Perturbation Pressure Fields Measured by Aircraft around the Cloud-Base Updraft of Deep Convective Clouds

Margaret A. LeMone National Center for Atmospheric Research, Boulder, Colorado

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Gary M. Barnes National Center for Atmospheric Research, Boulder, Colorado

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James C. Fankhauser National Center for Atmospheric Research, Boulder, Colorado

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Lesley F. Tarleton National Center for Atmospheric Research, Boulder, Colorado

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Abstract

Perturbation pressure fields are measured by aircraft around the cloud base updrafts of seven clouds ranging in size from weak cumulus congestus to intense cumulonimbus during CCOPE (1981). The fields are characterized by a high-low pressure couplet of similar size to the updraft, but a quarter-wavelength out of Phase, with the minimum pressure downshear of the updraft maximum. An estimate of the terms in the Poisson equation for pressure show that the pressure perturbation results chiefly from the interaction of the updraft with the vertical shear of the environmental horizontal wind. The behavior of the pressure oscillation is well predicted by inserting sinusoidal functions in the corresponding terms in the Poisson equation. The amplitude of the pressure oscillation is proportional to the wavelengths of the pressure and vertical-velocity fields, the amplitude of the vertical-velocity oscillation, and the vertical shear of the horizontal environmental wind through cloud base, measured in the direction of the maximum pressure gradient.

Abstract

Perturbation pressure fields are measured by aircraft around the cloud base updrafts of seven clouds ranging in size from weak cumulus congestus to intense cumulonimbus during CCOPE (1981). The fields are characterized by a high-low pressure couplet of similar size to the updraft, but a quarter-wavelength out of Phase, with the minimum pressure downshear of the updraft maximum. An estimate of the terms in the Poisson equation for pressure show that the pressure perturbation results chiefly from the interaction of the updraft with the vertical shear of the environmental horizontal wind. The behavior of the pressure oscillation is well predicted by inserting sinusoidal functions in the corresponding terms in the Poisson equation. The amplitude of the pressure oscillation is proportional to the wavelengths of the pressure and vertical-velocity fields, the amplitude of the vertical-velocity oscillation, and the vertical shear of the horizontal environmental wind through cloud base, measured in the direction of the maximum pressure gradient.

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