Further Numerical Study on the Formation of the Convergent Cloud Band over the Japan Sea in Winter

Abstract

Further numerical experiments are performed to supplement the numerical study of Nagata et al. (1986) on the formation of the convergent cloud band (CCB) over the Japan Sea in winter. The purposes are to evaluate the relative contributions of the three lower boundary forcings (the landsea thermal contrast, the blocking effect of the mesoscale mountains, and the characteristic SST distribution) to the formation of the CCB, and to investigate how the mountains north of the Korea Peninsula produce the low-level convergence zone.
Simulated mesoscale fields show that the contributions of each lower boundary forcing to the formation of the CCB are comparable. Convective heating is less important than sensible heating over the northwestern part of the Japan Sea in contrast with over the southern part. We make cross-section analyses and examine horizontal inertial stability of the CCB over the northwestern part of the Japan Sea. The dynamical effect of the mountains is shown to produce a local baroclinic environment, including a zone of near neutrality both to inertial and gravitational stabilities. Surface sensible heating appears to maintain the CCB in this zone. These findings suggest that the CCB is a mesoscale longitudinal roll parallel to the vertical shear vector associated with the local baroclinity.