A Numerical Study on the Formation and Maintenance of a Long-Lived Rainband in Typhoon Longwang (2005)

摘要

A 14-hr long-lasting spiral rainband of landfalling Typhoon Longwang (2005) was investigated based on a high-resolution simulation using the Advanced Research version of the Weather Research and Forecasting model. This rainband was previously suggested to be triggered and maintained by vortex-Rossby wave (VRW) dynamics based on available observations. The simulation results in the present study further suggest that the rainband originated from a previously existing wavenumber-2 VRW. The wave amplified via a positive feedback between Ekman pumping and diabatic heating. The wavenumber-1 convective forcing induced by the deep-layer environmental vertical wind shear also contributed to the amplification of the rainband after its formation. Although both observations and simulation showed the long-lived (greater than 10 hr) rainband with leading stratiform precipitation, unlike in observations, the rainband in the simulation showed a transition from an inner rainband to an outer rainband when the simulated rainband moved beyond the VRW stagnation radius at about 140 km from the storm center. As a result, in the band's later stages, VRW dynamics could not contribute to the maintenance of the rainband. Instead, both cold-pool dynamics and vertical wind shear-induced wavenumber-1 convective forcing played key roles in the further maintenance of the rainband.