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Abstract:
Although a strong tropical cyclone is often treated as an axisymmetric vortex in most theoretical studies, asymmetric structure always exists in the inner core of a TC in nature. The asymmetric structure in a TC vortex can be generated by either the internal dynamics or external environmental forcing, such as the environmental vertical wind shear (VWS). Previous studies have investigated how the environmental VWS may trigger the wavenumber-one asymmetric structure in an initially axisymmetric TC vortex and how the TC intensity changes under the influence of the imposed environmental VWS. In this study, the possible effect of the initial asymmetric structure in the TC vortex on the intensity change of a TC under the influence of an imposed environmental VWS is investigated based on idealized high-resolution full-physics model simulations. Results show that the effect of the initial asymmetric structure in the TC vortex can either enhance or suppress the initial weakening of the TC in response to an imposed moderate environmental VWS depending on the azimuthal phase of the initial asymmetric structure relative to the wavenumber-one asymmetric structure induced by the environmental VWS. When the initial asymmetric structure is in phase of the VWS-induced asymmetric structure, the TC weakening in response to the imposed VWS will be enhanced and vice versa. Our finding calls for attention to the realistic representation of TC asymmetric structure in the initial condition of numerical weather prediction models. Our finding also suggests efforts needed to improve observations to better resolve the asymmetric structure of TCs.
