The significance of surface temperature patterns on the energy balance of a small lake in the Canadian Shield

Abstract

Temperature patterns of a small lake in the Canadian Shield are examined by means of thermal imagery. The effect of the different surface temperatures on the daytime energy balance is examined for two points over the lake at the time the thermal imagery was taken. For 14 June 1979, two distinct energy balance regimes are noted. At the lake centre, where the deeper water registers a relatively cool thermal signature, a boundary‐layer inversion is observed. The downward sensible heat flux augments the net radiation, and the latent heat flux is 105% of the radiant input. Along the lake margins, the shallows register warm thermal signatures and a lapse profile is observed. The sensible heat flux is an energy sink and the latent heat flux is diminished to 88% of the net radiation. This difference indicates that a single point estimate may introduce a bias if it is assumed to be representative of the lake average for the purposes of studying lake evaporation.

The calculation of the latent heat flux and evaporation is very sensitive to the value of the surface temperature. When the spatial patterns of surface temperature are considered in an estimate of the lake evaporation, the spatially integrated value differs by —6% from the estimate based upon a single point observation at the lake centre for a mid‐day in June and by +10% from the estimate based upon observations collected over the warm shallows.