The relation between prevailing precipitation-particle type and radar echo structure around the Dewa Hills

Abstract

Snow clouds influenced by topography were observed on 13–19 February 1992, and were analyzed using the data of Doppler radars, surface observations and rawinsondes. The analysis period was divided into two stages (stages I and II) based on the radar echo pattern and the rawinsonde data. The radar echo intensified over the Dewa Hills in both stages. Each stage represented the different type of snow cloud. The cloud type was clearly related to the prevailing precipitation-particle type. The cold outbreak was weak and widespread echoes appeared in stage I. Snowflakes were dominated among the observed precipitation-particles, and weak orographic lifting was expected. It is suggested that deposition growth prevailed over the Dewa Hills in stage I. The cold outbreak was strong and many echo cells were observed in stage II. Graupels dominated among the observed precipitation-particles. The low-level wind favored the strong orographic lifting. It is inferred that riming growth prevailed over the Dewa Hills in stage II. The contribution of graupel to the precipitation intensity was larger when the observation site was closer to the center of an echo cell.