Departures from Axisymmetric Balance Dynamics during Secondary Eyewall Formation

Abstract

Departures from axisymmetric balance dynamics are quantified during a case of secondary eyewall formation. The case occurred in a three-dimensional mesoscale convection-permitting numerical simulation of a tropical cyclone, integrated from an initial weak mesoscale vortex in an idealized quiescent environment. The simulation exhibits a canonical eyewall replacement cycle. Departures from balance dynamics are quantified by comparing the azimuthally averaged secondary circulation and corresponding tangential wind tendencies of the mesoscale integration with those diagnosed as the axisymmetric balanced response of a vortex subject to diabatic and tangential momentum forcing. Balance dynamics is defined here, following the tropical cyclone literature, as those processes that maintain a vortex in axisymmetric thermal wind balance.The dynamical and thermodynamical fields needed to characterize the background vortex for the SawyerEliassen inversion are obtained by azimuthally averaging the relevant quantities in the mesoscale integration and by computing their corresponding balanced fields. Substantial differences between azimuthal averages and their homologous balance-derived fields are found in the boundary layer. These differences illustrate the inappropriateness of the balance assumption in this region of the vortex (where the secondary eyewall tangential wind maximum emerges). Although the balance model does broadly capture the sense of the forced transverse (overturning) circulation, the balance model is shown to significantly underestimate the inflow in the boundary layer. This difference translates to unexpected qualitative differences in the tangential wind tendency. The main finding is that balance dynamics does not capture the tangential wind spinup during the simulated secondary eyewall formation event.

Revisiting the Relationship between Eyewall Contraction and Intensification

“…Consistent with Figs. This stands in contrast to several recent studies that have concluded that the boundary layer winds in tropical cyclones are spun up by friction Abarca andMontgomery 2013, 2014). 16 shows that the spinup of the tangential wind field is at most heights due almost entirely to diabatic heating.…”

“…Several recent papers (e.g., Smith et al 2009;Abarca andMontgomery 2013, 2014), have proposed that the spinup of the inner core of tropical cyclones is largely a result of frictionally driven inflow in the boundary layer as opposed to spinup occurring through a deep layer of heating-induced inflow. These studies argue that the inflow that is induced by friction is large enough such that the associated radial momentum advection outweighs the direct negative (spin down) effect of friction.…”

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.…”

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).…”