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Dynamical-Microphysical Evolution of a Convective Storm in a Weakly-Sheared Environment. Part I: Microphysical Observations and Interpretation

James E. DyeNational Center for Atmospheric Research, Boulder, CO 80307

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Brooks E. MartnerDepartment of Atmospheric Science, University of Wyoming, Laramie 82071

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L. Jay MillerNational Center for Atmospheric Research, Boulder, CO 80307

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Abstract

Aircraft measurements of microphysical thermodynamic, and vertical air motion properties supplemented by radar measurements of reflectivity structure are used to investigate precipitation development throughout much of the life cycle of a moderately intense convective storm in northeast Colorado. There was considerable variability of cloud properties such as updraft speed at scales of a few hundred meters early in the life of the storm. Greater organization was evident in the later, more mature stage.

The earliest radar return from a major cell came from particles larger than 1 mm diameter in concentrations less than 10 m−3. It is suggested that these particles must have already followed complicated growth trajectories even at this early stage of the storm, including more than one ascent in updraft.

In the more mature stage of the storm millimetric water drops and partially melted and refreezing ice particles were observed at 1 to 2 km above cloud base in both mixed and unmixed regions of the main updraft. Because of their size and proximity to cloud base, these particles could not have grown during a single ascent in the updraft. The observations suggest that penetrative downdrafts, sedimentation, growth in weak updrafts, and recycling, among others, acted singly or in concert to increase particle growth times in this cloud, and that individual particles may have spent an appreciable length of time outside of favorable growth regions.

Abstract

Aircraft measurements of microphysical thermodynamic, and vertical air motion properties supplemented by radar measurements of reflectivity structure are used to investigate precipitation development throughout much of the life cycle of a moderately intense convective storm in northeast Colorado. There was considerable variability of cloud properties such as updraft speed at scales of a few hundred meters early in the life of the storm. Greater organization was evident in the later, more mature stage.

The earliest radar return from a major cell came from particles larger than 1 mm diameter in concentrations less than 10 m−3. It is suggested that these particles must have already followed complicated growth trajectories even at this early stage of the storm, including more than one ascent in updraft.

In the more mature stage of the storm millimetric water drops and partially melted and refreezing ice particles were observed at 1 to 2 km above cloud base in both mixed and unmixed regions of the main updraft. Because of their size and proximity to cloud base, these particles could not have grown during a single ascent in the updraft. The observations suggest that penetrative downdrafts, sedimentation, growth in weak updrafts, and recycling, among others, acted singly or in concert to increase particle growth times in this cloud, and that individual particles may have spent an appreciable length of time outside of favorable growth regions.

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