Analysis Of Water Vapor Transport Variation In North China Base On Lagrangian Method And Its Impact Factor

Using the NCEP reanalysis data and daily rainfall data of 753 stations from 1951 to 2009, with Eulerian method, local water vapor transport variation during flood season in North China is analysed; With Lagrangian trajectory model (HYSPLIT) developed by NOAA, air parcel trajectory was stimulated during flood season in North China from 1951 to 2009. Combined with huge amounts of gas block tracking method, SEOF and other statistical methods, climate characteristics of water vapor sources, temporal and spatial variation, and their eventual relationship with precipitation in North China, and the contact of SST field and circulation field are analysed in this paper. Major conclusions are as follows:(1) Based on Eulerian method:Local moisture vapor transport during the flood season of North China mainly comes from the south and west channel of water vapor transport, accounting for 60% and 40% of the total input, respectively. The east and the northern channel for water vapor flow out, accounting for 79% and 21% of the total output. Local water vapor balance present weakening process after rising first, and the overall decline which the south channel played a dominant role.(2) Based on Lagrangian method:Climatological trajectory analysis indicate that moisture in North China mainly originates from:Eurasia (14.4%); local region (10.2%); the Bay of Bengal-South China Sea (33.8%); the Indian Ocean (10.7%); and the Pacific (30.9%).(3) A spatio-temporal analysis of moisture trajectory based on the SEOF technique reveals that the spatial distribution is primarily characterized by north-south oriented dipoles. The temporal variation reveals a regime transition after 1980, from south domination to north domination. Precipitation characteristics in North China correlated well with the "north and south seesaw" type of water vapor transmission in decadal time-scale.(4) Quantitative estimation of source:Water vapor source of North China present the north and the south branch. After 1980, the source over the vast sea areas, including MengWan-the South China Sea, the West Pacific, Indian Ocean, pass from a greater to a smaller moisture contribution (from 43.2% to 43.2%), and Eurasia, Local area, Northwest Pacific pass from a smaller to a greater moisture contribution (12.2% to 23.1%). After 1980, The total water vapor sources to reduce 10.8%, corresponding precipitation of 15.8% reduction in North China. The Bay of Bengal, the South China Sea and the Indian Ocean are dominant moisture source areas, reducing 11.8%,5.6%, respectively.(5) Analysis of relationship between change of water vapor source and the Pacific SST, and the East Asian atmospheric circulation in inter-decadal time scale indicate:for SST field:prior to 1980, PDO in cooling phase, corresponding to a decadal increase for the water vapor sources, while the PDO in warm phase, it shows contrary situation. The PDO is key factor affecting flood water vapor sources of North China present the north and south branch. The circulation field:After 1980, for 500 hPa height field, the domination circulation transform from the radial into zonal, the upper trough from Mongolia to the qinghai-tibet plateau abate, which make cyclonic circulation over the North China upstream reduced; In addition, the 500 hpa temperature decrease in Mongolia to the north of qinghai-tibet plateau region, which makes the region of the upper troposphere of geopotential height decreased, leading high altitude jet to south and east Asian monsoons abate, water vapor is hard to reach in North China; On the other hand, makes pressure in the bottom of the troposphere increases, the water vapor convergence weakened.