Differences in the Formation and Evolution of the Inner Rainbands during the Rapid Intensification of Typhoon Cempaka (2021)

The organization and propagation of inner rainbands of landfalling Typhoon Cempaka (2021) during rapid intensification (RI) are investigated from two ground-based Doppler radars. Dual-Doppler analysis based on ground-based radars provide long-lasting high temporal and spatial three dimensional wind fields to examine the possible mechanisms for the organization of inner rainbands. In the early period when the convections were preferentially located inside the RMW, deformation plays an important role in the formation of inner rainbands. Convective cells were advected by the cyclonically rotating tropical cyclone swirling flow while being deformed into spiral shapes. In the later period when the convections were preferentially located outside the RMW, positive part of wavenumber-2 reflectivity associated with the rainband is collocated with the positive component of wavenumber-2 vorticity. The wavenumber-2 reflectivity moved at an azimuthal phase speed of 64.5% of the local tangential wind and very close to the theoretically predicted speed. It is evident that vortex Rossby wave is associated with the organization of rainband in the later stage.