Tropical cyclone (TC) size is integral in determining the spatial extent of TC impacts and is influenced by environmental wind shear and the overall moisture environment. Since initial TC size is related to future TC size, research focused on understanding the influences of TC size away from land can lead to a more complete understanding of the extent of coastal impacts associated with landfalling TCs. This study considers TCs located in an area of low to moderate wind shear located at least 100 km from major land masses. An empirical orthogonal function (EOF) analysis is used to distinguish different environments based on the large-scale spatial pattern of total column water vapor (TCWV) surrounding the TC. Using these EOF patterns, four separate categories (groups) are created. Principal component (PC) scores indicate the time steps most contributing to the EOF pattern for each group and ultimately determine the time steps included in each group. TC sizes among the groups are compared using size metrics based on the wind field and shape metrics based on the precipitation field. These metrics are considered at the central timestep identified in the EOF analysis as well as a 48-hour window centered on the central timestep. There are no significant differences in the wind field size, but TCs with moisture to the southeast are the largest in terms of overall precipitation area. This suggests that moisture affects the size of the precipitation field but not the wind field. However, more research is needed to confirm this relationship. Storms with moisture to the southeast are also more intense and younger than TCs in other groups and show signs of inner core organization and subsequent intensification while TCs in the other groups do not. TCs in an extremely dry environment or with dry air to the southeast of the TC center are generally smaller, less closed, less solid, and older than TCs with moisture to the southeast and TCs with dry air to the northwest of the TC center. An additional analysis comparing the same size and shape metrics between TCs experiencing easterly and westerly shear is also completed. The wind shear results suggest that, while easterly shear is more commonly associated with younger and intensifying TCs regardless of moisture group, an environment with westerly shear is more favorable for intensification of TCs with moisture to the southeast due to the alignment of moisture and upward motion. Future work will investigate the physical processes contributing to these precipitation shape and size differences between groups and wind shear directions. / Master of Science / The size of tropical cyclones (TCs) is heavily influenced by moisture and wind shear. Wind shear is defined as the changing of wind direction with vertical height in the atmosphere. Research focused on investigating how moisture and wind patterns affect the size and structure of TCs can lead to a better understanding of the physical extent of impacts associated with landfalling TCs and advise more effective emergency preparedness plans. This research considers TC time steps located over the ocean and in a calm wind environment. From here, time steps are divided into four groups representing common moisture patterns in the Atlantic basin. TC size is evaluated using size and shape metrics designed to capture the spatial extent and layout of wind and rain associated with the storm. This research also compares the evolution of these size and shape metrics to better understand how the environment around the TC changes over time. Results show that the extent of wind associated with the storm is similar across all groups but TCs with moisture to the southeast are the largest in terms of overall rain area. This suggests that moisture affects the extent of precipitation but not the extent of wind or that wind data are inaccurate. Additionally, TCs with moisture to the southeast are younger and stronger than storms in the other groups. TCs in extremely dry environments and TCs with dry air to the southeast are generally smaller, weaker, and older than TCs in the other groups. In looking at the evolution of these size and shape metrics, TCs with moisture to the southeast group become stronger with time while TCs in the other groups do not. An additional analysis comparing TCs experiencing different wind patterns is completed. Results of this show that, while easterly wind shear, characterized by surface winds out of the west and upper level winds out of the east, is more commonly associated with strengthening TCs when moisture is not considered, TCs with moisture to the southeast in an environment with westerly wind shear are more likely to strengthen over time due to the alignment of moisture with favorable environmental conditions within the storm by the overall wind pattern. Westerly shear is characterized by winds at the surface out of the east and upper level winds out of the west. Future work should focus on the environmental processes contributing to the size and shape differences observed between moisture groups and wind patterns.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115368 |
| Date | 07 June 2023 |
| Creators | Addington, Kayleigh Dae |
| Contributors | Geography, Zick, Stephanie E., Ellis, Andrew, Bukvic, Anamaria |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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