Surface energy budget at Amdo on the Tibetan Plateau using GAME/Tibet IOP98 data

In the east of Tibetan Plateau, Amdo, the surface energy flux measurement with eddy correlation technique was conducted during the Intensive Observation Period (IOP) of GEWEX Asian Monsoon Experiment (GAME). This study is a preliminary analysis on surface energy budget at Amdo with these data. There is a remarkable change in sensible and latent heat fluxes between pre-monsoon season and summer monsoon season. In the pre-monsoon, the ground surface and the surface layer were very dry. The specific humidity was 2 to 4 g/kg and the sensible heat flux was dominant. As the monsoon progresses, the surface becomes wet due to almost daily precipitation. Accordingly, the sensible heat flux decreases and the latent heat flux increases. In the beginning of September, nearly the end of the summer monsoon, the latent heat flux exceeds the sensible heat flux. The ground heat flux at the surface was estimated using the observed soil temperature profile with the aid of the thermal conductive equation. The computed ground heat flux corresponds to the residual of the surface energy balance in the daytime. But disagreement occurred in the evening, when the surface temperature rapidly decreases. On the daily averaged bases, the surface energy balance is not well closed. In terms of closure ratio, the value in a typical clear day was 67%. Another rough estimation of soil heat flux is made, in which the heat needed to melt the soil water and to heat up the soil layer was calculated. According to this, it was estimated that about 30 W/m(2) (20% of net radiation) of soil heat flux was required on average over April 20 to July 20, but the measured soil heat flux was only 5.7 W/m(2).