A Stochastic Imprint of Internal Physical Processes in Stratified Lake Temperatures

Abstract

One of the goals of limnology is to develop methods that can explain or predict water motion (e.g., currents and eddies), chemical proccsses, and biological/ecological interactions in a lake from the largest (basin) scale to the smallest (turbulence) scale. A major limitation on physical methods is the need to specify energy transfers and the dissipation at the smaller scales (e.g., internal waves and turbulent motion), furthermore to identify and to quantify the important interactions among organisms and chemicals (Stumm, 1985 and Reynolds, 1994). The goal of this paper is inverse to physical lake process modelling. Using data from high-resolution (in time) thermistor stations in a lake, the objective is to identify different lake strata based on periodicities in the temperature signatures and to explain the stratification of the water column and its response to the wind forcing, daily heating and cooling, mesoscale and seasonal weather patterns, etc. in terms of stochastic temperature imprints. The variability of the "temperature wave spectrum" with depth season is identified and is related to the energy flux from basin-scale waves to shorter internal waves and, ultimately, to dissipation. The lake selected for study is a small lake, Lake McCarrons located in Roseville, Minnesota, at 45° northern latitude in a temperatc, continental climate.