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Microphysical Observations in Summer MONEX Convective and Stratiform Clouds

John F. GamacheNOAA/AOML/Hurricane Research Division, Miami, Florida

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Abstract

Two-dimensional images of ice particles observed by a NOAA WP-3D research aircraft during the Summer Monsoon Experiment (SMONEX) are examined. These images were obtained in the temperature interval from −25° to 0°C. The particle structures and size distributions found in convective and stratiform clouds are compared.

Branched crystals were located predominantly in stratiform clouds while column-shaped crystals were located commonly in both stratiform and convective clouds. Stratiform clouds, particularly those observed at temperature warmer than −7°C, had a much greater percentage concentration of large ice particles (>0.8 mm in diameter), and many of these ice particles were aggregates or branched crystals. The importance of aggregation and deposition above the melting level in the stratiform clouds is strongly suggested by these findings.

Ice particle number concentrations measured with the cloud probe were often very high in convective clouds, with a maximum value of approximately 800 L−1. The average convective-cloud concentration was approximately 230 L−1, while the average concentration in the stratiform clouds was approximately 20 L−1. Liquid water was almost completely absent in the convective updrafts, at temperatures between −10° and −22°C. This suggests that the convective updrafts may have been nearly completely glaciated, and the microphysics were dominated by deposition.

The high particle concentrations in the convective updrafts suggest that the updrafts may provide most of the ice particles found in the stratiform cloud. Significant modification in particle structures and size distributions have occurred, however, by the time these suspended particles fall out of the stratiform clouds. These modifications appear to arise from aggregation and deposition.

Abstract

Two-dimensional images of ice particles observed by a NOAA WP-3D research aircraft during the Summer Monsoon Experiment (SMONEX) are examined. These images were obtained in the temperature interval from −25° to 0°C. The particle structures and size distributions found in convective and stratiform clouds are compared.

Branched crystals were located predominantly in stratiform clouds while column-shaped crystals were located commonly in both stratiform and convective clouds. Stratiform clouds, particularly those observed at temperature warmer than −7°C, had a much greater percentage concentration of large ice particles (>0.8 mm in diameter), and many of these ice particles were aggregates or branched crystals. The importance of aggregation and deposition above the melting level in the stratiform clouds is strongly suggested by these findings.

Ice particle number concentrations measured with the cloud probe were often very high in convective clouds, with a maximum value of approximately 800 L−1. The average convective-cloud concentration was approximately 230 L−1, while the average concentration in the stratiform clouds was approximately 20 L−1. Liquid water was almost completely absent in the convective updrafts, at temperatures between −10° and −22°C. This suggests that the convective updrafts may have been nearly completely glaciated, and the microphysics were dominated by deposition.

The high particle concentrations in the convective updrafts suggest that the updrafts may provide most of the ice particles found in the stratiform cloud. Significant modification in particle structures and size distributions have occurred, however, by the time these suspended particles fall out of the stratiform clouds. These modifications appear to arise from aggregation and deposition.

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