A 3-year dataset of sensible and latent heat fluxes from the Tibetan Plateau, derived using eddy covariance measurements

Abstract

The Tibetan Plateau (TP) has become a focus of strong scientific interest due to its role in the global water cycle and its reaction to climate change. Regional flux estimates of sensible and latent heat are important variables for linking the energy and hydrological cycles at the TP’s surface. Within this framework, a 3-year dataset (2008–2010) of eddy covariance measured turbulent fluxes was compiled from four stations on the TP into a standardised workflow: corrections and quality tests were applied using an internationally comparable software package. Second, the energy balance closure (CEB) was determined and two different closure corrections applied. The four stations (Qomolangma, Linzhi, NamCo and Nagqu) represent different locations and typical land surface types on the TP (high altitude alpine steppe with sparse vegetation, a densely vegetated alpine meadow, and bare soil/gravel, respectively). We show that the CEB differs between each surface and undergoes seasonal changes. Typical differences in the turbulent energy fluxes occur between the stations at Qomolangma, Linzhi and NamCo, while Nagqu is quite similar to NamCo. Specific investigation of the pre-monsoon, the Tibetan Plateau summer monsoon, post-monsoon and winter periods within the annual cycle reinforces these findings. The energy flux of the four sites is clearly influenced by the Tibetan Plateau monsoon. In the pre-monsoon period, sensible heat flux is the major energy source delivering heat to the atmosphere, whereas latent heat flux is greater than sensible heat flux during the monsoon season. Other factors affecting surface energy flux are topography and location. Land cover type also affects surface energy flux. The energy balance residuum indicates a typically observed overall non-closure in winter, while closure (or ‘turbulent over-closure’) is achieved during the Tibetan Plateau summer monsoon at the Nagqu site. The latter seems to depend on ground heat flux, which is higher in the wet season, related not only to a larger radiation input but also to a thermal decoupling of dry soils. Heterogeneous landscape modelling using a MODIS product is introduced to explain energy non-closure.