The Mesoscale and Microscale Structure and Organization of Clouds and Precipitation in Midlatitude Cyclones. III: Air Motions and Precipitation Growth in a Warm-Frontal Rainband

Robert A. Houze Jr. Department of Atmospheric Sciences, University of Washington, Seattle 98195

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Steven A. Rutledge Department of Atmospheric Sciences, University of Washington, Seattle 98195

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Thomas J. Matejka Department of Atmospheric Sciences, University of Washington, Seattle 98195

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Peter V. Hobbs Department of Atmospheric Sciences, University of Washington, Seattle 98195

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Abstract

Doppler radar data and airborne cloud microphysical measurements obtained in the CYCLES PROJECT indicate that a warm-frontal rainband in an extratropical cyclone was characterized by a precipitation process in which clouds at low levels were enhanced by a mesoscale updraft. Ice particles, apparently formed in shallow convective cells aloft and then drifted downward, undergoing aggregation just above the melting layer. This study demonstrates the crucial role of the low-level mesoscale updraft in condensing a sufficient amount of cloud water for particles to accrete as they fell through the lower portion of the frontal cloud.

Abstract

Doppler radar data and airborne cloud microphysical measurements obtained in the CYCLES PROJECT indicate that a warm-frontal rainband in an extratropical cyclone was characterized by a precipitation process in which clouds at low levels were enhanced by a mesoscale updraft. Ice particles, apparently formed in shallow convective cells aloft and then drifted downward, undergoing aggregation just above the melting layer. This study demonstrates the crucial role of the low-level mesoscale updraft in condensing a sufficient amount of cloud water for particles to accrete as they fell through the lower portion of the frontal cloud.

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