Five years of cloud-to-ground (CG) lightning data (2002 – 2006) from the National Lighting Detection Network (NLDN) are examined to describe the nature of CG lightning in Florida. Our focus is on positive CG lightning (+CG; i.e., that which lowers positive charge from cloud to ground). Flash densities are computed on a 2×2 km grid for +CG and total CG during the warm season (May – September), the cool (cold) season (remaining months), and the entire year. The maximum annual total CG flash density of 28.1 flashes km-2 yr-1 is located just north of Tampa. Relative minima of cool season CG flash density extend from Tallahassee northeastward and south of the Tampa – Cape Canaveral corridor. +CG flash density shows a tendency towards greater values in the northwestern portion of the domain during both seasons. Two relative maxima of +CG flash densities are located near the Apalachicola National Forest in the panhandle (0.5 – 1.05 positive flashes km-2 yr-1), and near Naples in Southwest Florida (0.35 – 0.5 positive flashes km-2 yr-1). The median peak current and number of return strokes (multiplicity) of +CG and –CG flashes are quite different during the cool season, but are more similar during the warm season. The greatest peak current (~ 30 kA) and smallest multiplicity (~ 1.4) of +CG flashes occur during the cool season. The warm season is characterized by the smaller peak current (~ 20 kA) and larger multiplicity (> 1.5) of +CG flashes. Since +CG lightning is generally thought to consist of a single return stroke, our warm season multiplicities of ~1.7 are unexpected. This value may represent cloud pulses that are misclassified by the NLDN as weak peak current +CG flashes, or may actually describe characteristics of the CG lightning. The threshold for classifying these weak positive events recently was increased from +10 kA to +15 kA. An important finding is that greater than 40 % of all positive events (> 10 kA) in Florida during June, July, August, and October ranged between 10 kA – 15 kA. The unusual warm season characteristics of +CG lightning suggest that numerous ambiguous events are retained in our dataset, even when using the new threshold of +15 kA. Daily CG lightning patterns in Jacksonville and Miami were analyzed during March and July 2003. On a given day, there is more +CG lightning during March than July in both Jacksonville and Miami. Also, when lightning does occur, the percentage of positive flashes generally is greater in Jacksonville than Miami. 1.5) of +CG flashes. Since +CG lightning is generally thought to consist of a single return stroke, our warm season multiplicities of ~1.7 are unexpected. This value may represent cloud pulses that are misclassified by the NLDN as weak peak current +CG flashes, or may actually describe characteristics of the CG lightning. The threshold for classifying these weak positive events recently was increased from +10 kA to +15 kA. An important finding is that greater than 40 % of all positive events (> 10 kA) in Florida during June, July, August, and October ranged between 10 kA – 15 kA. The unusual warm season characteristics of +CG lightning suggest that numerous ambiguous events are retained in our dataset, even when using the new threshold of +15 kA. Daily CG lightning patterns in Jacksonville and Miami were analyzed during March and July 2003. On a given day, there is more +CG lightning during March than July in both Jacksonville and Miami. Also, when lightning does occur, the percentage of positive flashes generally is greater in Jacksonville than Miami. 10 kA) in Florida during June, July, August, and October ranged between 10 kA – 15 kA. The unusual warm season characteristics of +CG lightning suggest that numerous ambiguous events are retained in our dataset, even when using the new threshold of +15 kA. Daily CG lightning patterns in Jacksonville and Miami were analyzed during March and July 2003. On a given day, there is more +CG lightning during March than July in both Jacksonville and Miami. Also, when lightning does occur, the percentage of positive flashes generally is greater in Jacksonville than Miami. / A Thesis Submitted to the Department of Meteorology in Partial Fulfillment of the Requirements for the Degree of Master of Science. / Summer Semester, 2007. / June 28, 2007. / Positive Lightning, Multiplicity, Peak Current, Cloud-To-Ground Lightning / Includes bibliographical references. / Henry E. Fuelberg, Professor Directing Thesis; Mark Bourassa, Committee Member; Phillip Cunningham, Committee Member; Andrew I. Watson, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_176395 |
| Contributors | Rudlosky, Scott David (authoraut), Fuelberg, Henry E. (professor directing thesis), Bourassa, Mark (committee member), Cunningham, Phillip (committee member), Watson, Andrew I. (committee member), Department of Earth, Ocean and Atmospheric Sciences (degree granting department), Florida State University (degree granting institution) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource, computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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