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 fo rm only in the lower troposphere in the eyewall in the presence of the non-unidi rectional vertical shear. Both closed and unclosed circulations associated with these vortices are observed. In addition, some of the mesovortices are accompanied 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 updraft s associated with the mesovortices occur. The mesovortices and corresponding u pdrafts move cyclonically along the eyewall, characterized by the behavior of vo rtex Rossby waves. When travelling to the downshear direction, the convective up drafts strengthen, so that the associated mesovortices also become stronger by s tretching 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 u pdrafts 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. Th is 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 positive ly buoyant. In addition, the locations of the buoyancy of large magnitude are su perposed with the strongest upward motions, further indicative of the significant role of the small-scale intense updrafts.