Mobile Ka-Band Polarimetric Doppler Radar Observations Of Wildfire Smoke Plumes

Abstract

Remote sensing techniques have been more recently used to study and track wildfire smoke plume structure and evolution; however, knowledge gaps remain due to the limited availability of observational datasets aimed at understanding the fine-scale fire-atmosphere interactions and plume microphysics. In this study, we present a new mobile millimeter-wave (Ka-band) Doppler radar system acquired to sample the fine-scale kinematics and microphysical properties of active wildfire smoke plumes from both wildfires and large prescribed fires. Four field deployments were conducted in the fall of 2019 during two wildfires in California and one prescribed burn in Utah. An additional dataset of precipitation observations was obtained prior to the wildfire deployments to compare the Ka-band specific signatures of precipitation and wildfire smoke plumes. Radar parameters investigated in this study include reflectivity, radial velocity, Doppler spectrum width, Differential Reflectivity (ZDR), and copolarized correlation coefficients (HV). Observed radar reflectivity ranged between -15 and 20 dBZ in plume and radial velocity ranged 0 to 16 m s-1. Dual-polarimetric observations revealed that scattering sources within wildfire plumes are primarily nonspherical and oblate shaped targets as indicated by ZDR values measuring above 0 and HV values below 0.8 within the plume. Doppler spectrum width maxima were located near the updraft core location and were associated with radar reflectivity maxima.