(1) Frontier Research Center for Global Change (FRCGC)
(2) Meteorological Research Institute (MRI)
A multi-layer soil model considering soil-water transportation through vapor and liquid phases under the ground surface has been used for estimating heat and water balances in the Tibetan Autonomous Region of the Tibetan Plateau. The input data is derived from routine meteorological observations in the Tibetan region. Calculated results were verified by the observed latent and sensible heat fluxes, soil-water content, long wave and solar radiation fluxes, and soil-water contents from JEXAM and GAME-Tibet intensive observation period (IOP) data. Observations show good or reasonable agreements with calculated results. Calculations were carried out for 14 stations in 1997 and 17 stations in 1998. Datasets of daily and seasonal variations based on 1997 and 1998 have been established; heat and water balances can be judged from such datasets.
Daily and seasonal variations have been estimated in 1997-98. Net radiation fluxes show relatively large values (annual mean 55 - 80 W/m2) over the Plateau where the elevation is above 3000m. Most (80-90%) of the net radiation is accounted for by sensible heat flux due to low precipitation (e.g. 55 mm in Shiquanhe) in western Tibet (west of about 87E ). Latent heat flux accounts for about 30-50% of the net radiation in east Tibet. From west to east, latent heat flux increases gradually and even exceeds the sensible heat flux in the monsoon season. Latent heat flux (evaporation) is also limited by the relatively low surface temperature because of the high elevation, which indicates why the Plateau serves as the source of several large rivers despite its not so large precipitation. Relatively larger net radiation accompanied with limited evaporation suggests that the Tibetan Plateau plays a role in heating the atmosphere.
Calculations have also been conducted for a climatic representative location, Lhasa, from 1979 to 1997. The average of net radiation was 62 W/m2 with a sensible heat flux of 38 W/m2 and a latent heat flux of 24 W/m2 for these 19 years. Sensible heat flux peaks in May or June at a range of 54-76 W/m2, and latent heat flux in July or August at 41-83 W/m2. The variations of annual precipitation are large, hence the annual total difference between the precipitation and evaporation varies from 8 mm in a low precipitation year to 217 mm in a high precipitation year.
Surface air temperatures were higher in 1998 than in 1997. Western Tibet was drier, and eastern Tibet was wetter, in 1998 than in 1997. The wetness index (WI) distribution agrees well with the distribution of the normalized difference vegetation index (NDVI). Results were also compared to precipitable water (from the NASA Water Vapor Project, NVAP) in the atmosphere.
Submittal Information
Name :
Date :
Dr. Jianqing XU
26-Jul-04-12:08:09
Organization :
Theme :
Frontier Research Center for Global Change (FRCGC)
Theme 5
Address :
Presentation :
3173-25 Showa-machi, Kanazawa-ku, Yokohama City, Kanagawa 236-0001, Japan