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Turbulence Structure of Arctic Stratus Clouds Derived from Measurements and Calculations

Jörg E. FingerGerman Aerospace Research Establishment (DLR), Institute of atmospheric Physics, Oberpfaffenhofen, Federal Republic of Germany

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Peter WendlingGerman Aerospace Research Establishment (DLR), Institute of atmospheric Physics, Oberpfaffenhofen, Federal Republic of Germany

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Abstract

Results are presented from a detailed case study of an Arctic stratus cloud over the Fram Strait that is based on aircraft measurements and model calculations. The measurements have been performed during MIZEX 1984 (Marginal Ice Zone Experiment) and include high frequency data of meteorological parameters and low frequency measurements of radiation fluxes and cloud microphysical data. The vertical mean structure of the Arctic cloud-topped-planetary boundary layer and the turbulence structure are analyzed and discussed. The main processes that contribute to the turbulent kinetic energy are identified by comparison of the measurements with the results of a one dimensional turbulence model with second-order closure. The radiative cooling at cloud top is identified to be the dominant process controlling the whole turbulence structure for the case of a quasi steady state boundary layer. In this fully developed regime the energy consuming entrainment is sustained by the shear-produced horizontal velocity variance via pressure velocity correlation.

Abstract

Results are presented from a detailed case study of an Arctic stratus cloud over the Fram Strait that is based on aircraft measurements and model calculations. The measurements have been performed during MIZEX 1984 (Marginal Ice Zone Experiment) and include high frequency data of meteorological parameters and low frequency measurements of radiation fluxes and cloud microphysical data. The vertical mean structure of the Arctic cloud-topped-planetary boundary layer and the turbulence structure are analyzed and discussed. The main processes that contribute to the turbulent kinetic energy are identified by comparison of the measurements with the results of a one dimensional turbulence model with second-order closure. The radiative cooling at cloud top is identified to be the dominant process controlling the whole turbulence structure for the case of a quasi steady state boundary layer. In this fully developed regime the energy consuming entrainment is sustained by the shear-produced horizontal velocity variance via pressure velocity correlation.

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