Sensitivity of Optical-Flow-Retrieved Wind Speed and Cloud-Top Divergence of Convective Phenomena to Spectral and Temporal Input Conditions

Optical flow techniques have recently been used to retrieve cloud-top motion around convective updrafts and to compute divergent flow using visible imagery from passive remote sensing platforms, such as Geostationary Operational Environmental Satellite Advanced Baseline Imager (ABI). This study applies these novel methods to multiple convective phenomena, including a supercell thunderstorm, a tropical cyclone, a volcanic eruption, and multiple pyrocumulonimbus (pyroCb) events. Optical-flow-retrieved wind vectors and cloud-top divergence (CTD) are compared in order to provide quantitative context and test the baseline functionality of optical-flow-retrieved parameters as investigative tools for all types of deep convection. Multiple time steps between images, representing the different scan modes of ABI, are tested as input to determine the feasibility of using imager scans with larger spatial coverage, such as full-disk. Multiple spectral channels are also tested, spanning the range from visible to longwave infrared. Characterizing different channels as inputs is critical for the application of optical flow to a wider variety of situations, such as nighttime, oblique viewing angles, or semi-transparent cloudy conditions. Results suggest that retrievals of wind speed and CTD break down depending on the scan frequency and spectral channel used. However, when the retrievals break down is also dependent on other characteristics such as ambient wind speed. Optical flow-derived parameters can uniquely provide a top-down analysis of convective phenomena, including individual pyroCbs, in real-time, with potential for wide-ranging applications, such as characterize pyroCb smoke source inputs for downstream smoke modeling or tropical cyclone intensification studies. Knowing when these techniques can and can’t be applied is critical for their advancement in future applications.