Abstract
Two longitudinal-mode snowbands (bands I and II) were observed over the Ishikari Bay, Hokkaido, Japan during a wintertime cold-air outbreak. The three-dimensional kinematic structure of a snowband (band II) was examined in detail using dual-Doppler radar data. Band II noticeably developed over the Ishikari Bay. A high-reflectivity (approximately 35 dBZ at the maximum) zone was formed along the band axis and characterized the radar-echo structure of band II. The high-reflectivity zone of band II had the airflow structure dominated by circulations in vertical cross sections perpendicular to the band axis.
The interactions between the two snowbands were discussed. Interestingly, it was found that radarecho bridges existed at the low levels between the two snowbands. The radar-echo bridges were formed in association with low-level outflows from the meso-γ-scale convective cloud systems composing band I. The low-level outflows moved toward band II with time and penetrated into band II. This caused strong low-level convergence and the enhancement of updrafts in band II. Consequently, stronger radar-echoes were formed in band II and band II rapidly developed. Ice/snow particles were transported from band I into band II by the low-level outflows. It was considered that the rapid growth of these particles in the enhanced updrafts in band II would have contributed to the rapid development of band II.
