Date of Award




Document Type

Master's Thesis

Degree Name

Master of Science (MS)


Department of Atmospheric and Environmental Sciences

Content Description

1 online resource (viii, 119 pages) : illustrations (some color), color maps.

Dissertation/Thesis Chair

Lance F Bosart

Committee Members

Andrea A Lopez Lang


Atmospheric blocking, Atmospheric rivers, Dynamic Meteorology, Subseasonal to seasonal variability, Synoptic Meteorology, Atmospheric circulation, Water vapor transport, Upper atmosphere, Synoptic meteorology, Drought forecasting

Subject Categories

Atmospheric Sciences


Along the west coast of North America (NA), a majority of the precipitation for the entire year falls during winter as a result of approximately a dozen cyclones or atmospheric rivers. However, persistent upper-level ridges can prevent the occurrence of wintertime precipitation events and lead to extended drought, significant water shortages, and adverse economy-wide impacts for major population centers in California. An increased understanding of the dynamical and thermodynamical processes that govern upper-level ridge formation, persistence, and dissipation during the rainy season along western NA would allow decision makers to better manage water resources and motivates this thesis. Persistent upper-level ridges will be defined by positive 500-hPa height anomalies ≥1.0 standard deviation that last for longer than 7 days, constructed using NCEP-NCAR reanalysis from 1948–2017. This resulting climatology will be used to construct composite analyses based off four pre-defined domains to uncover dynamical and thermodynamical linkages between persistent ridge regimes in different domains. Statistical relationships with teleconnections and case study examination are included in this presentation to further explain the evolution of persistent ridges. Composite analysis of the persistent ridge lifecycle shows different dynamical processes are important for persistent ridges in each domain, but nearly all composites highlight important interactions with upstream cyclones throughout the ridge lifecycle. In the statistical relationships, it was found that the phase of the North Pacific jet stream had the most statistically-significant frequency anomalies up to 10 days prior to the start of a persistent ridge, while the Arctic Oscillation had a much weaker relationship for most of the persistent ridges. Finally, the case study further demonstrates some of the dynamical and thermodynamical processes found through the composite analysis, with the biggest emphasis on repeated cyclogenesis aiding in the maintenance of a quasi-stationary ridge.