Date of Award

8-1-2021

Language

English

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Atmospheric and Environmental Sciences

Content Description

1 online resource (vi, 84 pages) : color illustrations, color maps.

Dissertation/Thesis Chair

Robert RF Fovell

Keywords

Numerical Weather Prediction, Tropical Cyclone, Cyclones, Boundary layer (Meteorology), Surface roughness, Coasts, Hurricanes, Marine meteorology

Subject Categories

Atmospheric Sciences

Abstract

Hurricane Karl (2010) underwent unexpected rapid intensification in the Bay of Campeche while remaining in close proximity (within 150 km) to land. It is hypothesized that the frictionally-enhanced inflow contributed positively to this evolution, despite reduced surface fluxes and increased momentum loss over land. In this study, the role of differential friction in the development of a tropical cyclone (TC) tracking parallel to a coastline is examined based on this prototype.A series of high-resolution, semi-idealized numerical simulations with full physics were conducted on a β-plane with curvature effects of the Earth. After initializing a TC from a synoptic-scale thermal perturbation, a crescent-shaped piece of land with uniform land use category and no elevation was introduced at an arbitrary distance from the TC center (about 150 km initially). The TC drifted towards the north due to the β effect, while interacting with the land during the next three days. Two experiments with surface roughness length (Z0) over land set to 50.0 cm and 0.01 cm, respectively, were selected to analyze the simulated TC’s evolution with the presence and absence of distant friction. It was found that the simulation with higher friction over land produced a TC that was slightly more intense, about 5 hPa deeper and 5 m s-1 stronger, by hour 48 into the simulation. An area of mechanically-forced convergence was present along the coast in the lower planetary boundary layer (PBL). This TC commenced faster intensification a few hours earlier than its lower-friction counterpart, following a period of vertical wind shear reduction and upshear moistening. Calculations of the gradient wind balance residual in the lower PBL revealed an enhanced wavenumber-two asymmetry, with radially-inward acceleration located downwind of the coastal convergence zone, as well as on the mirroring side with respect to the TC center, and an overall smaller radius of maximum wind. A quasi-stationary coastal rainband was present at times, co-located with the coastal convergence zone, the evaporative cold pools from which reinforced the PBL imbalance and buoyancy gradient just outside the TC inner core. A similar rainband structure was also observed in Hurricane Karl (2010) during its rapid intensification, but persisted for a longer period of time. A small ensemble of simulations with varying distance between the TC and the land produced similar results (up to 10 hPa deeper with land at an “ideal” distance). Findings from this study suggest the importance of properly representing land characteristics in numerical models even when forecasting TCs with no immediate landfall.

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