Microphysical Structure of Winter Monsoon Cloud Clusters

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  • 1 Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195
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Abstract

Images of hydrometeors in the size range 0.1 to 1.6 mm were obtained by aircraft in precipitating clouds over the South China Sea during Winter MONEX. These observations document for the first time the particle structures and concentrations in tropical cloud clusters above the 0°C level. The data were obtained under nearly constant atmospheric conditions (altitude 7–8 km, temperature −14 to −19°C). The particle samples were stratified according to the type of precipitation in which they were observed as determined from airborne radar, and according to particle size and shape.

The convective cells in the observed clusters were not unlike cells observed elsewhere. They had typical particle concentrations of 100–300 per liter, and riming was apparently the dominant growth mechanism. Ice multiplication may have been active in the convection.

The stratiform regions of the clusters were microphysically quite distinct from the convective cells. “Strong” stratiform precipitation areas (radar reflectivity greater than 20 dBZ) had typical concentrations of 20–70 per liter, while “weak” stratiform precipitation characterized by reflectivities of 1–20 dBZ and “very weak” stratiform precipitation (reflectivities less than 1 dBZ) had concentrations almost exclusively less than 10 per liter. Vapor grown crystals were found in the stratiform regions. The habits of these vapor grown crystals were consistent with the presence of mesoscale updraft. Particles whose crystal habits could not be definitely identified were referred to as “indeterminable.” In the stratiform regions, the presence of many indeterminable ice particles suggested (but did not prove) that aggregation of ice crystals was an important particle growth mechanism. “Very weak” stratiform precipitation regions exhibited characteristics of dissipating stratiform clouds.

Abstract

Images of hydrometeors in the size range 0.1 to 1.6 mm were obtained by aircraft in precipitating clouds over the South China Sea during Winter MONEX. These observations document for the first time the particle structures and concentrations in tropical cloud clusters above the 0°C level. The data were obtained under nearly constant atmospheric conditions (altitude 7–8 km, temperature −14 to −19°C). The particle samples were stratified according to the type of precipitation in which they were observed as determined from airborne radar, and according to particle size and shape.

The convective cells in the observed clusters were not unlike cells observed elsewhere. They had typical particle concentrations of 100–300 per liter, and riming was apparently the dominant growth mechanism. Ice multiplication may have been active in the convection.

The stratiform regions of the clusters were microphysically quite distinct from the convective cells. “Strong” stratiform precipitation areas (radar reflectivity greater than 20 dBZ) had typical concentrations of 20–70 per liter, while “weak” stratiform precipitation characterized by reflectivities of 1–20 dBZ and “very weak” stratiform precipitation (reflectivities less than 1 dBZ) had concentrations almost exclusively less than 10 per liter. Vapor grown crystals were found in the stratiform regions. The habits of these vapor grown crystals were consistent with the presence of mesoscale updraft. Particles whose crystal habits could not be definitely identified were referred to as “indeterminable.” In the stratiform regions, the presence of many indeterminable ice particles suggested (but did not prove) that aggregation of ice crystals was an important particle growth mechanism. “Very weak” stratiform precipitation regions exhibited characteristics of dissipating stratiform clouds.

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