Improving Numerical Weather Forecasts of Tropical Cyclones Through a Better Understanding of Surface and Boundary Layer Processes

Open Access
- Author:
- Green, Benjamin Weiss
- Graduate Program:
- Meteorology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 05, 2015
- Committee Members:
- Fuqing Zhang, Dissertation Advisor/Co-Advisor
Fuqing Zhang, Committee Chair/Co-Chair
Raymond Gabriel Najjar Jr., Committee Member
Marcelo Chamecki, Committee Member
Jinchao Xu, Special Member
Christopher Davis, Special Member - Keywords:
- Tropical cyclones
hurricanes
air-sea interaction
numerical weather prediction
weather forecasting - Abstract:
- Tropical cyclones (TCs) can pose substantial threats to life, property, and infrastructure. In order to minimize these losses, accurate forecasts of both TC track and intensity are needed with a sufficient amount of lead-time. Although track forecasts have consistently improved over the past 25 years, intensity forecasts have not because key small-scale processes – including fluxes of momentum and moist enthalpy across the air-sea interface as well as boundary layer mixing – must be represented in the most advanced numerical weather prediction (NWP) models by inherently incorrect parameterizations. Therefore, it is believed that improved parameterization of surface fluxes and boundary layer turbulence in NWP will lead to improved forecasts of TC intensity – the overarching theme of this dissertation. Chapter 1 provides a broad introduction to the dissertation. In Chapter 2, Weather Research and Forecasting (WRF) simulations are conducted to elucidate the impact of surface flux parameterization on TC intensity and structure; it is found that TC intensity, as well as the relationship between the TC’s minimum sea level pressure and maximum 10-m wind speed, is highly sensitive to flux parameterization. These findings are expanded upon in Chapter 3, which details a more systematic investigation of the flux parameterizations and shows that the drag coefficient changes the pressure-wind relationship and the TC radius of maximum winds. In Chapter 4, idealized large-eddy simulations of a TC-like boundary layer produce turbulent rolls comparable in size to observations. Chapter 5 investigates WRF simulations of TCs in the turbulent gray zone (where large turbulent eddies are only partially resolved) and concludes that the choice of subgrid-scale parameterization is crucial, but higher resolution is needed to study TC boundary-layer turbulence. Chapter 6 shows that data assimilation can be used to estimate model parameters related to the surface exchange coefficients. Chapter 7 summarizes the results of the dissertation.