More on the Bowen Ratio over Saturated Surfaces

            The Bowen ratio, Bo, is the ratio of the sensible heat flux (H_s) at the surface to the latent heat flux (H_L).  It occurs regularly in studies of the surface energy budget, can serve as a quality control for measurements or model values of H_s and H_L, and may provide a key to deducing the surface heat fluxes over sea ice and the open ocean from satellite data.

            Over surfaces like sea ice and the open ocean, where the water vapor at the surface is in saturation at the surface temperature, the Bowen ratio is tightly constrained.  Here we investigate these constraints using almost 4000 eddy-covariance measurements of H_s and H_L over Arctic and Antarctic sea ice and another 4000 measurements over the open ocean made by low-flying aircraft.  Over 90% of these data fall into just three regimes:  H_s > 0, H_L > 0; H_s < 0, H_L < 0; and H_s < 0, H_L > 0.

            In our datasets, surface temperature spans –41° to 32°C and primarily predicts the value of the Bowen ratio through a parameter that we call Bo_*, which also depends weakly on surface salinity and barometric pressure.  For the temperature limits above, Bo_* ranges from 45 to 0.25, respectively; and the average measured Bowen ratios are approximately equal to this value (or its negative).  In this presentation, we will use theory and the data to elaborate on the statistical prediction of the Bowen ratio over saturated surfaces from Bo_*.