Rapid Scan Visible Imagery from the Geostationary Lightning Mapper (GLM) at 2.5-Minute Intervals Monthly Weather Review

The Geostationary Lightning Mapper (GLM) is an instrument designed to continuously monitor lightning. It is on the GOES-16 and GOES-17 satellites, viewing much of the Western Hemisphere equatorward of 55°. Besides recording lightning-flash information, it transmits background visible-band images of its field of view every 2.5 min. The background images are not calibrated or geolocated, and they only have ~10-km grid spacing, but their 2.5-min sampling can potentially fill temporal gaps between full-disk imagery from the GOES satellites’ Advanced Baseline Imager. This paper applies an initial calibration and geolocation of the GLM background images and focuses on animations for two cases: a volcanic eruption in Guatemala and a severe thunderstorm complex in Argentina. Those locations typically have 10-min intervals between full-disk scans. Prior to April 2019, the interval was 15 min. Despite coarse horizontal resolution, the rapid updates from GLM background images appear to be useful in these cases. The 3 June 2018 eruption of Fuego Volcano appears in the GLM background imagery as an initial darkening of the pixels very near the volcano and then an outward expansion of the dark ash cloud. The GLM background imagery lacks horizontal textural detail but compensates for this lack with temporal detail. The ash cloud resembles a dark blob steadily expanding from frame to frame. Animation of the severe thunderstorm scene reveals vertical wind shear, with northerly low-level flow across a growing cumulus field and west-northwesterly upper-level flow at anvil level. Convective initiation is seen, as are propagating outflow boundaries and overshooting convective cloud tops. Grant no. NA19AANEG0136