Diagnosis of Cloud Mass and Heat Fluxes from Radar and Synoptic Data

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

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Chee-Pong Cheng Department of Atmospheric Sciences, University of Washington, Seattle 98195

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Collen A. Leary Department of Atmospheric Sciences, University of Washington, Seattle 98195

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John F. Gamache Department of Atmospheric Sciences, University of Washington, Seattle 98195

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Abstract

A set of equations for diagnosing the properties of precipitating clouds over a tropical ocean is developed by postulating a population of model clouds in which the vertical motions consist of convective up-drafts and downdrafts in cumulus-scale cells and mesocscale updrafts and downdrafts associated with anvil clouds. The properties of a population of precipitating clouds can be diagnosed with these equations by constraining the model clouds to explain either an observed large-scale heat budget (the synoptic approach) or an observed spectrum of precipitation (the radar approach). The results of either approach are dependent on certain parameters of the model clouds, which must be assumed. These parameters are identified, and, in this paper, they are held constant in a controlled experiment comparing the results of the radar and synoptic approaches obtained for the same cloud population (the average population in Phase 111 of GATE). This experiment shows that similar results can be obtained by either approach, giving confidence in both sets of data, the methods used to analyze them and the diagnostic equations themselves. In this experiment, however, the model parameters were adjusted to suppress the diagnosis of the mesoscale motions associated with precipitating anvil clouds. In other papers, the model parameters will be varied to test the model dependency of the diagnostic calculations, especially with regard to the inclusion of mesoscale motions.

Abstract

A set of equations for diagnosing the properties of precipitating clouds over a tropical ocean is developed by postulating a population of model clouds in which the vertical motions consist of convective up-drafts and downdrafts in cumulus-scale cells and mesocscale updrafts and downdrafts associated with anvil clouds. The properties of a population of precipitating clouds can be diagnosed with these equations by constraining the model clouds to explain either an observed large-scale heat budget (the synoptic approach) or an observed spectrum of precipitation (the radar approach). The results of either approach are dependent on certain parameters of the model clouds, which must be assumed. These parameters are identified, and, in this paper, they are held constant in a controlled experiment comparing the results of the radar and synoptic approaches obtained for the same cloud population (the average population in Phase 111 of GATE). This experiment shows that similar results can be obtained by either approach, giving confidence in both sets of data, the methods used to analyze them and the diagnostic equations themselves. In this experiment, however, the model parameters were adjusted to suppress the diagnosis of the mesoscale motions associated with precipitating anvil clouds. In other papers, the model parameters will be varied to test the model dependency of the diagnostic calculations, especially with regard to the inclusion of mesoscale motions.

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