Identifying Synoptic Controls on Boundary Layer Thermodynamic and Cloud Properties Using a Regional Forecast Model

Although most of our understanding of boundary-layer cloudiness is based on idealized, subtropical, barotropic marine environments, boundary-layer clouds exist across a range of conditions. In this study, we use the Naval Research Laboratory’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) and an automated cold-front-relative analysis framework to explore the boundary-layer structure associated with low clouds across the cold front of midlatitude synoptic cyclones in the Eastern North Atlantic (ENA). Simulation output is compared against observation from satellite and retrievals from ground-based observations at Graciosa Island in the Azores. Composite transects across the cold front reveal a shallow, conditionally unstable boundary layer in the warm sector, accompanied by overly shallow clouds with low liquid water content, relative to observations. The cold frontal region exhibits convection associated with weak stability and ascent. Northwest of the cold front, the boundary layer is well-mixed, deeper, and capped by a strong inversion maintained by large-scale subsidence. The deep, well-mixed post-frontal boundary layers and cloudiness are maintained by strong surface fluxes, as in cold air outbreaks. Clouds that form in the post-cold-frontal tend to organize into mesoscale cellular convection in the form of open and closed cells. Although COAMPS credibly captures the large-scale meteorological environment, it struggles to represent fundamental properties of the boundary layer, including inversion strength and the possibility of decoupling, necessary to form the observed cloud properties. The model produces post-frontal clouds associated with grid-scale updrafts, which appear to be the model’s attempt to represent mesoscale organization of cellular convection. However, the simulated clouds are mostly too thick, with too much liquid water and too little cloud-base drizzle. Moroever, the open cells are small and unorganized. The system-relative analysis framework of compositing cloud and boundary-layer properties on the cold front serves as an innovative approach to model verification. Our results have yielded new insights into the evolution of boundary-layer and cloud properties over different regions of a synoptic cyclone, with special focus on the mode of mesoscale organization over the post-cold-frontal zone.

Grantor dc:publisher

University of Kansas

Year dc:date.issued

2025

Author dc:creator

• Eissner, Jordan

Advisor dc:contributor.advisor

• Mechem, David B.

• Atmospheric sciences
• Clouds
• Extratropical Cyclone
• Modeling
• Synoptic
• Validation

Statement dc:rights

• This item is protected by copyright and unless otherwise specified the copyright of this thesis/dissertation is held by the author.

Language dc:language.iso

en

Dc Identifier Other

https://www.proquest.com/LegacyDocView/DISSNUM/32167377

OAI identifier oai:identifier

oai:kuscholarworks.ku.edu:1808/37904