Water Temperature Evolution Driven by Solar Radiation in an Ice-Covered Lake: A Numerical Study and Observational Data

Abstract

Until now, the phenomenon of radiatively driven convection (RDC) in ice-covered lakes has not been sufficiently studied, despite its important role in the functioning of aquatic ecosystems. There have been very few attempts to numerically simulate RDC due to the complexity of this process and the need to use powerful computing resources. The article presents the results of Large Eddy Simulations (LES) of RDC with periodic external energy pumping, which imitates the diurnal variations in solar radiation in the subglacial layer of lakes in spring. The research is aimed at numerically studying the initial stages in the formation and development of a convective mixed layer (CML). A numerical calculation was carried out for three variants of external energy pumping that differed in intensity. A diurnal acceleration and suppression of RDC due to a change in external pumping was revealed for all three variants. The results of numerical simulations provide estimates of such integral parameters of RDC development as the rate of deepening of the lower boundary of the CML, and the rate of water temperature rise within this layer. It was shown that as the cumulative heating of the CML increases over several days, daily increments in temperature and depth slowed down; that is, the dependence of the integral RDC parameters on external pumping was nonlinear. The LES results on RDC parameters were in good agreement with our observational data.