Sensitivity of Numerical Simulations of the Rapid Intensification of Hurricane Katrina (2005) to Boundary Layer Parameterization Schemes

A rapid intensification process of Hurricane Katrina (2005) before its landfall in the southern US is studied. Numerical simulations are conducted with an advanced research version of the Weather Research and Forecasting (WRF) model. Sensitivity of numerical simulations to two popular planetary boundary layer (PBL) schemes, the Mellor-Yamada-Janjic (MYJ) and the Yonsei University (YSU) schemes, is investigated. Large discrepancies (e.g., over 10 hPa in simulated minimum sea level pressure) are found in the two simulations during the rapid intensification period. Further diagnoses of results indicate that stronger surface fluxes and vertical mixing in the PBL from the simulation with the MYJ scheme lead to enhanced air-sea interactions, which helps generate more realistic simulations of rapid intensification processes. Overall results from this study suggest that improved representation of surface fluxes and vertical mixing in the PBL is essential for accurate prediction of hurricane intensity changes.