P2.12
The Influence of the El Niņo -Southern Oscillation on Cloud-to-Ground Lightning Activity along the Gulf Coast of the United States
Mark LaJoie, NPS, Monterey, CA; and A. Laing, S. Reader, and K. Pfeiffer
Abundant literature exists on both ENSO and lightning individually. This study investigates the dependencies of lightning on ENSO. An eight-year dataset (1995-2002) of cloud-to-ground (CG) lightning flashes was analyzed to determine if the El Nino-Southern Oscillation (ENSO) cycle influences lighting activity along the Gulf Coast region of the United States. Flash density maps were constructed for the complete period of record, individual months, and all the winter and summer seasons. These maps were compared with past lightning climatologies and the one known study linking ENSO with the number of thunderstorm days. Following the qualitative review, Pearson's correlations were computed between concurrent monthly pairings of NINO 3.4 SST and CG lightning flash deviation. The correlation results were visualized in ArcMap GIS, and analyzed both qualitatively and quantitatively.
Monthly mean flash density findings were, overall, consistent with previous United States climatologies. The overall mean for this study was, however, less than other studies. This was, perhaps, due to a greater number of cool ENSO periods when compared with previous lightning climatologies. The analysis of winter season lightning flash densities indicated the influence of the ENSO cycle. This is especially evident for the El Nino winter of 1997-1998 when a marked increase in lighting activity was observed. Overall flash densities decreased during La Nina winters.
For January and February areas of high correlation between NINO 3.4 SST anomaly and CG lightning flash deviation were spatially coincident with areas of enhanced flash density. Both the enhanced CG flash regions and high correlation values and patterns are indicative of a southerly shift in the mid-latitude storm track known to occur during warm ENSO events. High correlation values existed in June and July for isolated pockets of the study area, but it was difficult to attribute these to ENSO. The summer months did not have as great a response to SST anomalies as the winter months. Most of the domain has low correlation values. August stood out as having a large area of negative correlation perhaps indicating a decrease in convective activity during El Nino summers.
These findings have implications for hazard assessment of public safety and can be a useful tool for long-term seasonal planning.
Poster Session 2, Poster Session 2
Tuesday, 11 January 2005, 9:45 AM-11:00 AM
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