Doppler Radar Observation of Convergence Band Cloud Formed on the West Coast of Hokkaido Island. II: Cold Frontal Type

Abstract

A convergence band cloud moved southwestward through the Ishikari Plain on 20 January, 1986. In this study, we mainly used a single Doppler radar to examine the kinematic and radar echo structures of a convergence band cloud of the cold frontal type. The band cloud, approximately 40km in width, shifted southwestward and accompanied an advancing land-breeze front. The front was geometrically and dynamically similar to that of a gravity current found in laboratory experiments. Kelvin-Helmholtz instability waves with wavelength of 1-2km were observed along the interface of the land breeze and the northwesterly monsoon wind. Two small (*6km) vertical circulations similar to those seen in the warm frontal type were embedded in the mesoscale (*15km) vertical circulation. A low-level convergence and a resultant updraft which were stronger than that of the warm frontal type were located ahead of the front. A distinct subsidence, which is not found in the warm frontal type, followed the front. The updraft caused strong convective echoes ahead of the front, while, owing to the subsidence, the echoes behind the front rapidly weakened. The height of maximum updraft coincided with that of the potential instability layer. The updraft and the potential instability may be responsible for the formation of the convergence band cloud. Based on our observations, we constructed a conceptual model of the formation of the convergence band cloud.

Mesoscale Cyclogenesis in Winter Monsoon Air Streams : Quasi-geostrophic Baroclinic Instability as a Mechanism of the Cyclogenesis off the West Coast of Hokkaido Island, Japan

“…The linear theory also predicts that there are the easterly component and cold advection in the north of the trough of Mode I and the westerly component and warm advection in the south. Tsuboki et al (1989) observed a significant shift of the surface wind and temperature drop with a passage of the convergence band cloud which was accompanied by a mesoscale cyclone. Harimaya (1970) showed the surface wind was northeasterly to the north of the mesoscale cyclone and northwesterly to the south.…”

“…Okabayashi and Satomi (1971) found that the mesoscale cyclone is generated along a discontinuous line of temperature which is formed between the radiationally cooled air over the land and the warmer over-sea air. Tsuboki et al (1989) observed a significant temperature drop associated with the passage of a convergence band cloud. These previous studies suggest that baroclinicity in the lower troposphere may be important in the genesis of the mesoscale cyclone.…”

“…The convergence band cloud is a distinctive characteristic feature of this mesoscale cyclone. Recently, Doppler radar observations revealed the radar echo and kinematic structures of the convergence band cloud accompanying a mesoscale cyclone (Fujiyoshi et al, 1988a(Fujiyoshi et al, , 1988bTsuboki et al, 1989). Kobayashi et al (1989) used radar to find a detailed structures of a convergence band cloud and a mesoscale vortex of several tens kilometers in diameter.…”

Statistical Characteristics of Graupel Precipitation over the Japan Islands

“…Mesoscale vortex-like disturbances were analyzed by Asai and Miura (1981), and mesoscale snow bands were observed with a doppler radar (Sakakibara et al, 1988;Ishihara et al, 1989;Tsuboki et al, 1989). Recently a polar low developed over the Japan Sea was described by and Nic1992, Meteorological Society of Japan nomiya and .…”

Radar Echo Characteristics of the Localized Heavy Snowfalls around Sapporo, Japan.

“…Doppler radar observation studies over the same area also have been carried out till the present (Tsuboki et al, 1989;Fujiyoshi et al, 1992Fujiyoshi et al, , 1998Kikuchi, 1993;Katsumata et al, 1998). And the aspect of the snow clouds including the three-dimensional airflow structures with an updraft and downdraft regions has been clarifying.…”