Numerical Study of the Thermal Structure and Circulation in a Large and Deep Dimictic Lake Over Tibetan Plateau

Abstract

AbstractA three‐dimensional (3‐D) hydrodynamic model based on the Princeton Ocean Model (POM) was applied to simulate the thermal structure and circulation of Lake Nam Co (LNC), the third largest lake over the Tibetan Plateau (TP), during May–December 2013. Compared with a spatially distributed set of one‐dimensional thermal diffusion lake models, POM better reproduced the observed seasonal evolution of the horizontal distribution of lake surface temperature and the vertical thermal structure. A heat budget analysis confirmed that the lateral heat exchange made significant contributions to the horizontal variability of lake temperature. The model results showed that LNC was thermally stratified in summer, had a weak inverse stratification since mid‐December, and was fully turned over during late spring and autumn. During both overturning phases, the modeled “thermal bar” was developed as a result of the density‐driven convection in response to the radiative heating (surface cooling) during spring (autumn). The 3‐D model results showed that the monthly mean circulation featured a predominant mid‐lake cyclonic gyre throughout the ice‐free period; upwelling along the western coast and strong coastal currents occurred in all months except in July–August. Model sensitivity experiments confirmed that the lake circulation was primarily driven by the barotropic dynamics of the prevailing southwesterly wind, while the baroclinic process made a secondary contribution. The results pointed out the necessity to resolve lateral processes when modeling large TP lakes.