Meso-β-scale vortices developing along the Japan-sea polar-airmass convergence zone (JPCZ) cloud band: Numerical simulation

Abstract

A high-resolution (6.0-km grid at 36°N) one-way triple-nested hydrostatic numerical model successfully simulates meso-β-scale vortices developing along the Japan-Sea Polar-airmass Convergence Zone (JPCZ) cloud band. Simulated key features of the vortices include an “eye-like” structure with its diameter of several tens of kilometers and surrounding spiral bands of upward motion. The simulated vortices emerge first as bendings in a belt of concentrated positive vorticity on the order of 10−3 s−1 along the JPCZ. The bendings become increasingly sharp and eventually their troughs of the vorticity belt wrap round themselves to form meso-β-scale cyclones with a pressure deficit of 2-4 hPa accompanied by a dry eye and spiral bands of upward motion, within 4-8 hours. A warm core characterizes the eye and adjacent moist ascent. Not only agreement in spatial scale and time scale for growth between simple linear theory and the simulation, but energy conversion analysis of the simulated disturbance show barotropic shear instability for the dominant developing mechanism of the meso-β-scale vortices.