High Temporal Resolution Observations of Cloud Electrification with Spectral Polarimetry

The signatures of ice crystal alignment in electrified clouds have been observed with polarimetric weather radar. Moreover, the evolution of the electric field build-up to discharge often requires radar observations with update time faster than the conventional weather radars can offer. Phased array radar can provide high-temporal resolution through electronic steering and digital beamforming (or imaging). The Advanced Radar Research Center (ARRC) at the University of Oklahoma (OU) has developed a S-band mobile polarimetric phased array radar called Horus, which exploits the all-digital architecture to provide maximum flexibility of scanning pattern and fast update time. Moreover, spectral polarimetry can provide microphysical and dynamical information within the radar resolution volume by estimating the polarimetric variables as a function of radial velocity. For example, polarimetric signatures of ice crystal and other hydrometeors like graupel and aggregates can be separated when size sorting is present. In this work, the observations of lightning process using Horus with fast update time (RHI scans every 8 s) will be reported. The signature of spectral polarimetric variables associated with lightning processes such as ice crystal alignment and direct microwave transmission will be discussed. In addition, other lightning events observed using the Rapid scan X-band Polarization (RaXPol) radar will be presented. Evident signatures of ice crystal alignment manifested by specific different phase in both time and spectral domains will be presented and discussed. Lightning mapping arrays map channel locations to ~30 ns and 10 m precision, and so can be co-located precisely with polarimetric radar data as fast as the radar can provide updates. Such correspondence was found with one lightning flash using the Oklahoma LMA and a polarimetric RHI every 5 s. One example is provided in the figure below.