Effects of Appalachian Topography on Precipitation from Landfalling Hurricanes

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Title: Effects of Appalachian Topography on Precipitation from Landfalling Hurricanes
Author: Harville, Steven L.
Advisors: Sandra Yuter, Committee Member
Gary Lackmann, Committee Member
Anantha Aiyyer, Committee Chair
Abstract: A thorough analysis of rainfall distributions associated with tropical cyclones that have impinged upon or impacted the southern and central Appalachian mountain range is conducted using the North America Regional Reanalysis (NARR) and the Weather Research and Forecasting (WRF) model. The primary objective of this study is to improve the skill and precision of future forecasts by identifying specific areas where enhancement of the precipitation associated with landfalling tropical cyclones due to the direct and indirect effects of orography most frequently occurs. Based on the relative positions between the tropical cyclone tracks and the orientation of the Appalachian Mountains, four storm tracks are classified. We identify locations with the highest potential for flooding using local maximum analysis for each representative track. For storms that run parallel along the eastern side of the Appalachians (Track-B), heavy rainfall is located along eastern slopes with the heaviest precipitation falling across western North Carolina and central Virginia. Storm tracks that run parallel on the western side of the Appalachians (Track-C) show heaviest precipitation falling on the eastern slopes of western North Carolina. For storms that track more perpendicular to the mountain range, maximum rainfall is located over the mountains of central Virginia (Track-A) and across the southern Appalachians (Track-D). A second goal of this work is to document some of the effects of these mountains on landfalling tropical cyclones, on the synoptic environment as a whole, and on the interactions of these tropical and mid-latitude cyclones. Work here is focused on expanding upon the synoptic approach of Atallah et al. (2007). This is accomplished through examination of the precipitation climatology, analysis of composites and case studies, and by numerical simulation. Hart and Evans (2006) find that the orientation of the approaching upper-level mid-latitude trough is one of the most significant factors in determining the occurrence of extratropical transition (ET) and the potential for reintensification. Results suggest that through orographic enhancement of the downstream ridge, these storms play an active role in tilting the approaching mid-latitude trough towards a more negative orientation, thus increasing the likelihood of ET. At the same time synoptic-scale frontal boundaries slow and strengthen as they approach the Appalachians from the west, similar to the findings of O'Handley and Bosart (1996). As a result, numerical simulations run with topography show greater precipitation over areas northwest of the Appalachians than experimental simulations run with flattened terrain.
Date: 2009-04-13
Degree: MS
Discipline: Marine, Earth and Atmospheric Sciences
URI: http://www.lib.ncsu.edu/resolver/1840.16/2849

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