Observations of Periods in Stratiform Precipitation with and without a ZDR Peak around the -15C Region

Long term observations of stratiform precipitation with a scanning polarimetric S-band radar and a vertically pointing Doppler X-band radar have led to the detection of two families of signatures near the -15^oC region: a) an enhancement of Z_DR combined with a reduction in Doppler vertical velocity and b) no enhancement in Z_DR with a weak to no reduction in Doppler vertical velocity. Previous studies (e.g. Kennedy and Rutledge 2011; Andric et al. 2013; Bechini et al. 2013) have attributed this Z_DR enhancement to the dendritic growth of ice crystals based on the Bailey and Hallett (2009) habit diagram. While attempts to link signatures of Z_DR and velocity to microphysical, mechanical, both, or other sources have so far been in vain, we have observed differences in the signatures of growth and precipitation rates in the altitudes below. Incorporating in situ aircraft measurements taken during the 2012 GCPEx campaign over the CARE site near Egbert, Ontario may provide additional insight on the remaining uncertainties.