Doppler Radar Study on the Successive Development of Snowbands at a Convergence Line near the Coastal Region of Hokuriku District

Abstract

During the field experiment of winter mesoscale convective systems over the Sea of Japan in 2001 (WMO-01), several snowbands associated with a cold front developed remarkably at 10@30 km off the coast of Hokuriku district on 28 and 29 January 2001. Dual-Doppler radar analysis was made to investigate the mechanisms responsible for the successive development of the snowbands.Derived wind fields revealed that a mesoscale convergence line was formed between the prevailing westerly and shallow (@1 km depth), cold southwesterly winds that blew from inland toward Toyama bay. As the downshear-tilting convective cells in the snowbands approached the convergence line, they became almost upright and their height increased from 4 km to 6@7 km. The edge of the southwesterly cold air temporarily became indistinct because of the entrainment of the air into the convective cells that developed aloft. However, the subsequent advection of the cold southwesterly reestablished the convergence line, and enabled the successive development of following snowbands.

Statistical Analyses of Snowfall Distribution in the Niigata Area and its Relationship to the Wind Distribution

“…1) as well as in that of Niigata. In some case studies, it has been reported that the cold land breeze from the mountains plays a crucial role in the maintenance of snowbands off the coast of Hokuriku (Ishihara et al 1989;Ohigashi and Tsuboki 2005) and off the coast of the area between Niigata and Hokuriku (Yoshihara et al 2004;Eito et al 2005). Ookubo and Kurokawa (2000) suggested that the southwesterly wind deflected by the mountain range in Hokuriku formed a shear line with the northwesterly winter monsoon.…”

An Intensification Process of a Winter Broad Cloud Band on a Flank of the Mountain Region along the Japan-Sea Coast

“…Intensifications of preexisting precipitation echoes during cold-air outbreaks have also been shown in Tsuboki et al (1989) and Yoshihara et al (2004). The low-level convergence formed along mountain flanks enhances updraft associated with preexisting echoes.…”

“…The unbalanced flow was forced toward the left in the high-pressure region, which formed winds with a southerly component. Ookubo and Kurokawa (2000) and Yoshihara et al (2004) showed that flows deflected by mountains generated heavy snowfall or snowfall intensification during cold-air outbreaks. In their studies, surrounding winds were deflected toward the left in the upwind of mountains and made convergence with the nondeflected flow.…”

“…They indicated that the cold pool was caused by diabatic cooling from the sublimation of snow. Ookubo and Kurokawa (2000) and Yoshihara et al (2004) mentioned that winds were locally deflected by mountains. This deflection produced convergence with surrounding winds and intensified precipitation.…”

Numerical Simulation of the Quasi-Stationary Snowband Observed over the Southern Coastal Area of the Sea of Japan on 16 January 2001

“…During the WMO-01, bandshaped snowfall systems were frequently observed around the coastal region of the Hokuriku district. Yoshihara et al (2004) observed several migratory snowbands associated with a cold front on 28 and 29 January, 2001, by using a dual-Doppler radar system. They revealed that a low-level mesoscale convergence line, which formed at 10-30 km offshore, con-tributed significantly to the successive development of the snowbands.…”