Transient Darkening of Low‐Level Liquid Clouds by the 2022 Hunga Lamb Wave Observed in GOES‐R Imagery

Abstract The 15 January 2022 eruption of the Hunga volcano generated a Lamb wave, a global atmospheric pressure perturbation which propagates purely horizontally at the speed of sound. Far‐field observations of the daytime passage of the Lamb wave by the Geostationary Operational Environmental Satellite‐R (GOES‐R) series, revealed unexpected, synchronized variations in the solar reflectance of low‐level liquid clouds, the most prominent of which is a transient darkening accompanying the overpressure peak. We hypothesize that this darkening is mostly caused by the rapid thermodynamic adjustment of the cloudy environment to the slight, but spatially coherent, warming introduced by the pressure pulse. The corresponding reduction in relative humidity leads to the shrinkage and evaporation of small cloud droplets and hygroscopic particles in the halo region, which, in turn, temporarily reduces the optical thickness of the cloudy column.