强台风“山神”外围超级单体引发的龙卷分析

THE ANALYSIS OF TORNADO CAUSED BY SUPERCELL IN OUTER-BAND OF TYPHOON SHANSHEN

利用雷达、探空、自动站等资料及数值模拟对2012年10月南海强台风"山神"引发龙卷的外围雨带中超级单体的结构特征和环境场特征进行分析,结果表明:⑴超级单体既有大陆性超级单体特征(有弱回波区、强的回波悬垂和中气旋等),又有热带对流回波特征(回波质心高度和强的回波高度低);⑵当超级单体发展时,云内有较强的倾斜下沉气流,下沉气流向前流出有利于右后侧气流的流入,使得单体进一步发展,同时下沉气流使得云底高度下降,加大发生龙卷的概率;⑶龙卷发生前的环境场中层有干冷空气侵入,增加了大气不稳定度,同时低层具备较强的垂直风切变和低的抬升凝结高度的有利条件;⑷除地形摩擦辐合抬升有利于垂直涡度增加外,局地的三角洲地形也有利于局地垂直涡度增加,大大增加发生龙卷的概率。

Using data of radar, radiosonde and automatic weather stations and numerical simulation, this paper analyzes the structure and environment field of a supercell which caused tornado in the outer rain-belt of severe typhoon Shanshen in the South China Sea in October 2012. The result shows that in nature the supercell is both continental （having areas of weak echoes, strong echo pendency and mesocyclones） and tropical in convection echo （having lower strong echo height and lower echo centre of mass）. When the supercell developed, an inclined descending air current occurred in the cloud and flowed forward, favoring the inflow of air current from the right rear portion and making the cell develop further, and at the same time, the descending current dropped the height of cloud base, which increased the probability for the tornado to happen. The environment field prior to the occurrence of the tornado was intruded by dry and cold air, which increased the current instability, and the low level was with strong vertical wind shear and low level of uplift condensation that favored the tornado. Moreover, local delta terrain was in favor of the growth of local vertical vorticity and the increase of the probability of tornado, in addition to the convergent uplift due to topographic friction.