ORCID

https://orcid.org/0000-0001-5756-901X

Date of Award

Summer 2025

Language

English

Embargo Period

7-17-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Atmospheric and Environmental Sciences

Program

Atmospheric Science

First Advisor

Lance Bosart

Committee Members

Andrea Lopez Lang, Paul Roundy, Ryan Torn, Andrew Winters

Keywords

Synoptic-dynamic meteorology, weather regimes, atmospheric rivers, Madden–Julian Oscillation, eddy-mean flow interactions

Subject Categories

Atmospheric Sciences | Climate | Meteorology

Abstract

Weather regimes are characterized as patterns of low-frequency variability in the middle to upper troposphere of the extratropics. Weather regimes can also be linked to variations in surface weather, making the study of weather regimes a bridge between traditional synoptic-dynamic meteorology and subseasonal-to-seasonal variability. This dissertation identifies and categorizes persistent flow regimes (PFRs), analyzes the dynamics underpinning PFR formation, identifies the linkages to atmospheric teleconnections, and examines the occurrence of surface weather extremes before and during PFRs.

PFRs are identified from 1979–2022 and grouped into five clusters using k-means clustering, which then allows for time-lag composite analysis to determine the dynamical mechanisms underpinning PFR formation. PFRs occur about three times each winter season and tend to last between 10 to 14 days, with a small subset of cases lasting up to 40 days. PFR formation generally occurs in the week before the start of each PFR, with some variation between different clusters. Most PFRs develop from a combination of long-lived Rossby wave trains traveling across the Northern Hemisphere, eddy-mean flow interactions at the eastern end of the oceanic storm tracks, and antecedent blocking highs over high latitudes.

The relationship between PFRs and teleconnections such as the Madden–Julian Oscillation (MJO) and the North Pacific jet phase (NPJ) are established for periods before, during, and after PFR lifecycles. Phases 6 and/or 7 of the MJO are found to be statistically significantly more frequent in the two weeks leading up to the formation of all five PFR clusters. The relationship between PFRs and the NPJ is more varied, but more phases of the NPJ are significantly different from climatology than for the MJO. By compositing select subsets of MJO events preceding PFRs, the pathway for tropical-extratropical interactions can be examined. In many of MJO subsets, the anomalous convection is far away from the Noth Pacific jet, and the orientation and strength of the jet is not as conducive for Rossby wave propagation across the North Pacific.

The frequency of surface weather extremes (extreme cold or warm temperatures and atmospheric rivers (ARs)) are assessed for periods before and during PFRs. Temperature extremes are up to four times more likely to occur during PFRs than climatology both before and during PFRs, especially across western North America, Europe, and the Arctic. AR frequencies range from half to double the expected number of ARs both before and during PFRs, representing shifts of the climatological storm tracks. Composite analysis of ARs that are associated with PFRs versus non-PFR ARs reveals that ARs during PFRs tend to have stronger low-level (850-hPa) wind anomalies rather than stronger moisture anomalies, suggesting a dynamical rather than thermodynamical impact of PFRs on ARs.

License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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