Revisiting oceanic elves and lightning occurrence rate during El Niño and La Niña episodes over a 10-year time frame

Abstract

The Sprite and Upper Atmospheric Lightning Imager (ISUAL) on board the Taiwanese satellite Formosat-2 accomplished its first decade operating in orbit. A comprehensive method defining the standardized elve anomaly occurrence rate using limb-viewed observation is demonstrated. We revisit the occurrence of elves during El Niño and La Niña and extend the time series analysis to November 2015. The variation in the enhanced elve anomalies occurrence density (AEOD) follows the change in sea surface temperature anomaly (SSTA) in the SSTA-Horseshoe, SSTA-Pacific, and SSTA-Indian Ocean during the warm and cold phases. However, the variation in lightning flash density anomalies (ALFD) is rather ambiguous. The Southern Oscillation Index (SOI) correlation with the Elve Anomaly Index (EAI) remains significant in Tahiti, while the best correlation between SOI and elves is found in the western/central Pacific Ocean with a correlation coefficient as high as 0.7. In the Indian Ocean the 10-year time frame correlation is moderate, but the relation is obvious during the transition phase between a strong El Niño following La Niña in the region where the synoptic circulation is affected. The weaker convection available potential energy (CAPE) in the upwelling synoptic circulation region provides an environment conducive to the development of elve-producing thunderstorms. This work substantiates the relation between elves/lightning and ENSO in a longer10-year time frame in which elves are more sensitive than lightning to ENSO and the variation in the synoptic circulation.