On the rapid intensification of Hurricane Wilma (2005). Part IV: Inner‐core dynamics during the steady radius of maximum wind stage

Abstract

Recent studies show that some hurricanes may undergo rapid intensification (RI) without contracting the radius of maximum wind (RMW). A cloud‐resolving mesoscale model prediction of Hurricane Wilma (2005) is used herein to examine what controls the RMW contraction and how a hurricane could undergo RI without contraction. Results show that the processes controlling the RMW contraction are different within and above the planetary boundary layer (PBL). In the PBL, radial inflow contributes to contraction, whereas frictional dissipation acts as an inhibiting factor. Above the PBL, radial outflow and vertical motion are the two main factors governing the RMW contraction, with the former inhibiting it. A budget analysis of absolute angular momentum (AAM) shows that the radial AAM flux convergence is the major process accounting for the spin‐up of the maximum rotation in the PBL as the RMW contracts, while the vertical flux divergence of AAM and the friction oppose the spin‐up. During the RI stage with no RMW contraction, the local AAM tendencies in the eyewall are however smaller in magnitude and narrower in width than those during the contracting RI stage. In addition, the AAM following the time‐dependent RMW decreases with time in the PBL and remains nearly constant aloft during the contracting stage, whereas it increases during the non‐contracting stage. These results reveal different constraints for the RMW contraction and RI, and help explain why a hurricane vortex can still intensify after the RMW ceases contraction.

A Three-Dimensional Trajectory Model with Advection Correction for Tropical Cyclones: Algorithm Description and Tests for Accuracy

“…15d,h,l). Previous TC AAM budgets using azimuthally averaged variables have found friction and turbulence forcing to be small above the MBL (Zhang et al 2001;Qin et al 2018). Our results suggest that the 3D AAM material conservation assumption used for the Gal-Chen-based U r and V solver was reasonable for this CB.…”

“…is nearly conserved following the flow above the maritime boundary layer (MBL), where friction and diffusion may be neglected (Zhang et al 2001;Montgomery and Smith 2014;Qin et al 2018). Here we invoke the additional assumption that the pressure torque ›p/›l (Zhang et al 2001) is small enough such that AAM can be treated as a ''quasi-conserved'' variable following 3D flows over sufficiently short time intervals:…”

Relationship Between Size and Intensity in North Atlantic Tropical Cyclones With Steady Radii of Maximum Wind

“…The relationship between the intensity and R34 at a constant RMW can be described from a perspective of convection by using the tangential wind tendency equation as in previous studies (Fudeyasu & Wang, 2011; Qin et al., 2018; Li et al., 2019). The equation can be written: $$$\frac{\partial \bar{\mathrm{v}}}{\partial \mathrm{t}}=-\bar{\mathrm{u}}{\bar{\xi }}_{\mathrm{a}}-\bar{\mathrm{w}}\frac{\partial \bar{\mathrm{v}}}{\partial \mathrm{z}}-\bar{{\mathrm{u}}^{\prime }{{\xi }^{\prime }}_{\mathrm{a}}}-\bar{{\mathrm{w}}^{\prime }\frac{\partial {\mathrm{v}}^{\prime }}{\partial \mathrm{z}}}+{\bar{\mathrm{F}}}_{\text{sg}}$$$ …”

“…The weak correlation between the outer region size and intensity means that changes in the azimuthal‐mean tangential wind speed in the inner‐core region have generally been taken to be independent of the outer region (Smith et al., 2009; Weatherford & Gray, 1988). The relationship between TC size and intensity has usually been studied taking only the inner‐core size into consideration (Stern et al., 2015; Qin et al., 2018; Q. Wu & Ruan, 2021), or both the inner‐core and outer region sizes have been included but considered as constraints that affect subsequent variations in intensity (Carrasco et al., 2014; Xu & Wang, 2015, 2018). However, the intensity and outer region size have been found to be linearly related under certain conditions (Smith et al., 2010; Weatherford & Gray, 1988).…”

Active Role of Sea Surface Temperature Changes Over the Kuroshio in the Development of Distant Tropical Cyclones in Boreal Fall

“…Previous studies pointed out that the PBL inflow driven by eyewall latent heating played an important role in the development of a supergradient wind through the radial absolute angular momentum (AAM) advection (e.g., F20b; Kepert, 2001; Qin et al., 2018; Smith et al., 2009). We next show the magnified views of the azimuthal‐mean , the radial wind speeds, and the inward AAM advection below a 1 km height in Figures 7k–7o.…”