Tropical Cyclone Convection and Tropical Cyclogenesis

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The proposed project aims to improve our understanding of the processes by which tropical cyclones form. We know that deep convective clouds (thunderstorms) play an important role in the formation process, but the precise details of how these clouds operate to organize and intensify an incipient disturbance is not well understood. The role of moderately deep clouds in the formation of a cyclone is poorly understood as is the role of upper tropospheric ice clouds, which are a byproduct of deep convection. We know that both deep and moderately deep convective clouds locally amplify the rotation of an incipient disturbance, but we do not know precisely how important this rotation is for the formation of a tropical cyclone. We propose to address the foregoing gaps in knowledge by further analyses of idealized numerical model simulations of tropical cyclogenesis. These analyses will include an investigation of the structure and evolution of deep convective systems that develop in different regions of the simulated storms and the ability of these convective systems to induce lower tropospheric inflow, a known requirement for vortex intensification. We will investigate the role of ice clouds by comparing a simulation with ice processes included with one in which they are excluded.We plan also to examine the statistics of deep and moderately deep convective clouds during the formation of simulated storms and to relate the upward mass of air carried by the convection to the thermodynamical properties of the rising air as it leaves the near-surface friction layer, typically 1 km deep. Our recent work has shown that vortex intensification depends in a delicate way on the ability of deep convection to remove the air that is flowing towards the vortex centre within this friction layer.