A TALE OF TWO FORCES. How Thermodynamic and Dynamic Forces Contributed to the Record-Breaking Rainfall in the 2018 Kauai Rainfall Event.
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2024
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Abstract
The interactions of deep moist convection, particularly supercell storms, in the vicinity of substantial terrain, is a relatively under-investigated research topic, especially for sub-tropical coastal locations. While terrain-influenced supercell storms are rare in the subtropics, when they do occur, they often result in prolific rainfall and other weather-related hazards. The islands of Hawaii and their complex terrain features have each hosted many terrain-influenced storms and subsequently produced weather-related hazards ranging from bow echoes, hail, flash-flooding, and tornadoes. Perhaps the most notable case, the 14-15th of April 2018, Kauai rainfall event consisted of a series of three distinct rainfall periods, each supporting radar-inferred evidence of meso-cyclonic rotation, and together breaking the U.S. 24-h rainfall record, with 1262 mm (just under 50 inches) of rainfall reported at Waip ̄a Garden. To this end, Chapter 1 introduces heavy rainfall events, their properties, and their occurrences in Hawai‘i. Chapter 2 thoroughly investigates the observational details of the 2018 Kaua‘i storm event to uncover how a storm of this magnitude evolved, persisted, and produced historic rainfall totals. To substantiate our observational analysis, Chapter 3 investigates this event further with a high-resolution WRF simulation and focuses on the heaviest rainfall period, occurring overnight between 0700-1300 UTC, 15 April 2018. Analyses will focus on properties and features within the upwind storm environment and connect the evolution of convection, vorticity, and cold pools with the trends in rainfall magnitude and location. Lastly, Chapter 4 uses results from Chapter 3 to decompose the total pressure field into its constituent parts related to dynamic and thermodynamic processes using discrete Fourier transformations. With this data, a component analysis of the vertical momentum equation is completed to identify and quantify the mechanisms most responsible for the highly localized, persistent, and historic rainfall during the 2018 Kaua‘i event. Lastly, a summary of the conclusions and discussions is presented in Chapter 5.
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Atmospheric sciences, Meteorology, Cold Pools, Flood Events, Invert Poisson Equation, Numerical Weather Modeling, Orographic Effects, Supercells
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189 pages
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