A Possible Origin of Linear Depolarization Observed at Vertical Incidence in Rain

Recent observations by two different nadir pointing airborne radars with some linear polarization capabilities at times have detected surprisingly large linear ratios in convective tropical rain. This depolarization be explained if the rain is considered to be a mixture of a group of apparent spheres and another group of drops that are distorted in the horizontal plane perpendicular to the direction of propagation of the incident wave. If confirmed in future observations, this suggests that at times the shapes of a significant portion of the larger raindrops are disturbed apparently of collisions with smaller drops. Since many of the interpretations of radar polarization measurements in rain ground-based radars presume that the raindrops shapes correspond to those of the so-called `equilibrium' drops, the present observations may require adjustments to some radar polarization algorithms for estimating rainfall rate, for example, if the shape perturbations observed at nadir also apply t...