Radar Detection of Electrified Cloud Areas

Polarimetric radars variables carry information on alignment of ice crystals in clouds that can be used to identify in-cloud electric fields. For that reasons the polarimetric variables obtained with radars in simultaneous transmission (SHV) and depolarization (DP) modes are analyzed. Fields of Z_DR, ρ_hv, and Φ_DP (SHV mode) and L_DR, ρ_xh, and Φ_xh (DP mode) show areas with strongly aligned ice particles in thunderstorms caused by in-cloud electric fields. Our experiments with relatively quick switching between SHV and DP modes showed certain advantages of the DP mode in detection of electrified areas. Typically, the DP mode exhibits larger areas of electric field influence in thunderstorms than those in the SHV mode. Advantages of the lag1 estimators of the polarimetric variables over the standard ones are also demonstrated.

Data from stratiform clouds have been also analyzed. The SHV mode in such cases does not indicate areas of aligned ice cloud particles, but these are observed in the DP mode. Physical reasons of such observations are discussed.

Lightning echoes have been captured during the experiment. Differences in the polarimetric variables of SHV and DP modes from lightning are presented. The Doppler spectra from lightning differ from those from raindrops and ice crystals that can be used to identify lightning echoes. Possible utilizations of the properties of electrified zones and lightning in SHV and DP modes are discussed for polarimetric phased array radar. Because on these radars the modes can be switched very fast we speculate that it might be possible to determine the onset of lightning.