利用移动新一代天气雷达 (CINRAD/CCJ) 和长乐新一代天气雷达 (CINRAD/SA) 基数据, 采用地球坐标系下的双雷达三维风场反演技术, 重点分析了2007年8月18日凌晨超强台风 “圣帕” 外围强带状回波的风场特征。结果表明, 带状回波具有以下特征: (1) 强盛阶段, 每个强回波中心在前进方向的右侧或右后侧对应于强东偏北风速中心 (强风核), 其中最强回波中心前侧还存在弱风速中心。这样的水平风场结构从低层一直保持到中层, 使得强回波区对应于水平辐合和正涡度区, 产生明显的上升运动, 有助于对流的发展和维持。强盛阶段云体快速移动。相对于移动的云体来说, 前侧及后侧中低层气流均指向强回波, 在强回波区及后侧水平辐合形成上升气流, 最大上升速度出现在强回波中心与北侧强风核之间。同时在强回波上空高层出现辐散, 气流主要向后流出。 (2) 减弱阶段, 较强回波中心或其北侧对应于弱风速中心, 回波中心出现负涡度区。云体移速变慢。相对于移动的云体来说, 偏东气流穿过云体。回波区气流辐合较弱, 明显的上升区出现在中层较强回波近台风中心一侧。(3) 强风核可以将位于带状回波前进方向后侧的处于减弱阶段螺旋云带的动量和水汽向带状回波发展区输送, 因此, 强风核结构很可能是带状回波快速发展的主要原因。
Based on the dual-Doppler radar data of the mobile weather radar (CINRAD/CCJ) and Changle weather radar (CINRAD/SA), the characteristics of three-dimensional wind structure in the puissant and weakening phases of the strong banded echo of super typhoon Sepat (0709) on 18 August 2007 are examined by means of dual-Doppler radar retrieval in the Earth coordinate. The results reveal that: 1) During the puissant phase, there were strong east by north wind centers (strong wind core ) along the right or the back of the right side of strong echoes in their course, even weak wind center existed in the front of the strongest echo. The structure maintained from the lower layer to the mid-layer, thus the strong echoes corresponded to the horizontal convergence and positive vorticity, resulting in significantly upward movement which helped the development and maintenance of convection. And the clouds migrated quickly. Relative to the moving clouds, the anterior and posterior air in the mid－lower layer flowed to the strong echoes, and then converged and ascended with maximum vertical velocity between strong echo center and the wind core on its northern side. In the meanwhile, divergence appeared in the higher layer over the strong echo area, and the air mainly flowed out backward. 2) During the weakening period, the weak wind center was located at the strong echo center or its north side with negative vorticity. The clouds moved slowly and the easterlies went through the clouds. The convergence over the echo area weakened and the obvious updraft appeared in the mid-layer strong echo near the typhoon center. Thus the banded echo has been difficult to maintain. 3) Strong wind core could transport the momentum and water vapor of weakening spiral cloud bands on the posterior side to the developing area of the banded echo; therefore the strong wind core structure was likely to be the main cause for the rapid development of banded echo.