An idealized numerical study of tropical cyclogenesis and evolution at the Equator

Abstract

Tropical cyclone formation and evolution at, or near, the Equator is explored using idealized three‐dimensional model simulations, starting from a prescribed, initial, weak counterclockwise rotating vortex in an otherwise quiescent, nonrotating environment. Three simulations are carried out in which the maximum tangential wind speed (5 m s −1) is specified at an initial radius of 50, 100, or 150 km. After a period of gestation lasting between 30 and 60 hr, the vortices intensify rapidly, the evolution being similar to that for vortices away from the Equator. In particular, the larger the initial vortex size, the longer the gestation period, the larger the maximum intensity attained, and the longer the vortex lifetime. Beyond a few days, the vortices decay as the cyclonic vorticity source provided by the initial vortex is depleted and negative vorticity surrounding the vortex core is drawn inwards by the convectively driven overturning circulation. In these negative vorticity regions, the flow is inertially/centrifugally unstable. The vortex evolution during the mature and decay phases differs from that in simulations away from the Equator, where inertially unstable regions are much more limited in area. Vortex decay in the simulations appears to be related intimately to the development of inertial instability, which is accompanied by an outward‐propagating band of deep convection. The degree to which this band of deep convection is realistic is unknown.

Evolution of convective characteristics during tropical cyclogenesis

“…As described in Kilroy et al . (2020), it is axisymmetric and warm‐cored with a maximum tangential wind speed of 5 m·s −1 at the surface. The initial temperature field is in thermal wind balance and is determined using the method described by Smith (2006).…”

Relationship between Early-Stage Features and Lifetime Maximum Intensity of Tropical Cyclones over the Western North Pacific

“…LMI might be affected by multiple factors during a TC's lifetime, including its genesis conditions. Previous studies on the physical mechanisms and favorable conditions of TC genesis have been conducted [9][10][11][12][13]. The genesis process of a TC can be divided into two consecutive stages [14,15]: first, from a tropical disturbance to a tropical depression (TD) with the formation of initial circulation; and second, from a tropical depression to a tropical storm (TS) when its warm-core structure is established.…”