The Relationship between Total Area Divergence and Convective Precipitation in South Florida

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  • 1 Weather Research Program, Environmental Research Laboratories, NOAA, Boulder, CO 80303
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Abstract

Total area divergence is related to area rainfall using data collected during the Florida Area Cumulus Experiment (FACE) 1975 field experiment over a network that covered 1440 km2. A convergence event is defined as a monotonic decrease in total area divergence of more than 25×10−6 s−1 for more than ten minutes. This change in total area divergence is related to the total amount of area rainfall considered to be associated with the convergence event. For 121 convergence events during July and August 1975, a correlation coefficient of −0.59 is found between change in convergence and rainfall amount. When the ensemble is subdivided, it is found that for slow moving convective systems, or when low-level winds are weak, there is twice the amount of rainfall per convergence event. When middle-level (850–500 mb) relative humidity is in the range 50–65%, the correlation coefficient between convergence and rainfall is −0.81. Data are also partitioned according to stability and buoyancy. Convective outflow and its reflection in total area divergence are examined, and relationships are developed for determining the amount of precipitation for each divergence event. For the 75 rain events during FACE 1975, a correlation coefficient of 0.75 is found between the change in divergence and the rainfall amount.

Abstract

Total area divergence is related to area rainfall using data collected during the Florida Area Cumulus Experiment (FACE) 1975 field experiment over a network that covered 1440 km2. A convergence event is defined as a monotonic decrease in total area divergence of more than 25×10−6 s−1 for more than ten minutes. This change in total area divergence is related to the total amount of area rainfall considered to be associated with the convergence event. For 121 convergence events during July and August 1975, a correlation coefficient of −0.59 is found between change in convergence and rainfall amount. When the ensemble is subdivided, it is found that for slow moving convective systems, or when low-level winds are weak, there is twice the amount of rainfall per convergence event. When middle-level (850–500 mb) relative humidity is in the range 50–65%, the correlation coefficient between convergence and rainfall is −0.81. Data are also partitioned according to stability and buoyancy. Convective outflow and its reflection in total area divergence are examined, and relationships are developed for determining the amount of precipitation for each divergence event. For the 75 rain events during FACE 1975, a correlation coefficient of 0.75 is found between the change in divergence and the rainfall amount.

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