Can volcanic lightning be observed in space?
Monday, 15 December 2014
Lightning, a phenomenon widely known to occur in thunderstorms, is also present in major volcanic eruptions. Although volcanic lightning is not apparently different, its occurrence within ash clouds increase the difficulty to detect and measure it optically with remote instruments. Major volcanic eruptions, those with Volcanic Explosive Index (VEI) > 3 or with ash plume heights greater than 10 km are likely to have lightning. This lightning should be seen from space by LIS and OTD (Lightning Imaging Sensor, Optical Transient Detector). Ash clouds however absorb much more light than regular clouds which results in lower or no radiance measured for lightning in the ash plume. The LIS/OTD satellite data was studied for a small region centered on different volcanoes during reportedly active periods (3 days or more). This volcanic lightning should be distinguished from thunderstorm lightning according to specific criteria. All relevant eruptions that have occurred since LIS was launched in 1997 aboard TRMM (Tropical Rainfall Measurement Mission) Observatory need to be studied. LIS and OTD are in low orbits and do not cover the entire globe. Since any volcano is observed only a few minutes each day the likelihood of observing lightning events during a volcanic eruption is low. Inter comparison of lightning data from several eruptions, at different dates and places all over the world helps set a criteria to distinguish volcanic lightning from thunderstorm related lightning. LIS datasets, typically structured in four different levels – events,groups,flashes, areas – are plotted separately using conventional IDL algorithms to retrieve orbit data from individual HDF files. Events associated to volcanic lightning are distributed in fewer groups, which in turn are structured in less flashes than “regular” lightning.