The exchange coefficients for latent and sensible heat flux over lakes: Dependence upon atmospheric stability

Components of the energy budget of a small lake were estimated over the autumnal cooling period. Measured values of the stored thermal energy and radiative heating were used to evaluate several bulk formulae for sensible and latent heat transfer. Over 50–100 day intervals, bulk formulae for latent and sensible heat flux without stability corrections were as good as formulae that incorporated such corrections; both satisfactorily reproduced the measured heat storage data. Over shorter (daily to weekly) time-scales, predictions incorporating stability corrections were superior to those without stability corrections. Over daily periods when the atmosphere was nearly neutral or was unstable, a formulation for sensible and latent heat transfer designed for small-scale systems (cooling ponds and reservoirs) agreed closely with the usual large-scale (oceanic) bulk formulations. The corrections for stability in the small-scale formulation are based on laboratory and theoretical studies of free convection; the stability correction in the large-scale formulation uses a bulk Richardson number in a manner consistent with flux-profile theory. Both agreed with the measured data for the unstable and near-neutral cases. Under stable atmospheric conditions (in a daily average sense), both formulations underestimated the measured fluxes