Structure and Evolution of Misovortices Observed within a Convective Snowband in the Japan Sea Coastal Region during a Cold-Air Outbreak on 31 December 2007

Abstract

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.

Doppler Radar Observations of a Wintertime Anticyclonic Misocyclone Associated with Surface Wind Gust on the Coast of the Sea of Japan

“…Among those studies, Kobayashi et al (2007) documented a radar-observed misocyclone within a parent cloud over the Sea of Japan and a visible waterspout funnel cloud connected to its cloud base. Inoue et al (2011), Inoue et al (2016), and Onomura et al (2017) pointed out that misocyclones have been associated with wind gusts which were confirmed by damage surveys and/or surface wind observations. Kusunoki et al (2017) investigated the vertical structure of a landfalling misocyclone at about 100-1000 m above the surface.…”

“…Recent observations with Doppler radars on the Sea of Japan revealed the existence of circulations aloft that were associated with wind gusts or waterspouts in winter (Kobayashi et al 2007;Inoue et al 2011;Inoue et al 2016;Kusunoki et al 2017;Onomura et al 2017). The circulations in those studies were referred to as misocyclones since their dimensions were less than 4 km (i.e., circulations with a diameter between 40 m and 4 km; Fujita 1981).…”