Simulation of surface energy fluxes and stratification of a small boreal lake by a set of onedimensional models

摘要

Five one-dimensional (1D) lake models were run for the open water season in 2006 for Lake Valkea-Kotinen(Finland) using on-lake measured meteorological forcing. The model results were validated using measurementsof water temperature and of eddy covariance (EC) fluxes. The surface temperature is satisfactorilysimulated by all models showing slight overestimation (by 0.1-1.1℃). Both sensible and latent heat fluxes arepositively biased in respect to EC data, consistent with earlier studies. However, correlation coefficientsbetween EC-fluxes and those simulated are relatively high ranging from 0.55 to 0.74. The skill to simulatevertical temperature profiles by different models is assessed as well. It is found that the lake modelsunderestimate the EC-derived surface drag coefficient, however providing realistic temperature profiles. It isargued that the real momentum flux from the atmosphere is larger than simulated, however it is split upbetween the wave development and the acceleration of lake currents. Adopting the simple parameterisationfor momentum flux partitioning in one of the models showed that this mechanism can be significant. Finally,the effect of including the lake bathymetry data in k-o models was the drastic overheating of water belowthe thermocline. This is likely to be caused by omitting the heat flux at the lake margins. Thus, theparameterisation of heat flux at the lake’s margins should be included in the models; otherwise it isrecommended to neglect bathymetry effects for such small water bodies as the Lake Valkea-Kotinen.