Large eddy simulation of boundary-layer turbulence over heterogeneous underlying surfaces in the northeastern Tibetan Plateau

Abstract

<p>The source region of the Yellow River (SRYR) is located in the northeastern of the Tibetan Plateau and is known as the “water tower” of China because it contains 48 lakes. Daytime lake breezes are proved by ERA-Interim reanalysis data in the SRYR. We use the Large Eddy Model to depict the effect of the circulations induced by surface anomaly heating (patches) on the boundary-layer turbulence. A set of 1D tests of strip-like surface heat flux distribution are carried out, which based on observations in the Ngoring Lake basin in the summer of 2012. The simulations show that for the cases without background wind, patch-induced circulations (SCs) promote the growth of convective boundary layer (CBL), enhance the turbulent kinetic energy (TKE), and then modify the spatial distribution of TKE. Based on phase-averaged analysis, which separates the attribution from the SCs and the background turbulence, the SCs contribute no more than 10% to the vertical turbulent intensity, but their contributions to the heat flux can be up to 80%. The thermal internal boundary layer reduces the wind speed and forms the stable stratification, which produces the obvious change of turbulent momentum flux and heat flux over the heterogeneous surfaces. The increased downdrafts, which mainly occur over the lake patches, carry more warm, dry air down from the free atmosphere. The background wind inhibits the SCs and the development of the CBL; it also weakens the patch-induced turbulent intensity, heat flux, and convective intensity.</p>