A dual-Doppler radar study of longitudinal-mode snowbands part II: Influence of the kinematics of a longitudinal-mode snowband on the development of an adjacent snowband

Two longitudinal-mode snowbands (bands I and II) were observed over the Ish ikari Bay, Hokkaido, Japan during a wintertime cold-air outbreak. The three -dimensional kinematic structure of a snowband (band II) was examined in de tail using dual-Doppler radar data. Band II noticeably developed over the I shikari 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, i t was found that radar-echo bridges existed at the low levels between the t wo snowbands. The radar-echo bridges were formed in association with low-le vel outflows from the meso-gamma-scale convective cloud systems composing b and 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 wo uld have contributed to the rapid development of band II.