Date of Award

12-1-2022

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 (x, 109 pages) : illustrations (some color), maps (some color)

Dissertation/Thesis Chair

Lance F Bosart

Committee Members

Kristen Corbosiero

Keywords

Precipitation (Meteorology), Climatic extremes, Severe storms, Atmospheric circulation

Subject Categories

Atmospheric Sciences

Abstract

Extreme precipitation events (EPEs), characterized by daily widespread heavy rainfall exceeding the 95th percentile across Central America, can have large impacts on agriculture, life, and property during the rainy season. EPEs during the Northern Hemisphere (NH) autumn, however, have been observed to be influenced by both tropical and extratropical originating phenomena such as easterly waves and cold surges, respectively. Given the limited research in this area, the novelty of this work is to apply a systematic approach for identifying and better understanding EPEs, and investigating their associated synoptic-scale variability using daily high-resolution observations and reanalysis products over Central America. An examination of Central American EPEs during the autumn, defined by exceeding the 95th percentile of daily precipitation, was performed using the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSSIAN-CDR). Additionally, a climatology of the associated large-scale flow features related to the formation and evolution of EPEs from 1983–2018 was objectively categorized and extracted using self-organizing maps (SOMs) using the NCEP Climate Forecast System Reanalysis (CFSR) reanalysis. A time-lagged composite analysis of thermodynamic and dynamic variables (e.g., K-index, integrated vapor transport, and moisture flux convergence) using SOMs was then performed on binned EPEs to document the evolution of the dominant fields that generally lead to EPEs identified in the constructed climatology. Diagnostic fields used to investigate the evolution of EPEs were applied to two representative case studies included in this thesis for consistency and comparison purposes. The monthly frequency of daily EPEs over Central America during autumn is generally confined to enhanced terrain where upslope flow is highly favored. Based on the observed local synoptic features throughout autumn, EPEs are commonly associated with two dominant scenarios characterized by the presence of Central American gyres (CAGs) or cold surges prior to an EPE onset. CAG patterns favor EPE precipitation along the Pacific coastline of Central America as opposed to cold surges that favor heavy precipitation along the Caribbean coastline of Central America. Finally, the representative case studies further demonstrate the evolution and processes associated with CAG and cold surge patterns as depicted by SOMs. The first representative case study that was associated with a CAG featured the interactions of a potential vorticity streamer (PVS), a Southern Hemisphere (SH) dry air surge, and two tropical cyclonic circulations that precluded widespread heavy rainfall primarily the Pacific-facing slopes of Central America. The second representative case study highlighted the importance of NH extratropical influences that manifested in the form of a cold air surge within a convectively favorable environment that supported widespread heavy rainfall across Central America.

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