Modelling the Thermal Structure and Circulations of Lake Nam Co, Central
Tibetan Plateau
Abstract
A three-dimensional (3-D) hydrodynamic model based on Princeton Ocean
Model (POM) and a one-dimensional (1-D) lake model are applied to
simulate the thermal structure and circulations of Lake Nam Co (LNC),
the second largest lake in Tibet. Results show that POM can well
reproduce the seasonal and synoptic variations of the in-situ observed
vertical temperature profile, and the spatial distribution of satellite
estimated lake surface temperature during May-December 2013. However,
without considering the water and energy exchanges related to the lake
hydrodynamics, the 1-D model exhibits much more evident biases in the
lake thermal evolution. These shortages of the 1-D lake model solutions
emphasize that the complex temperature-current interactions must be
accounted for investigating the thermodynamics in large lakes over
Tibet. From both observation and hydrodynamic simulations, LNC is
identified to experience the springtime overturning, warm stratified
phase during early-June to mid-November, autumnal overturning, and weak
inverse stratified phase since mid-December. The two overturning
processes last for about one month and are both related to the thermal
bar development, which is controlled by the density-driven convection
associated with the radiative heating (surface cooling) in spring
(autumn). During the warm stratified phase, the eastern shallow basin is
mainly characterized by anticyclonic circulation and bowl-shaped
thermocline, while the central deep basin is featured by a cyclonic gyre
(eastward currents) and dome-shaped (bowl-shaped) thermocline with the
enhancement (weakness) of thermal stratification. The lake circulation
during December is basically dominated by a single strong cyclonic gyre
in the main lake basin.