台风云娜（2004）的高分辨率数值模拟研究:眼壁小尺度对流运动

通过对2004年云娜台风高分辨率模拟结果的分析,发现在环境垂直风切变不是单一方向情况下,中尺度涡旋只在对流层低层的眼壁区域形成.这些涡旋中有的伴随气旋环流是闭合的,有的则为非闭合;并且有的伴随着小尺度对流上升运动,而有的则没有.进一步分析发现当环境入流与涡旋的出流相遇产生辐合时,或者入流受涡旋本身阻挡产生辐合时,小尺度对流上升运动随即发生.中尺度涡旋伴随着对流上升活动在眼壁中沿气旋方向移动,表现出涡旋Rossby波特征,当移动至垂直风切变矢量下风向时对流加强,加强的上升气流通过拉伸涡管使得相麻的涡旋环流也加强,通常对流在移向垂直风切变矢量上风向时逐渐减弱.反观在眼壁区域的对流层中上层,没有明显的中尺度涡旋活动,强对流活动主要集中在眼壁东南侧,并且强上升运动也呈现小尺度特征.眼壁区域中速度大于1 m/s的上升运动仪占14%,大于2 m/s的则小于7%,但速度超过1 m/s的向上的质量通量约占整个上升运动的30%,表明尽管这些小尺度强对流运动所占空间比例较小,却在眼壁质量输送中起着重要作用.另外,这些强上升运动核表现出正的浮力特征,大值浮力分布与上升运动核位置一致的特征也进一步说明眼壁中大量的垂直质量通量输送与只占很小范围的小尺度上升运动有关.

A high resolution numerical simulation of T yphoon Rananim (2004): Small scale convection in the eyewall

In terms of the analysis of results of the high-resolution numerical simulation of Typhoon Rananim (2004), this study finds that the mesovortices form only in the lower troposphere in the eyewall in the presence of the non - unidirectional vertical shear. Both closed and unclosed circulations associated with these vortices are observed. In addition, some of the mesovortices are accompa-nied by small-scale updrafts, while no updrafts are found in other vortices. If the environmental inflow meets the outflow of the vortex circulations, or if the vortices themselves act as obstacles to prevent the inflow, small-scale updrafts associated with the mesovortices occur. The mesovortices and corresponding updrafts move cyclonically along the eyewall, characterized by the behavior of vortex Rossby waves. When travelling to the downshear direction, the convective updrafts strengthen, so that the associated mesovortices al-so become stronger by stretching the vorticity tubes. By contrast, the updrafts weaken as they progress to the upshear direction. In the middle and upper levels of the eyewall, there are no mesovortices and the strongest convection with the small-scale intense updrafts is concentrated on the southeastern side of the eyewall. The updrafts > 1 and 2 m/s occupy only 14% and 7% of the eyewall region, respectively. However, the updrafts >1 m/s contribute to 30% of the mass transport in the eyewall. This indicates that, although these small-scale intense updrafts occupy relative smaller areas in the eyewall, they play an important role in the mass transport in the eyewall. It is further found that the active updrafts may appear positively buoyant. In addition, the locations of the buoyancy of large magnitude are superposed with the strongest upward motions, further indicative of the significant role of the small-scale intense up-drafts.