Date of Award
2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Oceanography
Specialization
Marine Geology and Geophysics
Department
Oceanography
First Advisor
Isaac Ginis
Abstract
The impact of land surface roughness on the hurricane boundary layer (HBL) wind structure is crucial for understanding and predicting wind damage during landfall. Accurate representation of these surface conditions is essential for realistic wind simulations. This Ph.D. dissertation investigates the impact of land surface roughness on hurricane wind prediction during landfall. By simulating the flow within the HBL using a 3D boundary layer wind model, we evaluate the model's ability to predict wind speeds over land surfaces. A new approach for hurricane vortex generation was developed for the HBL model to ensure a realistic representation of the hurricane wind structure, and the 2019 National Land Cover Database was incorporated to accurately represent land surface characteristics. This research underscores the importance of accurately representing land surface roughness in predicting hurricane winds during landfall. Our results demonstrate that a boundary layer model with realistic land surface representation can skillfully simulate land-based wind speeds.
Chapter 1 introduces the Hurricane Boundary Layer (HBL) model and a new vortex generation method that utilizes the National Hurricane Center's “Best Track” dataset. Our approach aims to generate a realistic 3D wind structure within the hurricane boundary layer consistent with observations. To evaluate the model’s performance, we conducted simulations of Hurricanes Irma (2017), Florence (2018), and Michael (2018). Comparisons with NHC intensity and wind structure estimates, along with validation against airborne Stepped Frequency Microwave Radiometer data and fixed-point surface wind measurements over water, demonstrated the model's ability to skillfully simulate surface winds.
Chapter 2 investigates the impact of land surface roughness on the hurricane’s surface wind structure through idealized simulations using the HBL model. Model results revealed that an initially axisymmetric hurricane vortex becomes asymmetric well before the center reaches land. As the hurricane moves toward the coast, both the radial and the tangential winds increase in areas where the wind is directed offshore. This leads to a shift in the hurricane’s maximum wind speed to the left of the track. Analysis of the hurricane’s momentum budget revealed that the initiation of the changes in the hurricane’s wind structure was first triggered by a reduction in tangential wind speed over land due to land-induced friction, which is then advected offshore by the hurricane's primary circulation. Enhancement of the angular momentum advection by the increased radial acceleration along with the azimuthal advection of the tangential wind contributes to the increase of tangential wind in the rear-left quadrant. Radial and azimuthal advection of the radial wind also play significant roles in developing wind asymmetry. Sensitivity experiments further reveal that the temporal evolution of the surface wind changes during landfall depends on the translation speed, hurricane size, and land surface roughness length.
Chapter 3 evaluates the performance of the HBL model in simulating surface winds during landfalls of Hurricanes Irma (2017), Florence (2018), and Michael (2018). High-resolution land cover datasets were incorporated to represent land surface roughness accurately. The models' performance was assessed by comparing the time series of the simulated wind speed and wind direction over land from land-based anemometers. Additionally, we evaluated the skill of the model in simulating the observed peak wind speed over land by comparing it with the observed peak wind speed. The Root Mean Square Error (RMSE) ranged between 2.42 to 3.03 m/s-1, demonstrating the model's ability to simulate surface winds over land skillfully.
Recommended Citation
Jisan, Mansur Ali, "DEVELOPMENT AND APPLICATION OF A HURRICANE BOUNDARY LAYER WIND MODEL FOR LANDFALLING HURRICANES" (2024). Open Access Dissertations. Paper 1640.
https://digitalcommons.uri.edu/oa_diss/1640