Impact of parameterized boundary layer structure on tropical cyclone rapid intensification forecasts in HWRF

Jun A. Zhang, Robert F. Rogers, Vijay Tallapragada

Research output: Contribution to journalArticlepeer-review

43 Scopus citations

Abstract

This study evaluates the impact of the modification of the vertical eddy diffusivity (Km) in the boundary layer parameterization of the Hurricane Weather Research and Forecasting (HWRF) Model on forecasts of tropical cyclone (TC) rapid intensification (RI). Composites of HWRF forecasts of Hurricanes Earl (2010) and Karl (2010) were compared for two versions of the planetary boundary layer (PBL) scheme in HWRF. The results show that using a smaller value of Km, in better agreement with observations, improves RI forecasts. The composite-mean, inner-core structures for the two sets of runs at the time of RI onset are compared with observational, theoretical, and modeling studies of RI to determine why the runs with reduced Km are more likely to undergo RI. It is found that the forecasts with reduced Km at the RI onset have a shallower boundary layer with stronger inflow, more unstable near-surface air outside the eyewall, stronger and deeper updrafts in regions farther inward from the radius of maximum wind (RMW), and stronger boundary layer convergence closer to the storm center, although the mean storm intensity (as measured by the 10-m winds) is similar for the two groups. Finally, it is found that the departure of the maximum tangential wind from the gradient wind at the eyewall, and the inward advection of angular momentum outside the eyewall, is much larger in the forecasts with reduced Km. This study emphasizes the important role of the boundary layer structure and dynamics in TC intensity change, supporting recent studies emphasizing boundary layer spinup mechanism, and recommends further improvement to the HWRF PBL physics.

Original languageEnglish (US)
Pages (from-to)1413-1426
Number of pages14
JournalMonthly Weather Review
Volume145
Issue number4
DOIs
StatePublished - Apr 1 2017

Keywords

  • Boundary layer
  • Model evaluation/performance
  • Numerical weather prediction/forecasting
  • Operational forecasting
  • Subgrid-scale processes
  • Tropical cyclones

ASJC Scopus subject areas

  • Atmospheric Science

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