Dynamics and predictability of secondary eyewall formation in sheared tropical cyclones

Abstract

This study examines the predictability and dynamics of tropical cyclone (TC) secondary eyewall formation (SEF), eyewall replacement cycles (ERC), and intensity changes under moderate environmental shear through convection‐permitting ensemble simulations. Even with the same environmental shear, the TC intensity changes during formation, rapid intensification, and SEF/ERC can be extremely sensitive to small, unobservable, random initial condition uncertainties, or computer's truncation error due to the chaotic nature of moist convection. Through composite analysis of five ensemble members with similar clear SEF/ERC and diagnostics with a nonlinear boundary layer (BL) model, we identify several key factors in the SEF/ERC process: (1) fast expansion of outer wind fields and changing inertial stability through shear‐induced peripheral convection outside of the primary eyewall, (2) downward building and axisymmetrization of the primary (outer) rainband due to enhanced inertial stability and positive feedback between BL and outer convection, (3) establishment of the secondary eyewall along with moat formation that is facilitated by compensating subsidence from the primary eyewall, and (4) weakening and eventual replacement of the original primary eyewall by the strengthening secondary eyewall. It is also seen from the partial ERC cases that the preexisting rainband can be of great importance to the later development of SEF. Diagnosis with the nonlinear BL model shows that the location and relative strengths of the diagnosed frictional updrafts closely match those in the ensemble simulation of the ERC case, suggesting that the boundary layer convergence substantially influences the location of the convection in both eyewalls there.

Document Details

Document Type
Pub Defense Publication
Publication Date
Jan 22, 2017
Source ID
10.1002/2016ms000729

Entities

People

  • Dandan Tao
  • Fuqing Zhang
  • Jeffrey D. Kepert
  • Y. Qiang Sun

Organizations

  • Bureau of Meteorology
  • National Oceanic and Atmospheric Administration
  • National Science Foundation
  • Office of Naval Research
  • Pennsylvania State University

Tags

Readers

  • Atmospheric Science/Meteorology
  • Control Systems Engineering.
  • Ocean-Atmosphere Mesoscale Modeling, Data Assimilation, and Flux Boundary Layers