stream shifts northward, the position of the western Pacific subtropical high is norther than mean state, which can help bring warm and moist airs to the Yangtze River basin. The interannual variability of spring precipitation over the middle and lower reaches of the Yangtze River basin and the sea surface temperature anomalies over the equatorial Pacific and southern Indian Ocean have a very tight relationship.(2) The interannual variability of spring precipitation over the middle and lower reaches of the Yangtze River basin and relative humidity have a very tight positive relationship in the whole troposphere. Plenty of water vapor is necessary for rainfall, and temperature has played an important role in strengthening or weakening the rainfall. In the lower troposphere, more precipitation corresponds to larger water vapor but lower temperature. In the upper troposphere, higher temperature is not benefit for rainfall, but larger water vapor can make air saturated.(3) During the 2011 spring drought, the middle and lower reaches of the Yangtze River basin is controlled by dry and cold air. Though cold air can be brought to the basin and the temperature over the basin is lower than normal, the moisture there is much less than normal, which finally causes the severe drought.