Spatial and Temporal Characteristics of Heavy Precipitation Long-Term Changes in Northeast China and Causation Analysis

Based on daily precipitation data from April to September within 45 years(1961-2005),this paper calculates the precipitation concentration degree(PCD) and precipitation concentration period(PCP) of the heavy rainfall,analyzes the temporal and spatial characteristic of heavy precipitation PCD and PCP,finally discusses the impact of PCD and PCP on circulation background features.The results showed that PCD in Northeast China has a very good correlation with heavy precipitation,which is a very good indication for heavy precipitation.The PCD was increased from east to west in spatial distribution.In view of the temporal,the mid-1960s to the early 1980s,we saw a low-value period of the PCD,and after 1991,PCD in Northeast China was mostly concentrated in high-value period.Heavy precipitation PCP had many low-values only in the 1970s.For most parts of Northeast China(except for northwestern part) PCD increased after the 1990s with a frequent increase in high value years while the changes in the northwestern are just opposite.When the PCD tended to be high,low pressure center existed through the region with the occurrence of high pressure center over the sea surface in the east.The existence of intersection of the west-trend air current with the southeast warm-moist air current is observed along with +-+ fluctuations between 40-50 °N latitude.There is a rising vertical velocity center in the east of Northeast China when PCD is high and speed enhanced with the rise of the altitude(below 300 hPa).The water vapor mainly comes from the cold wet air of the Okhotsk Sea water.In Northeast China there is a water vapor flux divergence of the negative anomaly center,and the formation of the abnormal water vapor convergence zone is conducive to the emergence of heavy precipitation.