A Process-Oriented Small Lake Scheme for Coupled Climate Modeling Applications

Abstract

one-dimensional dynamic lake model is presented as a candidate for simulating small unresolved lakes within the land surface scheme of a regional or global climate model. This model is based largely on well-established process algorithms with some exceptions. The complete nonlinear surface energy balance is computed in a skin layer of arbitrary thickness in order to ensure rapid response times with the atmosphere. Turbulent mixing in the surface mixed layer is achieved through stirring and buoyancy production as well as shear production along the diurnal thermocline. The net effect of Kelvin?Helmholtz instability on thermocline structure is grossly accounted for by computing a linear temperature profile within a thermocline layer. The energetics of billowing is not considered; however, a significant thermocline leakage term is included. The model has been incorporated into the Canadian Land Surface Scheme and used to estimate regional turbulent sensible and latent heat fluxes over the Experimental Lakes Area in the boreal forest of northwestern Ontario?an area about 30% lake covered. It is demonstrated that the presence of open water has a significant effect on the net flux exchange with the atmosphere in this region. Sensible heat flux to the atmosphere is suppressed during the summer stratified period but enhanced in the fall, resulting in an increased accumulation of about 5% by the end of the open water season due to the presence of lakes. Turbulent latent heat flux to the atmosphere is more enhanced during autumn, with a final accumulation about 24% larger.