Strongly Negative ZDR Signatures in Low Levels of Deep Convection

Differential Reflectivity (ZDR) is the log of the ratio of the horizontal power return to the vertical power return in dual polarization radars where positive values indicate horizontally oriented hydrometeors (e.g. large raindrops), and negative values indicate vertically-oriented hydrometeors (e.g. certain ice crystal habits). Most operationally useful ZDR signatures occur in precipitation regions with moderate to high radar reflectivity, but in some cases, unique patterns of strongly negative ZDR have been observed in low-level weak reflectivity regions of deep convection. These coherent patterns have been well sampled at multiple elevation angles, and they persist for multiple volume scans. The size, spatial continuity, and temporal continuity are unlike noise typically observed in areas of weak reflectivity and low signal to noise ratio. In this study we document the spatial and temporal characteristics of this unique radar signature, and in one case we compare with visual observations. The results can be useful in furthering our understanding of dual polarization radar data and in effectively analyzing ZDR in operational decision making.