Dual-Doppler Radar Observation and Study of Sea Breeze Convective Storm Development

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  • a Rosenstiel School of Marine and Atmospheric Science, University of Miami, Coral Gables, Fla. 33124
  • | b Establissement D'Éiudes et de Recherches Météorologiques, Météorologie Nationale, Paris, France
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Abstract

This paper presents dual-Doppler radar observations and analysis of the kinematics of a convective storm which developed under sea breeze conditions over the area of Miami, Fla. The method, which is based on simultaneous observations of the precipitation particles' velocities by two Doppler radars installed at two different locations, is discussed. The corrections on the estimate of vertical air velocity due to the terminal velocity of the precipitation particles and the change of air density with altitude are also discussed.

The observational results show that in the early stages of its development, the storm system is composed of many small cells with apparent disorganization of the wind fields. The observed structures are complex and bear little resemblance to those predicted by numerical models of an isolated cell. There is always indication of convergence regions of a transitory nature between the precipitation cells. The motion fields become more organized in time and then exhibit extensive and persistent regions of convergence and divergence, with the convergence most likely found at altitudes above 2.5 to 3 km and the divergence below. At the time of maximum organization of the storm, a substantial increase in radar reflectivity is observed in the vicinity of the freezing level which is associated with a drastic increase of the inflow condition at this level, suggesting that the latent heat release due to freezing plays an important part in the storm dynamics at this stage of the storm development.

Abstract

This paper presents dual-Doppler radar observations and analysis of the kinematics of a convective storm which developed under sea breeze conditions over the area of Miami, Fla. The method, which is based on simultaneous observations of the precipitation particles' velocities by two Doppler radars installed at two different locations, is discussed. The corrections on the estimate of vertical air velocity due to the terminal velocity of the precipitation particles and the change of air density with altitude are also discussed.

The observational results show that in the early stages of its development, the storm system is composed of many small cells with apparent disorganization of the wind fields. The observed structures are complex and bear little resemblance to those predicted by numerical models of an isolated cell. There is always indication of convergence regions of a transitory nature between the precipitation cells. The motion fields become more organized in time and then exhibit extensive and persistent regions of convergence and divergence, with the convergence most likely found at altitudes above 2.5 to 3 km and the divergence below. At the time of maximum organization of the storm, a substantial increase in radar reflectivity is observed in the vicinity of the freezing level which is associated with a drastic increase of the inflow condition at this level, suggesting that the latent heat release due to freezing plays an important part in the storm dynamics at this stage of the storm development.

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