Evaluation of the impact of moist convection on the development of asymmetric inner core instabilities in simulated tropical cyclones

Abstract

This paper examines the nature and consequences of inner core instabilities in several intense tropical cyclones (TCs) simulated with a cloud-resolving numerical model. The initial wave growth leading to polygonal eyewalls and mesovortices in each TC is shown to closely resemble that found in a dry nonconvective vortex with the same primary circulation. Such agreement is reasonable partly because the bulk of the cloudy eyewall updraft is outside the vorticity ring in which the instability occurs. An energetic analysis of the TC instability verifies that the symmetric secondary circulation contributes relatively little to the early growth of eddy kinetic energy. On a longer time scale, isentropic potential vorticity mixing triggered by the instability irreversibly reduces the maximum wind speed of the dry vortex. In the more realistically simulated TC, moist convection modulates the mixing and regenerates the broken vorticity ring. Eventually, the maximum wind speed of the TC and the local parameters that determine its theoretical magnitude return to within a few percent of their preinstability values. It is found that the time scale for wind speed restoration is sensitive to the surface drag coefficient. The long-term effects of inner core instability on precipitation are briefly addressed.

An improved moist‐convective rotating shallow‐water model and its application to instabilities of hurricane‐like vortices

“…However, they are sufficient to generate spiral cloud patterns, as we showed. The development of the instability of the eyewall proper at early stages (up to ≈40 f −1 ) is only weakly influenced by moist convection, in accordance with findings of Naylor and Shecter (). This can be seen from comparison of Figures a,b and from Figure .…”

“…Thus Schubert et al () obtained formation of polygonal eyewalls as a result of barotropic instability near the radius of maximum wind in a purely barotropic model, without gravity waves. A detailed analysis of instabilities of tropical cyclones was undertaken with a cloud‐resolving model by Naylor and Shecter (), who showed that the results of Schubert et al () gave a useful first approximation for the eyewall instabilities. Our linear stability analysis shows that vortex Rossby wave motions are coupled to inertia‐gravity waves.…”

Forced, Balanced Model of Tropical Cyclone Intensification

“…5 and 6, because, at these times, the PV ring is narrow (0.85 < r 1 /r 2 < 0.89) and hollow (0.56 < P core /P eyewall < 0.75). For further discussion on these stability issues in more general dynamical settings, see Montgomery et al (2002), Nolan and Montgomery (2002), Rozoff et al (2009), Hendricks et al (2009, 2014, Hendricks and Schubert (2010), Naylor andSchecter (2014), andWu et al (2016).…”

Estimation of the Tangential Winds and Asymmetric Structures in Typhoon Inner Core Region Using Himawari‐8

“…The results of the method can be used to visualize and quantify the asymmetric wind components as the deviations from the axisymmetric components, as shown in section 5. It has been suggested numerically that the asymmetric components such as mesovortices play the important roles to intensify TCs (e.g., Hendricks et al, 2009; Kossin & Schubert, 2001; Naylor & Schecter, 2014; Schubert et al, 1999). Observational studies have documented the presence of mesovortices in the TCs inner core region (e.g., Fletcher et al, 1961; Kossin et al, 2002; Kossin & Schubert, 2004; Muramatsu, 1986; Shimada & Horinouchi, 2018).…”