The Influence of the El Niño–Southern Oscillation on Cloud-to-Ground Lightning Activity along the Gulf Coast. Part II: Monthly Correlations

Abstract

The El Niño?Southern Oscillation (ENSO) cycle is known to influence weather and climate along the Gulf Coast region, causing anomalously high precipitation during El Niño winters. This region is also known for having the highest lightning flash density in the United States. An 8-yr dataset (1995?2002) of cloud-to-ground (CG) lightning flashes was analyzed to determine if the ENSO cycle influences lighting activity along the Gulf Coast region. Simple Pearson?s correlations were computed between concurrent monthly pairings of Niño-3.4 sea surface temperature (SST) and CG lightning flash deviation values from the study area. The correlation results are mapped and analyzed for links to meteorological features. Statistically significant correlation values greater than 0.8 were noted over large swaths of the study area during each winter month. The highest correlations were arranged in banded swaths and associated with regions of low flash densities during December and February. In January, areas of high correlation 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 midlatitude storm track known to occur during warm ENSO events. During the spring and summer, most of the region has weak correlation with ENSO except for August, which has a large area of negative correlations. These findings indicate that lightning increases during La Niña summers. Correlation patterns in late fall are similar to those of winter. The ENSO?lightning relationship has implications for hazard assessment and can be a useful tool for long-term seasonal planning.