The Importance of Horizontal Rolls in the Rapid Intensification of Tropical Cyclones

Abstract

The present laboratory study is focused on the role of convective rolls in the enhancement of the heat flux from the sea and triggering of the process of rapid intensification of tropical cyclones. The appearance of coherent convective structures such as thermals and rolls is registered by different optical techniques and temperature measurements. Two-dimensional velocity fields are used for the investigation of the structure and characteristics of the flow. The heat flux from the heating plate to the fluid is measured directly. Obtained results clearly show that rapid intensification of a laboratory analog of a tropical cyclone is tightly linked with the heat transfer process in the boundary layer. Formation of secondary convective structures strongly increases the heat transfer and intensity of convective circulations. The intensity of radial inflow is a crucial aspect for the intensification of cyclonic vortex, hence rapid variation of the heat transfer is a factor that has a substantial influence on the dynamics of a laboratory vortex. Time series of maximal radial and azimuthal velocities are in a good qualitative agreement with those from a theoretical model. It is shown that the mean square of the velocity depends linearly on the temperature difference between the inflow and the heating surface.