This study addresses the susceptibility of atmospheric rivers (ARs) to the behavior of the North Atlantic Subtropical High (NASH). ARs are a major mechanism for meridional moisture transport often connected to heavy precipitation and mid-latitude troughs. The NASH, a semi-permanent anticyclone over the subtropical North Atlantic Ocean, has been shown to be significantly influential on precipitation variability over the southeastern United States. A self-organizing map (SOM) was trained on a 4 x 3 regular grid over 250 iterations using ERA5 derived 6-hourly 850 hPa Geopotential Heights ≥ 1535 gpm from 1979-2020. The 12 resulting "nodes" were analyzed with respect to ARs defined by objects of ERA5 derived integrated water vapor transport (IVT) > 500 m-1 s-1 with lengths > 2000 km. Composites of thresholded 850 hPa heights, AR-concurrent PRISM precipitation, AR spatial frequency distribution maps, and seasonal AR frequency histograms per node illustrate seasonal interactions between the NASH and ARs that demonstrate a tendency of more frequent ARs and higher mean AR-driven precipitation over the Mississippi embayment and Ohio River Valley in the summer months, believed to be representative of extreme moisture transport events, when the NASH exhibits increased intensity, spatial expansion, and southwestward migration. Conversely, AR frequency and AR-concurrent precipitation composites suggest wintertime events are mainly supported by dynamically-driven nor'easter and bomb type cyclones when the NASH is constricted, at higher latitudes, and further east. Findings suggest that extreme summertime water vapor transport events associated with an AR are enhanced by the warm season NASH due to its increased intensity and proximity to the eastern US that acts as a supplementary lifting mechanism amidst low dynamic influence. / Master of Science / This study aims to investigate the response of atmospheric rivers (ARs) to the behavior of the North Atlantic Subtropical High (NASH). ARs are a major vehicle for the poleward transport of moisture from the tropics and subtropics. ARs are often affiliated with heavy precipitation and mid-latitude cyclones and frontal boundaries. The NASH, a semi-permanent anticyclone over the subtropical North Atlantic Ocean, has been shown to be significantly influential on precipitation variability over the southeastern United States. A self-organizing map (SOM), a method of vector quantification, was trained on a 4 x 3 regular grid over 250 iterations using ERA5 derived 6-hourly 850 hPa Geopotential Heights ≥ 1535 meters from 1979-2020. The 12 resulting "nodes" were analyzed with respect to ARs defined by objects that result from masking the rate of transport of water vapor within a vertical column from 1000 hPa to 300 hPa of which that are greater than 2000 km long. Composites of thresholded 850 hPa heights, AR-concurrent precipitation, AR spatial frequency distribution maps, and seasonal AR frequency histograms per node illustrate seasonal interactions between the NASH and ARs that demonstrate a tendency of more frequent ARs and higher mean AR-driven precipitation over the Mississippi embayment and Ohio River Valley in the summer months, believed to be representative of severe precipitation events, when the NASH is stronger, larger, and further southwestward. Conversely, AR frequency and AR-concurrent precipitation composites suggest wintertime events are mainly supported by nor'easter and bomb type cyclones that occur when the Polar jet stream is strongest and when the NASH is constricted, at higher latitudes, and further east. Findings suggest that extreme summertime water vapor transport events associated with an AR are enhanced by the warm season NASH due to its increased intensity and proximity to the eastern US that acts as a supplementary lifting mechanism amidst low dynamic influence.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/120682 |
| Date | 22 July 2024 |
| Creators | Finkhauser, Julia Elizabeth Rose |
| Contributors | Geography, Ramseyer, Craig A., Cordeira, Jason, Zick, Stephanie E. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | Creative Commons Attribution-NonCommercial 4.0 International, http://creativecommons.org/licenses/by-nc/4.0/ |
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