Babel, W*; Biermann, T; Chen, Y; Yang, K; Thiem, E; Chen, X; Ma, W; Ma, Y; Foken, T: Site specific modelling of turbulent fluxes at Nam Co, Tibetan Plateau – implications for representativeness of flux measurements
Talk, Terrestrial Water Cycle Observation and Modeling from Space – Innovation and Reliability of Data Products WATGLOBS, Beijing, China: 2013-04-25 - 2013-04-30

Surface fluxes over the Tibetan Plateau play a prominent role in the East Asian circulation system. Regional modelling of these fluxes usually do not consider existing small-scale heterogeneities of soil moisture. Regional estimates based on remote sensing data have to be validated with ground based measurements and have to rely on the assumption that these measurements are representative for the respective grid cell. In a case study at the Nam Co Monitoring and Research Station for Multisphere Interactions (NAMORS), operated by the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, the land surface scheme SEWAB is adapted to the typical conditions of the Tibetan Plateau. Turbulent fluxes (sensible and latent heat) were simulated for two adjacent sites nearby the Nam Co lake, a dry alpine steppe site and a wet alpine meadow site. Simulations incorporate the original and the adapted model version, soil properties were described with default parameter sets on the one hand, and parameter derived by laboratory measurements on the other hand. The results have been compared with carefully checked eddy-covariance observations from both sites. The turbulent flux observations have been corrected according to the measured energy balance closure gap and particular attention has been paid to the closure correction method. Furthermore, flux measurements from a shallow lake in the vicinity of NAMORS have been utilized to validate lake surface flux simulations from a hydrodynamic multilayer model. The investigation shows, that SEWAB is able to represent fluxes for both surfaces reasonably well. The adaptation of the model to Tibetan Plateau conditions increased model performance, while the measured parameter did not appear to be superior to the default parameter. Large variation is attributed to the energy balance closure correction of the observations. This should be taken into account, whenever validating model performance with eddy-covariance measurements. The simulated time series of turbulent fluxes over the two land surfaces and the lake surface illustrate the landscape heterogeneity in the vicinity of NAMORS. When using flux data from this station as ground truth for remote sensing products, the desired grid cell should be carefully analysed with respect to the land use types involved on subgrid scale.

last modified 2013-05-06