Impacts of planetary boundary layer parameterization in RegCM4.7 on the intensity and structure of simulated tropical cyclones over the Philippines

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The influence of planetary boundary layer (PBL) parameterization on tropical cyclones (TCs) over the Philippine region is examined using the Holtslag and the University of Washington (UW) schemes in RegCM4.7 at 25-km resolution. Comparisons made between the model-simulated TCs and best track data indicate that more TCs were reproduced in both the RegCM4.7 simulations than the ERA-Interim reanalysis. It is further revealed that while only small biases were obtained in the number of TCs detected from the two RegCM4.7 simulations, only the UW scheme was able to simulate strong (Category 4–Category 5) TCs. A composite analysis on the radial cross section of azimuthally averaged wind fields shows that the UW scheme generates stronger wind velocities with narrower and elevated maximum tangential wind, and enhances low-level momentum convergence, compared with the Holtslag scheme. In addition, the radial positioning of the strong diabatic heating of UW simulation within the radius of maximum wind supported the needed conditions for warmer core formation and contributed to the enhancement of the secondary circulation by vertical advection of high absolute angular momentum, hence the higher intensity of TCs. The resulting higher surface maximum winds with increased diabatic heating within the eyewall and stronger warm-core structures in the UW simulation suggest that the induced convergence has offset the dissipative effects of momentum loss more than that in the Holtslag run.