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Vertical structure and kinematics of tropical monsoon precipitation observed from a 2875-MHz profiler during NAME




Lerach, David G., author
Department of Atmospheric Science, Colorado State University, publisher

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Deep cloud systems in the Tropics play a significant role in the global heat budget. This is due to the fact that atmospheric circulations, such as the Hadley and Walker cells, are sensitive to the shape of the diabatic heating profile, which in turn depends on the vertical structure of tropical convective systems. The goal of this project is to create a climatology of the vertical structure of precipitating cloud systems that characterized the 2004 North American monsoon. The study utilized data from the 2875-MHz profiler stationed near Sinaloa, Mexico from early July through mid-September of 2004 for the North American Monsoon Experiment (NAME). The profiler observed 23 rain events. Climatologic frequency distributions of reflectivity, Doppler velocity, and spectral width were created for various precipitation regimes. The NAME distributions compared favorably with results from previous studies. Stratiform precipitation exhibited a radar bright band and a strong Doppler velocity gradient in the melting layer, and weak spectral width above the melting layer. Mixed stratiform/convective regions contained low reflectivity and a weak bright band. Convective profiles contained high reflectivity, large Doppler velocities, and high spectral width. Vertical air motions derived from the 2875-MHz profiler were compared with EVAD and 449-MHz profiler retrievals. The 2875-MHz pro filer vertical air motion estimates contained a negative bias to both methods of approximately 0.5 m s-1. Though the errors in the stratiform vertical air motion estimates were of the same order as the stratiform air motions, the NAME vertical air motion composites for stratiform and mixed stratiform/convective precipitation exhibited similar features to composites from previous studies. However, convective composites from past studies showed ascent throughout the troposphere while the NAME composite showed a significant region of descent between 4 and 6 km. This discrepancy cannot be fully explained by the negative bias of 0.5 m s-1 in the NAME estimates. Climatologic vertical profiles of precipitating clouds were successfully created from the 2875-MHz pro filer NAME dataset for various precipitation regimes. While the vertical air motion estimates yielded unexpected values in the melting layer of convective precipitation, they proved useful in analyzing the vertical structure of vertical air motion for various precipitation regimes in a mean sense as well as assessing general updraft and downdraft intensity in individual convective cells.


Fall 2006.
Includes bibliographical references (pages 100-105).

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Monsoons -- Tropics
Rain and rainfall -- Tropics


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