Mesoscale Meteorological Structure Associated With Huge Band Echo

[摘要] Huge band echoes of 200 to 400km in width have been frequently observed by Mt. Fuji radar or by multi-radar echo composite. These band echoes are considered mesoscale system in the direction normal to them. The orientations of the band echoes are nearly WSW to ENE. The mesoscale meteorological structure associated with the band echoes is examined with routine radiosonde data. In order to extract the features common and essential to the band echo, the mean structure of various meteorological elements is prepared by superposing a large number of the cases. The following features are obtained from the mean vertical cross-section across the band echo.(1) Within the band echo of stratiform type, a slanting layer with large horizontal gradient of wet-bulb potential temperature (θw) is found in the lower and middle troposphere. Along this slanting layer, the vertical vorticity takes large values. The inclination of the layer is ca. 1/100, which is reasonable value for usual frontal surface.(2) Above this front-like layer, the updraft is found, the maximum value of which is several tens mb/hr and is located on the southside of the center line of band in the middle troposphere. In conformity with this, the intense echo zone is found also on the south of the center line. Below the front-like layer, the downdraft is present.(3) In the vertical cross-section of wind component parallel to the orientation of band echo, jet-like strong wind is situated in the central region of band echo at ca. 500mb, and extends slantwise toward lower levels to reach 700mb near the southern edge of band echo.(4) In the case of convective band echo, the front-like layer as seen from the distributions of θw and vertical vorticity is situated on the northside of the band echo, and the band echo seems to develop over the tongue of high θw in the lower troposphere. That is, the convective band echo is considered prefrontal in nature.(5) In the case of convective type, the wind component parallel to the band echo is fairly small, compared with the case of stratiform type.The above features will serve for understanding the mechanism of band echo and also for estimating the mesoscale meteorological field from the observed radar echo pattern in the data sparse area.

[学科分类] 大气科学