333 Analysis of Total Lightning Flash Rates Over Florida

Monday, 8 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
Thomas A. Mazzetti, Florida State Univ., Tallahassee, FL; and H. E. Fuelberg

It only takes one lightning flash to injure or cause damage. However, the greater a storm's flash rate, the more likely a destructive flash rate will occur. Although Florida is known as the "Sunshine State", it also contains the greatest lightning flash densities in the United States. This paper examines the spatial and temporal distributions of lightning flash rates over Florida and its immediate surroundings. All IC and CG flashes regardless of peak current or polarity were included in the data set obtained from the Earth Networks Total Lightning Network (ENTLN) for the period 2010-2014. We did not track and monitor the flash rates of individual storms. Instead we superimposed a 0.2 × 0.2o grid (~22 km × 22 km) over the domain and counted flashes within each grid cell at 5-min intervals. The total number of 5-min intervals during the 5-yr period was 525,888. The results should be considered tentative since the study period was only 5 yr. Major findings are 1) Although Florida is the "lightning capital" of the United States, ~300,000 (~57%) of the 5-min intervals during 5-yr study period had less than 0.1% spatial coverage of lightning within the study domain. There were ~900 5-min periods of 5% spatial coverage, ~170 periods of 10% coverage, and ~10 periods of 15% coverage. 2) The distribution of flash rates was highly skewed toward small values. There were only ~2500 (~80) occurrences when the flash rate in a 0.2 × 0.2o grid cell was 50 (100) flashes min-1. The greatest rate was 275 flashes min-1. 3) Large flash rates tended to be associated with 5-min periods during which lightning covered a relatively large percentage of the study domain. However, the relation exhibited considerable scatter and is not robust. 4) The area of greatest flash densities was near Orlando. Its location appears to have shifted from that of earlier studies showing the maximum near Tampa, probably due to changing land use and/or climate change. 5) Greatest average annual flash rates (~3.6 flashes min-1) were located near Orlando with weaker secondary maxima located southwest and southeast of Lake Okeechobee. Smaller average annual flash rates (~2.4 flashes min-1) occurred over North Florida and the Florida Panhandle. 6) The distribution of flash rates over land portions of the domain exhibited much larger values than over surrounding waters. 7) The number of hours with lightning was found to increase from north to south over Florida, with typical values of 80 h yr-1 in the Panhandle to 175 h yr-1 over far South Florida. However, the Orlando area was not an area of enhanced number of hours. 8) Median monthly flash rates remained almost constant during the year because of the great deal of skewness in the distributions. However, January and February exhibited slightly smaller values than the remainder of the year. Mean monthly values exhibited greater variability, ranging from ~2 flashes min-1during June to ~1.2 flashes min-1 during January. 9) Large flash rates > 100 flashes min-1 occurred at any time during the 24 h period, and at any location within the domain. 10) The number of hours with lightning during the assumed 12 h of daytime increases from ~ 70 h yr-1 over the Panhandle to ~200 h yr-1 over far South Florida. Conversely, the greatest number of hours during the assumed 12 h of nighttime (~ 35 h yr-1) is located offshore. Smallest values (~6 h yr-1) are located over the eastern Florida Peninsula, extending farther inland over far South Florida.
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