An Investigation of the Development of Cumulonimbus Systems over South Florida. Part II: In-Cloud Structure

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  • 1 NOAA, Environmental Sciences Group, Weather Research Program, Boulder, CO 80303
  • | 2 Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Coral Gables, FL 33149
  • | 3 National Center for Atmospheric Research, Boulder, CO 80307
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Abstract

The in-cloud structure of radar reflectivity and vertical velocity from Doppler radar measurements are described for two cumulonimbus systems that developed over the FACE-1975 surface mesonetwork area on a case study day, 25 August 1975. Results imply a strong interrelationship between updraft velocity and water loading in convective storm development and show the importance of boundary layer forcing in the development of convective clouds in the Florida environment. Analysis of the temporal evolution of cloud mass at 600-m intervals in the vertical shows that below 3 km the two cumulonimbus systems appeared to evolve to about the same size, with significant differences occurring above that level. The increase cloud mass at some levels above 3 km in the second convective system (System II) were more than twice as large as the increase in cloud mass for the first convective system (System I). The difference in the vertical structure of cloud mass in these systems appears to be caused by the differences in the magnitude of the low-level updraft velocities. Approximately 7–10% of the area in the lower portions of System II had updrafts ≥5 m s−1 compared with only 2–3% for System I. These differences in low-level updraft velocity are then related to the differences in boundary layer forcing determined in Part I.

Abstract

The in-cloud structure of radar reflectivity and vertical velocity from Doppler radar measurements are described for two cumulonimbus systems that developed over the FACE-1975 surface mesonetwork area on a case study day, 25 August 1975. Results imply a strong interrelationship between updraft velocity and water loading in convective storm development and show the importance of boundary layer forcing in the development of convective clouds in the Florida environment. Analysis of the temporal evolution of cloud mass at 600-m intervals in the vertical shows that below 3 km the two cumulonimbus systems appeared to evolve to about the same size, with significant differences occurring above that level. The increase cloud mass at some levels above 3 km in the second convective system (System II) were more than twice as large as the increase in cloud mass for the first convective system (System I). The difference in the vertical structure of cloud mass in these systems appears to be caused by the differences in the magnitude of the low-level updraft velocities. Approximately 7–10% of the area in the lower portions of System II had updrafts ≥5 m s−1 compared with only 2–3% for System I. These differences in low-level updraft velocity are then related to the differences in boundary layer forcing determined in Part I.

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