Effects of parameterized boundary layer structure on hurricane rapid intensification in Shear

Jun A. Zhang, Robert F. Rogers

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

This study investigates the role of the parameterized boundary layer structure in hurricane intensity change using two retrospective HWRF forecasts of Hurricane Earl (2010) in which the vertical eddy diffusivity Km was modified during physics upgrades. Earl undergoes rapid intensification (RI) in the low-Km forecast as observed in nature, while it weakens briefly before resuming a slow intensification at the RI onset in the high-Km forecast. Angular momentum budget analysis suggests that Km modulates the convergence of angular momentum in the boundary layer, which is a key component of the hurricane spinup dynamics. Reducing Km in the boundary layer causes enhancement of both the inflow and convergence, which in turn leads to stronger and more symmetric deep convection in the low-Km forecast than in the high-Km forecast. The deeper and stronger hurricane vortex with lower static stability in the low-Km forecast is more resilient to shear than that in the high-Km forecast.With a smaller vortex tilt in the low-Kli forecast, downdrafts associated with the vortex tilt are reduced, bringing less low-entropy air from the midlevels to the boundary layer, resulting in a less stable boundary layer. Future physics upgrades in operational hurricane models should consider this chain of multiscale interactions to assess their impact on model RI forecasts.

Original languageEnglish (US)
Pages (from-to)853-871
Number of pages19
JournalMonthly Weather Review
Volume147
Issue number3
DOIs
StatePublished - Mar 1 2019

Keywords

  • Boundary layer
  • Numerical analysis/modeling
  • Numerical weather prediction/forecasting
  • Parameterization
  • Subgrid-scale processes
  • Tropical cyclones

ASJC Scopus subject areas

  • Atmospheric Science

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