Using Lightning Flashes to Image Thunderclouds

The optical energy emitted by lightning flashes interacts with the surrounding cloud medium through scattering and absorption. The optical signals recorded by space‐based lightning imagers describe a convolution of lightning flash energetics and radiative transfer effects in the intervening cloud layer. A thundercloud imaging technique is presented that characterizes cloud regions based on how they are illuminated by lightning. This technique models the spatial distribution of optical energy in radiant lightning pulses to determine whether and to what extent each illuminated cloud pixel behaves like a homogeneous planar cloud layer. A gridded product is constructed that differentiates flashes that illuminate convective cells from stratiform flashes with long horizontal channels and anvil flashes whose optical emissions reflect off of nearby cloud surfaces. Producing this imagery with a rolling 15‐min window allows us to visualize changes in convection with a rapid (20 s) update cycle. Plain Language Summary Space‐based lightning imagers like the Lightning Imaging Sensor (LIS) on the International Space Station and Geostationary Lightning Mapper on National Oceanic and Atmospheric Administration's Geostationary Operational Environmental Satellites measure lightning by recording the clouds lighting up during the flash. Every flash illuminates the clouds in a different way because storm clouds are usually not a homogeneous slab but instead have differing concentrations of rain and ice from one place to another. Because light interacts with these particles, dense clouds have higher probabilities for the light to be reflected away from the sensor, and they will appear darker. We use the fact that every cloud will modify the flash in a different way to describe the cloud regions from lightning measurements. We ask whether each cloud behaves more like an irregular convective cloud, a homogeneous slab, or a case of reflections/a break in the clouds/a long horizontal lightning emitter. We then use some basic modeling of the optical signals to produce an imagery product that answers this question by highlighting each of these scenarios. Key Points Lightning optical energies measured from orbit depend on the energetics of the flash and scattering in the cloud medium By modeling optical lightning signals and comparing with recorded pixel energies, cloud layer scattering effects can be revealed A method of using optical lightning data to image thunderclouds is presente