A four-year summertime microburst climatology and relationship between microbursts and cloud-to ground lightning flash rate for the NASA Kennedy Space Center, Florida: 1995-1998

Abstract

In order to ameliorate the forecasting of microbursts, the first summertime microburst climatology in the United States was produced. This climatology was based on a four year wind data base during the summer months (May - September) of 1995-1998 for 50 mesons wind towers that encompasses the KSC. An investigation into the microburst characteristics of frequency, diurnal variation, spatial variation, speed frequency distribution, and the wind direction was accomplished. Finally, an examination into the relationship between microbursts and lightning was conducted. A total of 282 microbursts were observed during this four-year period. There were 114 microburst days with 59 of these days having more than one microburst. The most prominent months of microbursts are June, July, and August with July being the most dominant. Several important characteristics of wind speed and direction were found. The median wind speed was 34 knots. The majority of microburst wind speeds fell within 25 and 44 knots. As the wind increases above 43 knots, the frequency decreases exponentially, reaching virtually zero at 65 knots. The predominant wind direction of the microbursts is from southeast through the west-northwest with a maximum from the southwest. The spatial variation of the microbursts revealed an interesting pattern. Some areas received a substantial amount of microbursts, while others received few, if any. It is hypothesized that this difference is due to the sea breeze interacting with the abundant over breezes causing the formation of convection over the same areas on a daily basis. The diurnal variation also uncovered a revealing pattern. The most favorable time for microbursts is between 1600 UTC (12 P.M. EDT) and 2200 UTC (6 P.M. EDT) with the peak occurring between 2000 UTC (4 P.M. EDT) and 2200 UTC (6 P.M. EDT). Directly after this peak the number of microbursts drops drastically. The investigation into the relationship between lightning and microbursts revealed that in most cases there was an evident increase in the CG flash rate up to 25 minutes prior to the microburst. Moreover, a clear peak omen occurred 5-10 minutes before the microburst. Thus, CG lightning may also improve microburst forecasting.