Date of Award

5-11-2016

Document Type

Restricted Access Thesis

Degree Name

Master of Science in Applied Meteorology

Department

Department of Atmospheric Sciences and Chemistry

Thesis Advisor

Eric G. Hoffman

Committee Member

Jason M. Cordeira

Committee Member

Heather M. Archambault

Abstract

Recent literature demonstrates that recurving tropical cyclones (TCs) induce a response in the downstream midlatitude flow. Related research explores the differences in the response of the downstream flow to recurving TCs and extratropical cyclone events. This thesis expands upon the existing research by exploring the downstream response to explosive cyclone intensification over the North Pacific. Using a sample of 295 cases of explosive cyclone intensification within the domain (30°N–70°N, 140°E–220°E) during a nine-year period from 2006–2014, cyclone-relative composite analyses of the downstream midlatitude flow are analyzed. Explosively deepening cyclones are stratified by criteria based on both deepening rate and minimum pressure, location within the domain, i.e., West and East Pacific, and season. Time-lagged composite analyses of standardized meridional wind and geopotential height anomalies reveal amplitude differences in the downstream response based on cyclone deepening rate and minimum pressure for each respective location. Strong cyclones, those that deepen faster to a lower minimum pressure, are associated with greater magnitude anomalies. Differences in the downstream response to cyclones over the West and East Pacific are observed. Downstream Rossby wave propagation following West Pacific cyclones was generally more progressive, and primarily acted to amplify a quasi-stationary ridge in the Central Pacific and weaken the climatological ridge over the North American west coast, whereas explosively deepening cyclones in the East Pacific amplified the West Coast ridge. The signal of a coherent, statistically significant composite downstream response diminishes 72 h following explosive intensification for both locations and all strengths. The season and location of explosive cyclone occurrence play significant roles in determining the persistence, amplitude, and spatial distribution of the downstream flow response. West Pacific cyclones during the spring and autumn seasons are associated with downstream responses of similar position, with more persistent statistically significant anomalies present following spring cyclones. East Pacific spring cyclones induce a greater amplitude, shorter wavelength, and more persistent downstream response than corresponding autumn events. A weaker meridional gradient of the downstream upper-tropospheric potential vorticity waveguide downstream of the composite cyclone likely inhibits the downstream response after 72 h. Composite analysis of the dynamic evolution of the downstream response, initiated by the negative upper-tropospheric potential vorticity advection by the irrotational wind, suggest weak diabatic contributions to explosive intensification compared to studies of recurving TCs. This overall weaker diabatic contribution to amplification of the large-scale flow likely results in a shorter-lived downstream response. Composite analyses additionally suggest that antecedent downstream flow structure may impact the persistence and position of downstream features following explosive cyclone intensification. Cyclone-relative composite analyses suggest that explosively deepening Pacific cyclones may be associated with downstream sensible weather events. Explosively deepening East Pacific cyclones during the spring appear to create conditions favorable for thunderstorm development in the southern United States, whereas West Pacific events during the same season appear to be associated with anomalous warming in the central U.S. Winter East Pacific cyclones additionally appear to be associated with conditions favorable for heavy precipitation events along the U.S. west coast and winter precipitation events in the Northeast, as well as anomalous warming events in northern and central Canada.

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