Midtropospheric Anticyclonic Vortex Street Associated with a Cloud Band near a Cold Front

Abstract

Abstract The characteristics and formation mechanism of an anticyclonic vortex street of meso-β scale, which appeared near a cold front around the Ryukyu Islands, Japan, on 11 April 1995, were examined by an analysis of observational data, a numerical simulation, and a linear stability theory. The vortex street was generated near the midtroposphere on the north edge of a cloud band along the cold front. The diameter of individual vortices was 70 km, and the interval between vortices was 100–200 km. The phase speed of the vortices was nearly equal to the wind speed at the 400-hPa level. The cloud band was accompanied by a weak wind region, in which the along-front wind was about 15 m s−1 weaker than that in the environment. A region of large anticyclonic horizontal shear (∼10−4 s−1) existed on the north side of this weak wind region. To examine a detailed structure and formation mechanism of the weak wind region, a numerical simulation was performed. Regions of active convection and convective cloud bands,...