Microphysical Insights from Dual-Polarization Spectral Decomposition in Updraft Environments during the RELAMPAGO Campaign

This paper presents spectral polarimetric decomposition from I&Q radar samples in updraft environments. First, updrafts are identified using dual Doppler analysis and polarimetric signatures of updrafts such as Zdr columns. Subsequently, the power spectrum (sZ), differential spectrum (sZdr), and coherence spectrum (s𝞺hv) are computed from I&Q radar samples obtained from the identified updrafts. Practical considerations about the computation of the spectrum from I&Q radar samples in updraft are also presented. The spectral analysis revealed that bimodalities in the spectrum can be found in updraft conditions. Furthermore, the separation in the spectrum of different kinds of particles allows us to study the microphysics of each set of particles in a mixed-phase scenario.

The network of C-band radars deployed during the RELAMPAGO campaign in Argentina is used in this study. The Colorado State University (CSU) C-band Hydrological Instrument for Volumetric Observations (CHIVO) radar and the C-band Scanning ARM Precipitation Radar 2 (CSAPR-2) are used to perform dual Doppler analysis. The Dec. 14, 2018 case is analyzed. These two radars recorded a squall line between them during the Dec. 14 case, allowing the retrieval of the 3D wind field. In addition to the Doppler winds, CSU-CHIVO also recorded Range Height Indicator (RHI) scans in the direction where updrafts were identified, allowing vertical analysis of the storms. The I&Q time samples from CSU-CHIVO's RHIs are used to compute the polarimetric spectrum.

The sZ, sZdr, and s𝞺hv are computed for the updrafts identified in RHIs during this study case. The computation of spectra is particularly challenging in updrafts since, in these environments, there is more turbulence. As a result, the spectrum tends to broaden, and the noise floor to increase, making it challenging to separate signal from noise. Practical considerations from the signal processing perspective that help to compute a cleaner spectrum in updraft will be presented.

A vertical reconstruction of the polarimetric spectrum along updrafts was performed using the signal samples from RHIs. The spectral evolution of particles at different heights in the updrafts is presented. These analyses allow us to study the polarimetric signatures in the spectrum of mix-phase regions. The spectral analysis shows a bimodality in regions where the Doppler winds display a convergence of inflows, which indicates a mix of phases. The polarimetric spectral decomposition signatures in these mixed-phase regions will be also presented.