Helicity: A Possible Indicator of Negative Feedback Initiation of Tropical Cyclone–Ocean Interaction

Abstract

Abstract The development of large‐scale vortex dynamo during tropical cyclogenesis through the mutual intensification of primary and secondary circulation in terms of helical evolution is well studied. However, the influence of atmospheric helicity on ocean surface heat and moisture fluxes associated with tropical cyclone (TC) evolution is yet to be understood. At its development stage, the heat and moisture flux from the ocean surface increases with the increase in intensity of the TC. This time, TC‐Ocean interaction works in a positive feedback mechanism. However, after a particular stage, the very intense wind of the TC causes strong turbulent mixing in the underlying ocean. Hence, the upper ocean layer temperature starts decreasing, leading to a decrease in heat and moisture flux exchange to the TC. We have analyzed the emergence of vortex helical structure in TC and the role of helicity in modulating surface heat and moisture fluxes. The result shows that helical development is associated with the axisymetrization of the vertical velocity and diabatic heating at the middle and upper troposphere. There is no definite TC intensity at which the initiation of negative feedback of TC‐upper ocean interaction occurs. However, the increase in helicity above 200 × 10−2 ms−2 reversed the TC‐ocean interaction trend. Therefore, TC helicity evolution and upper ocean interaction are essential to understand TC evolution.

Keywords

• tropical cyclones
• vorticity
• helicity
• ocean‐atmosphere interaction
• heat flux
• moisture flux