Interaction Between Inner and Outer Rainbands May Lead to a Second Rapid Intensification in Idealized Tropical Cyclone Simulations

Abstract

In the lifetime of a tropical cyclone (TC), there can be multiple rapid intensification (RI) periods. In idealized numerical studies of TCs, a two-stage mode of RI is frequently observed. However, the underlying mechanisms driving this phenomenon remain unclear. This study examines the physics of the second RI phase from the perspective of TC internal dynamics. It is revealed that the formation and maintenance of outer rainbands inhibit the development of inner rainbands, resulting in a more upright and compact heating structure within the inner core of the TC. This change in heating structure results in an intensification and inward movement of negative heating gradient that effectively enhances the boundary layer (BL) inflow within the radius of maximum wind (RMW), leading to a rapid increase in the inward flux of vorticity and ultimately contributing to the second phase of RI. This study highlights the significance of rainband interactions in the two-stage RI process of TCs, suggesting that enhancing our understanding and characterization of rainband interactions hold promise for key progress in TC intensity estimation and prediction.