DETERMINATION OF SURFACE FLUXES FROM THE SURFACE RADIATIVE TEMPERATURE

This study examines the bulk aerodynamic method for estimating surface fluxes of heat and moisture using the surface radiative temperature. The surface radiative temperature is often the only available surface temperature from field measurements. Models typically predict heat flu xes from the surface radiative temperature computed from the surface e nergy balance. In this study, the corresponding radiometric exchange c oefficient and radiometric roughness height are computed from tower- a nd low-level aircraft data taken during four different field programs. The data analysis shows that the radiometric exchange coefficient doe s not increase with increasing instability. This is because the radiom etric exchange coefficient must compensate for the large vertical temp erature difference resulting from use of the surface radiative tempera ture. The data analysis and scaling arguments indicate that the radiom etric exchange coefficient for heat in the bulk aerodynamic formulatio n is closely related to theta()/Delta theta for both stable and unsta ble conditions, where Delta theta is the difference between the surfac e radiative temperature and the air temperature and theta() is the ne gative of the heat flux divided by the surface friction velocity. Appl ication of Monin-Obukhov similarity theory with surface radiative temp erature also reduces to a relatively circular internal relationship be tween the radio,netric roughness height and theta()/Delta theta. This roughness height is flow dependent and not systematically related to the roughness height for momentum. As an additional complication. the observed radiometric exchange coefficient for heat depends on the rela tionship between the measured surface radiative temperature and the mi croscale distribution of surface radiative temperature in the footprin t of the heat flux measurement. Analogous problems affect the predicti on of the moisture Aux based on the saturation vapor pressure at the s urface radiative temperature.