Effects of Surface Flux Parameterization on the Numerically Simulated Intensity and Structure of Typhoon Morakot(2009)

The effects of surface flux parameterizations on tropical cyclone（TC） intensity and structure are investigated using the Advanced Research Weather Research and Forecasting（WRF-ARW） modeling system with high-resolution simulations of Typhoon Morakot（2009）.Numerical experiments are designed to simulate Typhoon Morakot（2009） with different formulations of surface exchange coefficients for enthalpy（C_K） and momentum（C_D） transfers,including those from recent observational studies based on in situ aircraft data collected in Atlantic hurricanes.The results show that the simulated intensity and structure are sensitive to C_K and C_D,but the simulated track is not.Consistent with previous studies,the simulated storm intensity is found to be more sensitive to the ratio of C_K/C_D than to C_K or C_D alone.The pressure-wind relationship is also found to be influenced by the exchange coefficients,consistent with recent numerical studies.This paper emphasizes the importance of C_D and C_K on TC structure simulations.The results suggest that C_D and C_K have a large impact on surface wind and flux distributions,boundary layer heights,the warm core,and precipitation.Compared to available observations,the experiment with observed C_D and C_K generally simulated better intensity and structure than the other experiments,especially over the ocean.The reasons for the structural differences among the experiments with different C_D and C_K setups are discussed in the context of TC dynamics and thermodynamics.

Recent advancements in aircraft and in situ observations of tropical cyclones

Observations of tropical cyclones(TC)from aircraft and in situ platforms provide critical and unique information for analyzing and forecasting TC intensity,structure,track,and their associated hazards.This report,prepared for the tenth International Workshop on Tropical Cyclones(IWTC-10),discusses the data collected around the world in TCs over the past four years since the IWTC-9,improvements to observing techniques,new instruments designed to achieve sustained and targeted atmospheric and oceanic observations,and select research results related to these observations.In the Atlantic and Eastern and Central Pacific basins,changes to operational aircraft reconnaissance are discussed along with several of the research field campaigns that have taken place recently.The changes in the use and impact of these aircraft observations in numerical weather prediction models are also provided along with updates on some of the experimental aircraft instrumentation.Highlights from three field campaigns in the Western Pacific basin are also discussed.Examples of in-situ data collected within recent TCs such as Hurricane Ian(2022),also demonstrate that new,emerging technologies and observation strategies reviewed in this report,definitely have the potential to further improve ocean-atmosphere coupled intensity forecasts.

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.