Predicting Warm Season Nocturnal Cloud-To-Ground Lightning Near Cape Canaveral, Florida

摘要

Two aspects of nocturnal convection over Florida are examined in this study: A climatology of all warm season nocturnal cloud-to-ground lightning (COL) flashes over east central Florida, and nocturnal COL that develops near Cape Canaveral, Florida during undisturbed conditions. Seven years of warm season (May - October) radiosonde data (1992 - 1998) are used to categorize nights into one of five wind regimes based on the 1000-700 mb mean vector wind. Cloud-to-ground flashes are used to examine the spatial distribution of nocturnal lightning. Flashes are found to occur on 525 of the 825 nights with available soundings. Spatial maps of CGL flashes reveal that most occur over the Gulf Stream. Nights with flow parallel to the peninsula from the south are found to have the greatest percent occurrence of nights with COL flashes. Enhanced midlevel moisture (700 - 500 mb) increases the percent occurrence of nights having COL flashes. Midlevel lapse rates (850 - 500 mb) show little variation among the wind regimes. Streamline analyses reveal that the synoptic flow is crucial in determining thermodynamic characteristics of air over the study area. Data from the local lightning detection network reveal 74 nights during the warm season months of 1995 - 1997 with cloud-to-ground lightning within a 40 km radius of study. Surface analyses are used to eliminate nights with disturbed flow, while radar data are analyzed to eliminate pre-existing convection. A data set of nights without COL (NCOL nights) also is constructed. Stability, temperature, wind, and moisture parameters of the two categories are examined statistically. The 1000 - 800 mb lapse rate is the only temperature related parameter that statistically discriminates between the two categories. Relative humidities at 850, 800, and 750 mb all show statistically significant discrimination between categories. The K-Index is found to have the greatest forecast skill of all the standard stability parameters.