The role of outer rainband convection in governing the eyewall replacement cycle in numerical simulations of tropical cyclones

Abstract

Eyewall replacement cycles (ERCs) are frequently observed during the evolution of intensifying tropical cyclones (TCs). Although intensely studied in recent years, the underlying mechanisms of ERCs are still not well understood, and a timely accurate forecast of ERCs remains to be a challenge. To advance our understanding of ERCs and provide insights into the improvement of numerical forecast of ERCs, a series of three-dimensional full physics simulations is performed using the Weather Research and Forecasting (WRF) model to investigate ERCs in TC-like vortices on an f plane. The simulated ERC in the control experiment possesses key features similar to those observed in real TCs including the formation and development of a secondary tangential wind maximum associated with the outer eyewall. The Sawyer-Eliassen diagnoses and tangential momentum budget analyses are performed to investigate the mechanisms underlying the secondary eyewall formation (SEF) and ERC. The simulations show the crucial roles of outer rainband heating in governing the formation and development of the secondary tangential wind maximum and demonstrate that the outer rainband convection must reach a critical strength relative to the eyewall convection before SEF and ERC can occur. The diagnoses reveal a positive feedback among low-level convection, acceleration of tangential winds and convergence of radial flow in the upper boundary layer, and surface evaporation that leads to the development of outer rainband convection and formation of secondary eyewall, and a mechanism for the demise of inner eyewall that involves the interaction between the transverse circulations induced by eyewall and outer rainband convection.

Effects of Air‐Sea Interaction on the Eyewall Replacement Cycle of Typhoon Sinlaku (2008): Verification of Numerical Simulation

“…This theory suggests that the surface friction increases the inflow underneath the broadened swirling wind at the top of the BL, and the strong inflow promotes the local development of supergradient winds in the SEF region. The other mechanism is based on the balanced feedback of the diabatic heating (Abarca & Montgomery, 2014;Rozoff et al, 2012;Zhu & Zhu, 2014). If sufficient diabatic heating occurs outside the primary eyewall, the secondary eyewall is induced by mass convergence at the low-level BL (Moon & Nolan, 2010;Zhu & Zhu, 2014).…”

Impact of subgrid‐scale processes on eyewall replacement cycle of tropical cyclones in HWRF system

“…Recent studies on eyewall replacement cycles (ERCs) greatly advanced our understanding of this unique inner‐core structural change often occurring in intense tropical cyclones (TCs) [e.g., Houze et al ., ; Wu et al ., ; Rozoff et al ., ; Judt and Chen , ; Moon and Nolan , ; Fang and Zhang , ; Huang et al ., ; Abarca and Montgomery , , ; Kepert , ; Qiu and Tan , ; Wang et al ., ; Menelaou et al ., , ; Zhu and Zhu , , , hereafter ZZ14 and ZZ15]. Yet a timely accurate forecast of ERCs remains a challenge for numerical weather prediction.…”

Are Eyewall Replacement Cycles Governed Largely by Axisymmetric Balance Dynamics?

“…In this viewpoint, the inward contraction of an eyewall is a mechanism driven by differential diabatic heating, and friction plays an unimportant role. This viewpoint continues to prevail in the current literature, as exemplified by Zhu and Zhu (2014) and by Kepert (2013, his section 6), who writes ''Once the outer RMW [radius of maximum wind] and eyewall have formed, we expect that their subsequent evolution will be governed largely by the classic theory (Shapiro and Willoughby 1982). '' Our own survey of the literature suggests that the foregoing view of eyewall replacement dynamics is founded on axisymmetric balance dynamics reasoning with comparatively little quantitative testing.…”