PARTITION OF SENSIBLE HEAT FLUXES INTO BASE SOIL AND THE ATMOSPHERE

Energy exchanges between a bare soil and the atmosphere depend on both soil parameters and meteorological conditions. The present work has b een designed to describe the sensible heat partition between soil and the atmosphere, and to develop simple methods for calculating soil hea t flux from soil properties and meteorological data. The relative infl uences of soil properties acid meteorological conditions on the soil e nergy balance were determined in three fields during sugar beet establ ishment (April-May) in Northern France in 1991. The three soils differ red in their texture (sandy loam, loamy and chalky soils), and consequ ently in albedo, thermal and hydraulic properties. Soil heat fluxes we re estimated by the heat storage method using soil temperature, water content and bulk density measured between soil surface and 0.5 m, Soil heat capacity was estimated from the soil water content and bulk dens ity. Soil thermal conductivity was determined from measurements of soi l heat flux and temperature gradients. Atmospheric sensible heat flux was estimated by a two levels aerodynamic method, Solar and net radiat ions were measured continuously, Meteorological conditions and soil pr operties variations induced different magnitude of soil and atmospheri c sensible heat fluxes. Diurnal soil heat fluxes varied with soil ther mal conductivity, and atmospheric heat fluxes varied with albedo, The daily ratios of soil heat flux and atmospheric sensible heat flux to n et radiation, like that of soil to atmospheric sensible heat flux, wer e not constant. They were a function of wind speed at daily time scale . To calculate hourly soil heat fluxes, a simple sinusoidal function w as introduced to account for the phase shift between soil heat flux an d net radiation or atmospheric sensible heat flux. The hourly soil hea t flux was then calculated as the product of its diurnal ratio to net radiation, that can be estimated from wind speed measurements, by the sinusoidal function. This provided calculations of the soil heat flux with a satisfactory accuracy for soils where the surface is dry, and w here there is little evaporation.