The radiative environment of the Tibetan Plateau

The Tibetan Plateau, also known as the QinghaiTibetan Plateau, is a vast elevated plateau in Central Asia. It occupies an area of around 2.3 millionkm2 and has an average elevation of over 4500m. The plateau is interspersed with mountain ranges, has a strong thermal effect on its atmospheric environment, and influences regional and global climate. As the depth of the atmosphere over the plateau is much smaller than its surroundings, the impact of solar radiation on heating the plateau is magnified. At present, observations of shortwave (SW) fluxes over the plateau are very meager and satellite estimates are very coarse. Therefore, estimating the role of radiation in the total heat budget of the plateau is difficult. We use an updated version of the University of Maryland Surface Radiation Budget model driven with observations from Meteosat-5 to characterize clouds and surface SW radiative fluxes at high-temporal and spatial resolution (hourly at 0.125 degrees). Results are presented for a period of 5years in terms of means and variability in space, time, and the context of the regional monsoon regimes. Maximum monthly mean values of SW flux near 360Wm-2 occur in May and June, mainly in the western plateau. Minimum values of 120-150Wm-2 are most widespread in December and January. An anomaly in clouds and SW fluxes in the plateau during the Indian monsoon drought year of 2002 is discovered and discussed. The objective of this study is to provide improved estimates of cloud amounts and radiative fluxes over the plateau in unprecedented detail and with consideration of the plateau conditions. It is anticipated that this information will be useful as a benchmark for the evaluation of numerical models that are known to have difficulties in this complex region and for hydrological modelling.