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The surface energy balance directly affects vertical gradients in temperature and specific humidity within the atmospheric surface layer, and these gradients influence optical turbulence. This study was conducted to improve current understanding of the partitioning of energy at the ground surface of a bare soil field and its influence on the character and intensity of optical turbulence as represented by the refractive index structure parameter, C 2 , and to improve micrometeo-rological models of the surface energy balance. The field study entitled "Radiation Energy Balance Experiment for Imagery and Electromagnetic Propagation" was conducted by the United States Army Atmospheric Sciences Laboratory and the United States Department of Agriculture Agricultural Research Service, at Bushland, Texas, during May and July 1992. The following were collected: diurnal radiation; evaporation (directly measured by large weighing lysimeters); five-level micrometeorological profiles of wind speed, air temperature, and relative humidity; soil temperature and volumetric water content; soil heat flux; optical turbulence (scintillometer); and near-and far-field infrared imager data over wet and dry bare soil for clear and cloudy sky conditions. Initial results from the modeling efforts indicate excellent agreement between measured and modeled values of radiation/energy balance fluxes andC 2 , for one day. Future model evaluation will extend over the wide range of conditions encountered during the field study.

No abstract

Advantages of using a fast sampling rate for providing raw data for computing wind velocities from pilot-balloon observations are discussed. Two independent approaches show that (for a given sampling rate) the errors in the mean wind computed through. a layer tend to be smaller the larger the layer. However, if many observations are used to compute the mean wind through a layer, the computed wind is more accurate than that obtained by using just two observations, one a t the bottom and one a t the top of the lnyer. Graphs are presented which give relative estimates of wind errors as a function of sampling interval, sampling rate, and mean wind speed.