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Henry Rachele and Arnold Tunick

Abstract

The character of temperature and moisture gradients in the atmospheric surface layer is shown to be related to the intensity of visual distortions or “blurring” of images routinely detected by electo-optical systems and sensors. The authors are able to make quantitative approximations of the optical turbulence effect as represented by the refractive-index structure parameter C 2 n. Through the application of Monin-Obukhov similarity, the magnitudes of potential temperature and specific humidity gradients are determined using values of sensible and latent heat fluxes estimated from a semiempirical radiation and energy balance model. The model is constrained to require a minimum number of conventional meteorological inputs at a specific reference level (i.e., 2 m). These measurements include temperature, pressure, relative humidity, and wind speed. The model also requires a judgment of soil type and moisture (dry, moist or saturated), cloud characteristics (tenths of cloud cover, opacity, and an estimate of cloud height), day of the year, time of day, and longitude and latitude of the site of interest. Model concepts and equations are presented and several sample results are illustrated. Model estimates of net radiation; sensible, ground, and latent heat fluxes; and C 2 n are compared with measured values or values derived from measurements.

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Henry Rachele, Arnold Tunick, and Frank V. Hansen

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Henry Rachele, Arnold Tunick, and Frank V. Hansen

Abstract

Methodology for determining the similarity scaling constants for wind, temperature, and specific humidity from micrometeorological tower data is presented. The equations and the approach for solving them are referred to as MARIAH. The MARIAH solution is much simpler than using the traditional O'KEYPS functions primarily due to the elimination of laborious, iterative schemes required for evaluating the diabatic influence functions, dimensionless lapse rate, and dimensionless wind shear. Examples of output are given to demonstrate the equivalency of MARIAH to O'KEYPS.

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Arnold Tunick, Henry Rachele, Frank V. Hansen, Terry A. Howell, Jean L. Steiner, Arland D. Schneider, and Steve R. Evett

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, , and to improve micrometeorological 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 and , for one day. Future model evaluation will extend over the wide range of conditions encountered during the field study.

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