Analysis of global Terrestrial Gamma Ray Flashes distribution and special focus on AGILE detections over South America

TL;DR

This study analyzes the global distribution of Terrestrial Gamma-ray Flashes (TGFs) detected by AGILE and RHESSI, highlighting regional differences, meteorological conditions, and the importance of storm activity and atmospheric parameters for TGF occurrence.

Contribution

It provides a detailed analysis of TGF distribution and meteorological conditions over South America, with new insights into regional differences and the influence of storm characteristics on TGF production.

Findings

TGF occurrence follows ITCZ seasonal migration and peaks in the afternoon.

High CAPE, cloud top altitude, and thunderstorm activity are associated with TGF production.

AGILE's exposure to active storms averages 68 hours per TGF detection.

Abstract

Global distribution of the Terrestrial Gamma-ray Flashes (TGFs) detected by AGILE and RHESSI for the period from March 2009 to July 2012 has been analysed. A fourth TGF production region has been distinguished over the Pacific. It is confirmed that TGF occurrence follows the Intertropical Convergence Zone(ITCZ) seasonal migration and prefers afternoons. TGF/lightning ratio appears to be lower over America than other regions suggesting that meteorological regional differences are important for the TGF production. Diurnal cycle of TGFs peaks in the afternoon suggesting that Convective Available Potential Energy (CAPE) and convection are important for TGF production. Moreover all AGILE passages over South America in the same period have been analysed to find meteorological preferences for TGF occurrence. In each passage the analysis of Cloud Top Altitude (CTA), CAPE, number of strokes, number of storms and coverage area of clouds with temperatures below $-70\,^{\circ}{\rm C}$ (Cloud Top Coverage area, CTC) are computed. On average, AGILE has been exposed to 19,100 strokes between each TGF representing $\sim$68 hours of exposure over active storms. High CAPE values, high cloud tops and high stroke occurrence suggests that meteorological conditions conducive to vigorous and electrically active storms are important for TGF production. It is shown that a high number of thunderstorms is preferable for TGF production which may be explained by a greater chance of the presence of a thunderstorm in the best development stage for TGF production. High tropopause altitude seems to be important but not primordial for TGF production.