Cloud‐to‐ground lightning and surface rainfall in warm‐season Florida thunderstorms

Abstract

Relationships between cloud‐to‐ground (CG) lightning and surface rainfall have been examined in nine isolated, warm‐season thunderstorms on the east coast of central Florida. CG flashes and the associated rain volumes were measured as a function of time in storm‐centered reference frames that followed each storm over a network of rain gauges. Values of the storm‐average rain volume per CG flash ranged from 0.70 × 104 to 6.4 × 104 m3/CG flash, with a mean (and standard deviation) of 2.6 × 104 ± 2.1 × 104 m3/CG flash. Values of the rain volume concurrent with CG flashes ranged from 0.11 × 104 to 4.9 × 104 m3/CG flash with a mean of 2.1 × 104 ± 2.0 × 104 m3/CG flash. The lag‐time between the peak CG flash rate and the peak rainfall rate (using 5 min bins), and the results of a lag correlation analysis, show that surface rainfall tends to follow the lightning (positive lag) by up to 20 min in six storms. In one storm the rainfall preceded the lightning by 5 min, and two storms had nonsignificant lags. Values of the lagged rain volume concurrent with CG flashes ranged from 0.43 × 104 to 4.9 × 104 m3/CG flash, and the mean was 1.9 × 104 ± 1.7 × 104 m3/CG flash. For the five storms that produced 12 or more flashes and had significant lags, a plot of the optimum lag time versus the total number of CG flashes shows a linear trend (R2 = 0.56). The number of storms is limited, but the lag results do indicate that large storms tend to have longer lags. A linear fit to the lagged rain volume vs. the number of concurrent CG flashes has a slope of 1.9 × 104 m3/CG flash (R2 = 0.83). We conclude that warm‐season Florida thunderstorms produce a roughly constant rain volume per CG flash and that CG lightning can be used to estimate the location and intensity of convective rainfall in that weather regime.