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  • Author or Editor: J. J. Nucciarone x
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Jeffrey J. Nucciarone and George S. Young

Abstract

Mixed-layer scaling was successfully applied to the velocity, temperature, and moisture spectra of the marine stratocumulus-topped mixed layers observed during the First ISCCP Regional Experiment (FIRE). These turbulence spectra provide considerable insight into the physical phenomena that affect this kind of boundary layer. At least four of these phenomena contribute to the turbulence spectra: eddies that result directly from shear and buoyant production of turbulent kinetic energy (the microscale energy production subrange); smaller eddies that result from the inertial cascade of energy (the inertial subrange); quasi-two-dimensional mesoscale variations; and gravity waves. The velocity, temperature, and moisture spectra are affected differently by each of these phenomena. The turbulence spectra highlight the differences between the cold-current marine stratocumulus-topped boundary layer and the overland convective boundary layer.

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C. Prabhakara, G. Dalu, G. L. Liberti, J. J. Nucciarone, and R. Suhasini

Abstract

Passive microwave measurements made by the Scanning Multichannel Microwave Radiometer (SMMR) and the Special Sensor Microwave/Imager (SSM/I) reveal information about rain and precipitation-sized ice in the field of view (FOV) of the instruments. The brightness temperature T b measured at 37 GHZ, having an FOV of about 30 km, shows relatively strong emission from rain and only marginal effects caused by scattering by ice above the rain clouds. At frequencies below 37 GHz, where the FOV is larger and the volume extinction coefficient is weaker, it is found that the observations made by these radiometers do not yield appreciable additional information about rain. At 85 GHz (FOV ≈ 15 km), where the volume extinction coefficient is considerably larger, direct information about rain below the clouds is generally masked.

Based on the above considerations, 37-GHz observations with a 30-kin FOV from SMMR and SSM/I are selected for the purpose of rain-rate retrieval over oceans. An empirical method is developed to estimate the rain rate in which it is assumed that over an oceanic area the statistics of the observed T b's at 37 GHz in a rain storm are related to the rain-rate statistics in that storm. Also, in this method, the underestimation of rain rate, arising from the inability of the radiometer to respond sensitively to rain rate above a given threshold, is rectified with the aid of two parameters that depend on the total water vapor content in the atmosphere. The rain rates retrieved by this method compare favorably with radar observation. Monthly mean global maps of rain derived from this technique over the oceans are consistent with climatology.

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