Journal Article

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

Buehler, Stefan A., Liu, Mengqi, Sepúlveda, Ignacio, Horváth, Ákos, Adams, David K., Sakradzija, Mirjana

2025

Overview

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. Plain Language Summary The giant Hunga volcano explosion on 15 January 2022 produced a special atmospheric wave, called the Lamb wave, that traveled around the globe somewhat faster than a jetliner. The Lamb wave increased the atmospheric pressure, slightly warming the air. Geostationary time loop imagery recorded the movement of this wave over the Gulf of Mexico, the Caribbean, and the North Atlantic Ocean during daytime hours. The observations reveal that the passing Lamb wave turned low‐level clouds momentarily darker. We argue that the cloud darkening is caused by the shrinkage of droplets inside and near clouds due to the warming. Key Points The Hunga Lamb wave caused detectable brightness variations in low‐level clouds 12,000 km away The dominant signal is a temporary darkening accompanying the peak overpressure We hypothesize the darkening results from the shrinkage of drops due to a sudden increase in temperature and decrease in relative humidity

• Publisher: John Wiley & Sons, Inc
• Subject: Atmospheric pressure / atmospheric waves / cloud adjustment / cloud darkening / Cloud droplets / cloud transition zone / Clouds / Darkening / Evaporation / GOES satellites / Hygroscopic particles / lamb wave / Lamb waves / Optical thickness / Overpressure / Reflectance / Relative humidity / Volcanoes