2016 Volume 94 Issue 6 Pages 507-524
Cyclonic misovortices with a horizontal scale of 0.4-1.9 km embedded within a convective snowband were observed by two X-band Doppler radars in the Japan Sea coastal region on December 31, 2007, during a cold-air outbreak. All vortices initially developed offshore, subsequently making a landfall. The structure and temporal evolution of these vortices during the landfall were investigated using high-resolution data obtained from two X-band Doppler radars.
The studied vortices developed along a low-level convergence line characterized by cyclonic horizontal shear, suggesting that horizontal shearing instability was responsible for the initial development of the vortices. A detailed investigation was performed on a vortex that passed within a close range (‹ 10 km) of both radars and almost directly over two surface observation stations. As this vortex approached the coast, it extended upward with time and eventually reached a height greater than half of the echo-top height of the parent snowband. During the landfall, the vortex core diameter contracted markedly and its peak tangential velocity and vertical vorticity increased at lower altitudes. Such a temporal change of low-level vortex was associated with an intensification of low-level convergence around the vortex and the convergence line. These facts suggest that the stretching of the low-level vortex was responsible for the low-level vortex contraction and increase in peak tangential velocity and vertical vorticity during the landfall.
