Insights into Volcano Ash Plumes from Space-Born Passive Microwave Imagery

Explosive volcanic eruptions are among the most significant and devastating natural hazards on Earth. During an explosive eruption, a volcano can inject clouds of hot rocks, particles, and ash into the atmosphere. This ejected material can rise, spread, and then produce fallout of ash particles that can impact far-reaching and surrounding communities. While airborne in the stratosphere, volcanic particles can be a source of dramatic changes in global weather/climate patterns by affecting Earth’s radiative budget. Therefore, it is important to monitor volcanoes to better understand and more accurately model the associated atmospheric effects of their explosive eruptions.

Currently, there are various satellite remote sensors observing volcanic plume emissions and these are primarily in the infrared, visible frequencies as well as LiDAR. However, when volcanic ash plumes are obstructed by cloud formations, these sensors are unable to retrieve information beneath the additional layer and into the ash plume. However, often these clouds are semi-transparent to passive microwave (PMW) observations, resulting in detectable eruptions underneath the meteorological clouds. By utilizing the Global Precipitation Measurement Intercalibration dataset, we demonstrate the value of PMW observations during the 2022 Hunga Tonga eruption, 2021 Fukutoku Oka-no-Ba eruption, and other eruptions larger than a Volcanic Explosivity Index of 3. We find that space-born PMW radiometers observe sufficiently different signatures between meteorological convection and volcanic ash plumes. We derive a model relating ash optical thickness to the PMW signal over a frequency range of 18 GHz– 200 GHz explaining the observed differences in brightness temperatures.