17:15 〜 19:15
[AAS02-P04] Diagnosing TC intensity variations through the lens of eyewall convective mass fluxes: a perspective from realistic simulations.
キーワード：Intensity variations, Tropical Cyclone, Internal Dynamics, Regional Simulations
Designing a conceptual model for TC internal dynamics is a crucial step towards a better understanding of their intensity changes. In the classical vortex spinup model, the spin up of the maximum tangential winds in an azimuthally-averaged vortex is determined by the radial convergence of absolute angular momentum above the boundary layer. Consequently, the ability of a TC to intensify requires the cooperative interaction between the eyewall convective mass flux that draws momentum surfaces inwards above the boundary layer, and the frictionally-induced inflow that brings the moisture flux that helps maintain the convective instability in the core region.
Using realistic, high-resolution WRF numerical simulations, this work assesses the connection between the boundary layer and eyewall mass fluxes, and the intensity changes of tropical cyclones. An in-depth analysis of a two-weeks long simulation of Hurricane Irma (2017) breaks down the main aspects of this interaction. In a broad perspective, intensification occurs when the boundary layer inflow increases and is met with a concurrently increasing upward mass flux in the eyewall, while maturity and decay go with the gradual decline of this eyewall mass flux, and the subsequent generation of outflow above the boundary layer near the eyewall. Diagnostic variables are designed to quantify the upward mass flux coming out of the boundary layer, and the amount of this mass flux successfully ventilated to the upper troposphere by the eyewall convection. The intensity change of simulated tropical cyclones is shown to concur for a major part with the joint evolution of these two quantities. The average convergence or divergence of the azimuthal-mean flow above the boundary layer does not, in itself, capture the spin up or spin down of tangential winds. Vortex intensification is rather associated with an increasing convergence in the boundary layer going with a net inflow above it, while intensity decay goes with the opposite.
This study highlights the importance of considering the eyewall convection along with boundary layer dynamics to diagnose the intensity variations of tropical cyclones.
Using realistic, high-resolution WRF numerical simulations, this work assesses the connection between the boundary layer and eyewall mass fluxes, and the intensity changes of tropical cyclones. An in-depth analysis of a two-weeks long simulation of Hurricane Irma (2017) breaks down the main aspects of this interaction. In a broad perspective, intensification occurs when the boundary layer inflow increases and is met with a concurrently increasing upward mass flux in the eyewall, while maturity and decay go with the gradual decline of this eyewall mass flux, and the subsequent generation of outflow above the boundary layer near the eyewall. Diagnostic variables are designed to quantify the upward mass flux coming out of the boundary layer, and the amount of this mass flux successfully ventilated to the upper troposphere by the eyewall convection. The intensity change of simulated tropical cyclones is shown to concur for a major part with the joint evolution of these two quantities. The average convergence or divergence of the azimuthal-mean flow above the boundary layer does not, in itself, capture the spin up or spin down of tangential winds. Vortex intensification is rather associated with an increasing convergence in the boundary layer going with a net inflow above it, while intensity decay goes with the opposite.
This study highlights the importance of considering the eyewall convection along with boundary layer dynamics to diagnose the intensity variations of tropical cyclones.