Tibetan Plateau is considered to have very important roles controlling Asian monsoon. The most prominent feature is the high altitude(around 500m from MSL) extending 2000km horizontally. It has various effects as a extended heat source as well as dynamic effect due to topography. As a result, precipitation is also modified by the plateau. However, the detailed measurement is very few over the plateau, especially, in-situ surface flux measurements have not carried out.
In the present study, in-situ experiments were carried out during the IOP(May-August,1998) as a international project of GAME/Tibet as a subprogram of GEWEX. The period of the IOP was set to include the onset and the end of monsoon. Various kinds of surface measurements were carried out as well as upper air soundings and a doppler radar observation.
The present authors had participated in surface flux measurements over the eastern plateau. Two Flux-PAM systems were introduced from NCAR and installed at two separate sites. One is set on a wet area and another one is set on a dry area. As a flux measurement system, we have adopted GILL/Solent sonic anemometer and Band Pass Covariance algorithm for the latent heat flux evaluation. They both were setup at the beginning of May 1998. During a month after setup, which is a pre-monsoon season, the climate was rather dry and the very clear diurnal wind speed variations were observed with peak gust of 20ms-1. Accordingly, the observed sensible heat flux was very large and the most of the net radiation energy were released to the atmosphere as sensible heat.
As a seasonal march, the monsoon has started and rather moist conditions has predominant. Accordingly, the role of the latent heat flux have increased and the amplitude of the diurnal wind speed variation has decreased in summer.
In additions to the Flux-PAM sites, one fully equipped surface flux system were installed including profile, eddy correlation and radiation measurements. Furthermore, simple automatic weather station(AWS) were setup at four sites. In the present report, the seasonal variation of heat and water circulation is discussed based on the GAME/Tibet experiment