Characteristics Of Precipitation And Moisture Transportation In The Pre-Flood Season In South China

Characteristics of spatiotemporal variations in the frontal precipitation period and the summer monsoon precipitation period in South China are studied using daily precipitation data from 76 stations in South China and NCEP reanalysis data. The airflow trajectories during the heavy precipitation in South China in 2008 and the airflow trajectories of different precipitation periods in the pre-flood season in this area have been modeled using Lagrange trajectory model （HYSPLIT₄）. The sources of precipitation and the contributions of different water vapor transportation pathways are also discussed. Results as following:（1）During the frontal precipitation period in South China, there were three important spatial patterns of precipitation, i.e. the consistent pattern in the whole region, the opposite pattern in north and south, the opposite pattern in east and west; the contributions of square error were 51.3%,13.2%,6.6%, accordingly; During the summer monsoon precipitation period in South China, the contributions of square error of the three important spatial patterns are 44.4%,13.6%,6.2%, respectively.（2） The results of modeled airflow trajectories during the heavy precipitation over South China in 2008 showed two major vapor inflow pathways to South China exited. One was southwest airflow, including cross-equatorial vapor transportation from Indian Ocean and southwest vapor transportation from Arabian Sea; one was easterly vapor transportation from south of the western Pacific subtropical high. During the first stage, contribution of southwest airflow accounts for 78% and easterly vapor was 13% of the total transportation; during the second and third stage, the contribution of the southwest airflow decreased, accounting for 59% and 68.6% of the total moisture transportation respectively, while the contribution of easterly vapor increased, being 26.5% and 29.4% of the total moisture transportation respectively; during the fourth stage, the contribution of southwest airflow was 86.5% and the easterly vapor was 7.5% of the total transportation. During the rain period, southwest airflow was the main vapor sources.（3）During the frontal precipitation period, there were two main vapor inflow pathways to South China, having important influences on the anomalies of the frontal precipitation, one was the westerly transportation from Arabian Sea and Bay of Bengal, one was the easterly vapor transportation from south of the western Pacific subtropical high, In wet years of frontal precipitation, water vapor from easterly transportation from the southern of the western Pacific subtropical high was 14% more than that in dry years, reaching to 69%. In dry years of frontal precipitation, the westerly vapor transport from Arabian Sea and Bay of Bengal was 10% more than that in wet years, reaching to 30%.（4）During summer monsoon precipitation period, two major vapor inflow pathways exited to South China:one was southwest airflow, including cross-equatorial vapor transport from the Indian Ocean and the southwest vapor transport from the Arabian Sea and Bay of Bengal, one was the easterly vapor transportation from southern of the western Pacific subtropical high originated from the western Pacific. Of which, the southwest vapor transport was more important. In wet years of summer monsoon precipitation, the moisture originated from the southwest transport over Indian Ocean, Arabian Sea and Bay of Bengal was 18% more than that in dry years, reaching to 88%; In dry years of summer monsoon precipitation, the transportation of vapor originated from the western Pacific was 15% more than that in wet years, reaching to 22%.