Dual‐polarization radar signatures in snowstorms: Role of snowflake aggregation

Abstract

Abstract In this article a potential role of snowflake growth by aggregation on formation of dual‐polarization radar signatures in winter storms is discussed. We advocate that the observed bands of increased values of specific differential phase ( K dp ) can be linked to the onset of aggregation. These bands are caused by high number concentrations of oblate relatively dense ice particles and take place in regions where an ice phase “seeder‐feeder” is active. On the other hand, the differential reflectivity ( Z dr ) bands, in absence of detectable K dp values, are observed in the areas where crystal growth is the dominating snow growth mechanism and ice particle number concentration is lower. This distinction in underlying processes explains why K dp and Z dr bands are not always observed at the same time. Furthermore, based on surface observations of snowflakes, it is determined that early aggregates, consisting of a small number of ice crystals, are oblate. These oblate particles could contribute to the reported dual‐polarization radar signatures in snow, especially to the K dp . This could help to explain why, where observed at the same type, K dp and Z dr bands do not match and the altitude of the peak value of K dp is usually lower than the Z dr one. It also means that dual‐polarization radar signatures of snowflakes may depend on a stage of aggregation.