SENSITIVITY OF HURRICANE INTENSITY AND STRUCTURE TO TWO TYPES OF PLANETARY BOUNDARY LAYER PARAMETERIZATION SCHEMES IN IDEALIZED HWRF SIMULATIONS

This paper investigates the sensitivity of simulated hurricane intensity and structure to two planetary boundary layer(PBL) schemes in the Hurricane Weather and Research Forecast model including 1) the GFS scheme(control run) that uses the K-profile method to parameterize turbulent fluxes, and 2) the MYJ scheme that is based on turbulent kinetic energy(TKE) budget for turbulent closure. Idealized simulations with these two PBL schemes show that the storm in the TKE run is stronger than that in the control run after three days into simulation. Multi-scale structures are evaluated and compared between the control and the TKE runs prior to the divergence of the model-simulated intensity to elucidate the mechanism underlying such a difference in the intensity between the two runs. It is found that the storm in the TKE run has i) a shallower boundary layer with a stronger PBL inflow, ii) stronger boundary layer convergence closer to the storm center, iii) higher vorticity and inertial stability inside the RMW; iv) stronger and deeper updrafts in regions further inward from the radius of maximum wind(RMW), and v) more convective bursts located near the RMW as compared to the control run. Angular momentum budget analysis suggests that the convergence of angular momentum in the boundary layer is much stronger in the TKE run than in the control run, which is responsible for faster spin-up of the hurricane vortex in the TKE run.

A DEVELOPMENTAL FRAMEWORK FOR IMPROVING HURRICANE MODEL PHYSICAL PARAMETERIZATIONS USING AIRCRAFT OBSERVATIONS

As part of NOAA’s Hurricane Forecast Improvement Program(HFIP),this paper addresses the important role of aircraft observations in hurricane model physics validation and improvement.A model developmental framework for improving the physical parameterizations using quality-controlled and post-processed aircraft observations is presented,with steps that include model diagnostics,physics development,physics implementation and further evaluation.Model deficiencies are first identified through model diagnostics by comparing the simulated axisymmetric multi-scale structures to observational composites.New physical parameterizations are developed in parallel based on in-situ observational data from specially designed hurricane field programs.The new physics package is then implemented in the model,which is followed by further evaluation.The developmental framework presented here is found to be successful in improving the surface layer and boundary layer parameterization schemes in the operational Hurricane Weather Research and Forecast(HWRF) model.Observations for improving physics packages other than boundary layer scheme are also discussed.