GIS User Group

Using GIS to relate ENSO and Cloud-to-Ground Lightning along the United States Gulf Coast
Arlene Laing - MMM/ESSL

Geographic Information System (GIS) and other statistical analysis are employed to determine if the El Niño-Southern Oscillation (ENSO) cycle influences cloud-to-ground (CG) lighting activity along the Gulf Coast region of the United States . The Gulf Coast region is noted for its high flash density and as an area in which the ENSO influence is seen in the temperature and precipitation field. However, little has been published on the relationship of ENSO and lightning. In this study, an eight-year data set (1995-2002) is used to relate Gulf Coast lightning variability to the phases of ENSO.

GIS techniques are used to: (i) map flash density on a 2.5 x 2.5 km grid using Albers Equal Area projection, which preserves area—a key property when analyzing flashes per unit area , (ii) adjust flash density maps for changes in the detection efficiency of the National Lightning Detection Network (NLDN); (iii) estimate new annual domain totals using zonal statistics; and (iv) map correlations of monthly flash deviations with sea surface temperature (SST) anomalies in the equatorial Pacific NIÑO 3.4 region.

The highest annual lightning counts were observed in 1997, which had mostly warm ENSO seasons, and the 1997-98 El Ni ñ o was one of the strongest on record. The lowest lightning counts were observed in 2000, which had mostly cool or neutral phases of ENSO, including the lowest NIÑO 3.4 anomaly of the study period. W inter season lightning flash densities substantiates the role of ENSO in winter season lightning fluctuations. Enhanced CG flash regions and high correlation values (> 0.8) arranged in banded swaths indicate a southerly shift in frontal tracks during warm ENSO events. The lowest winter flash densities are associated with cool ENSO phases. 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, which is indicative of more lightning during La Niña summers. Although eight years is inadequate to establish a long-term pattern, results imply that the ENSO influences lightning across the US Gulf Coast.

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