Uncertainties in Quantitatively Estimating the Atmospheric Heat Source over the Tibetan Plateau

Abstract

As a huge, intense, and elevated atmospheric heat source (AHS) approaching the mid-troposphere in spring and summer, the Tibetan Plateau (TP) thermal forcing is perceived as an important factor contributing to the formation and variation of the Asian summer monsoon. Despite numerous studies devoted to determine the strength and change of the thermal forcing of the TP on the basis of various data sources and methods, uncertainties remain in quantitative estimation of the AHS and will persist for the following reasons: (1) Routine meteorological stations cover only limited regions and show remarkable spatial inhomogeneity with most distributed in the central and eastern plateau. Moreover, all of these stations are situated at an altitude below 5000 m. Thus, the large area above that elevation is not included in the data. (2) Direct observations on heat fluxes do not exist at most stations, and the sensible heat flux (SHF) is calculated by the bulk formula, in which the drag coefficient for heat is often treated as an empirical constant without considering atmospheric stability and thermal roughness length. (3) Radiation flux derived by satellite remote sensing shows a large discrepancy in the algorithm in data inversion and complex terrain. (4) In reanalysis data, besides the rare observational records employed for data assimilation, model bias in physical processes induces visible errors in producing the diabatic heating fields.