Surface water temperature, T s, is equal to the temperature of maximal density, here set at Neglecting salinity and pressure effects on density, the homothermal condition is necessarily satisfied when the lake First, the combination of atmospheric cooling and mechanical windĮnergy extracts the heat stored in the warm stratified surface layer and progressively deepens the surface layer to the lake bottom, until the lake The complexity of the process, the different phases can be described as follows. If we exclude very deep lakes, where thermobaric instabilities can increase Both competing processes are driven by atmospheric forcing. The freezing time depends on the amount of heat that was stored in the lake during the summertime and the following rate of heat extraction in fallĪnd winter. While long-term trends regarding the decrease in ice duration are clear, ice phenology time seriesĪre also characterized by strong interannual variability ( Magnuson, 2000) making any short-term prediction of the ice duration challenging. Robust archives for climate changes and delays in the calendar dates of the freezing process and earlier thawing are well documented
Long-term trends in lake ice phenology are indeed Lake ice phenology is listed as an essential climate product by the global climate observing system. Prognostic tool for the phenology of lake freezing. Single calibration parameter, the efficiency of the wind energy transfer to the change of potential energy in the lake. This simple yet physically based model is characterized by a Suggesting a power law dependence of the pre-freezing duration on the energy fluxes. The results, interpreted through an approximate analytical solution of the minimal model, elucidate the general tendency of the system, A statistical characterization of the process is obtained with a Monte Carlo simulation considering random sequences of the energyįluxes. Surface water temperature (LSWT), while stronger wind deepens the surface layer, increasing the heat capacity and thus reducing the rate of decrease More intense cooling does indeed accelerate the rate of decrease of lake They play opposite roles in determining the time required for ice formation andĬontribute to the large interannual variability observed in ice phenology. The model is based on the energy balance involving the two main processes governing the inverse stratification dynamics: cooling of waterĭue to heat loss and wind-driven mixing of the surface layer. Here, we propose a minimal model (SELF) built on sound physical grounds that focuses on the pre-freezing period that goes from mixed conditions (lake temperature at 4 ∘C) to the formation of ice (0 ∘C at theĭimictic lakes. Predicting the freezing time in lakes is achieved by means of complex mechanistic models or by simplified statistical regressions considering