Hydrometeors of varying sizes have different fall speeds; for example, larger raindrops have greater fall speeds than smaller raindrops. The resultant differential sedimentation leads to differences in residence time in a sorting layer where drops can be advected by the storm-relative winds. The resulting size sorting has an effect on the polarimetric radar variables including specific differential phase KDP and differential reflectivity ZDR. This study uses a simple numerical model of raindrop size sorting to analyze and further elucidate the relationship between the storm-relative winds and the ZDR and KDP fields. Increased mean storm-relative winds lead to increased ZDR magnitudes and decreased KDP magnitudes. The separation distance between ZDR and KDP maxima is proportional to the magnitude of the mean storm-relative wind and the orientation of a vector from ZDR to KDP maxima is aligned with the mean storm-relative wind over the sorting layer. Further, it is shown that larger values of storm-relative helicity are associated with greater separation distances and separation orientations approaching orthogonal to the shear vector over the sorting layer.
All Science Journal Classification (ASJC) codes
- Atmospheric Science
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science