Characteristics and mechanisms of cold air outbreaks in the central and eastern United States

Solecki, Zachary

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https://hdl.handle.net/2142/129991 Copy

Description

Title

Characteristics and mechanisms of cold air outbreaks in the central and eastern United States

Author(s)

Solecki, Zachary

Issue Date

2025-07-25

Director of Research (if dissertation) or Advisor (if thesis)

• Wang, Zhuo
• Rauber, Robert M

Committee Member(s)

Walsh, John E

Department of Study

Climate Meteorology & Atm Sci

Discipline

Atmospheric Sciences

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

Cold air outbreaks

Abstract

Cold air outbreaks (CAOs) can have significant impacts on the ecosystem, infrastructure, and public health, particularly in North America. This study develops a gridpoint-based definition of CAOs and investigates the climatology, characteristics, and evolution in CAOs in the central and eastern continental U.S. Our analysis shows a notable peak in both CAO events and CAO days in the late 1970s followed by a decline in the 1980s and subsequent leveling off in recent decades. Additionally, the mean CAO duration decreases from 8.93 days pre-1980 to 6.35 days post-1980. CAO occurrence increases in the negative phase of AO or NAO, while the link between CAOs and the PNA or ENSO is weak. A K-means clustering algorithm identifies five types of CAOs of different location, size, intensity, propagation speed, and duration. In particular, Clusters 1 and 3 impact southeastern US; Cluster 2 and 4 effect central U.S., and Cluster 5 is the most extensive and persistent type, impacting most of the central and eastern U.S. While all CAOs are characterized by an anomalous cyclone over the central or eastern US, Clusters 1 and 3 are characterized by a dipole pattern over the North Atlantic, which projects to the negative phase of the NAO and AO, while Clusters 2, 4, and 5 exhibit a wavetrain pattern over the North Pacific and North America. The specific location and intensity of the circulation patterns differ between clusters, contributing to their unique characteristics. Additionally, our results highlight different troposphere-stratosphere interactions for different CAO clusters. The LAGRANTO 2.0 analysis tool is used to trace 7-day parcel back-trajectories from the center of the defined CAOs as a means of investigating the source of these airmasses as well as their evolution. It is found that air parcels within CAOs generally originate in the Arctic, and experience a nearly constant rate of radiative cooling along their path. These air parcels spend spend most of this 7-day period north of 50°N, and are generally located above the surface before rapid subsidence in the final day of their trajectory. This is in contrast to non-CAO parcels, which comparatively spend more time near the surface and/or in mid- and subtropical-latitudes. It is also found that CAO temperature anomalies show a strong relationship with parcel source potential temperature, but little relationship with parcel source potential temperature anomalies. This suggests that a key factor in the intensity of CAOs is the anomalous movement of Arctic airmasses into the mid-latitudes, rather than anomolous thermodynamic states in the Arctic.

Graduation Semester

2025-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129991

Copyright and License Information

Copyright 2025 Zachary Solecki

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