Novel Comparison of Pyrocumulonimbus Updrafts to Volcanic Eruptions and Supercell Thunderstorms Using Optical Flow Techniques

Abstract

Convective dynamics in a supercell thunderstorm, a volcanic eruption, and two pyrocumulonimbus (pyroCb) events are compared by computing cloud-top divergence (CTD) with an optical flow technique called Deepflow. Visible 0.64-μm imagery sequences from Geostationary Operational Environmental Satellites (GOES)-R series Advanced Baseline Imager (ABI) are used as input into the optical flow algorithm. CTD is computed after post-processing of the retrieved motions. Analysis is performed on specific image times, as well as the full time series of each case. Multiple CTD-based parameters, such as the maximum and the two-dimensional area exceeding a specified CTD threshold, are examined along with the optical flow-retrieved wind speed. CTD is shown to accurately and quantitatively represent the behavior and magnitude of different deep convective phenomena, including distinguishing between convective pulses within each individual event. CTD captures updraft intensification as well as differences in convective activity between two pyroCb events and individual updraft pulses occurring within a single pyroCb event. Finally, the characteristics of high-altitude smoke plumes injected by two separate pyroCb pulses are linked to CTD using ultraviolet aerosol index and satellite imagery. Optical flow-derived parameters can therefore be applied to individual pyroCbs in real-time, with potential to characterize pyroCb smoke source inputs for downstream smoke modeling applications and to facilitate future tools supporting air quality modeling and firefighting efforts.