High-Pressure Systems Favor Sea-Breeze Convection Over Southeastern Texas

The Science

During the summer months, sea- and bay-breeze circulations from the Gulf of Mexico and Galveston Bay are important drivers of the weather in southeastern Texas. These circulations, in conjunction with those from larger-scale weather systems—also known as the synoptic conditions—affect the flow of moisture and aerosol particles into the Houston region. This affects the development of thunderstorms and their associated rainfall. Understanding how these flows effect clouds and storms is important to improving models used for weather forecasts and climate predictions.

The Impact

This study uses artificial intelligence techniques to reveal the relationships between weather system circulations and cloud physics in southeastern Texas. The findings include key insights into the variability of these circulations in the region. This helps researchers isolate the effects of circulations on features of the region’s climate, such as how storms form, the impact of aerosols, and other factors. These insights are helping researchers narrow the focus of their study of aerosol and cloud life cycle, aerosol-cloud interactions, and air quality during the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) user facility’s TRacking Aerosol Convection interactions ExpeRiment (TRACER) field campaign in the Houston area in 2021 and 2022.

Summary

This research classified synoptic regimes during the summer months (June-September) in the southeastern Texas region using Self-Organizing Map (SOM), an unsupervised machine learning approach. The team included scientists from Brookhaven National Laboratory, Pennsylvania State University, Purdue University, SUNY Geneseo, Stony Brook University, and Cornell University. They applied the SOM to 10 years of 700-hPa geopotential height anomalies from reanalysis data to distinguish three dominant synoptic regimes, with a continuum of transitional states between them. The primary regimes include: (1) a pre-trough regime associated with a synoptic trough to the northwest of the region, (2) a post-trough regime with upper-level northerly flow, and (3) an anticyclonic regime within the westward extent of the Bermuda High.

The team projected data from the Geostationary Operational Environmental Satellite and the Next-Generation Weather Radar system onto each SOM node to investigate the characteristics of cloud and precipitation properties (e.g., fraction, intensity) in different regimes. When southeastern Texas is positioned to the southwest quadrant of a maritime high-pressure system, the region experiences increased cloud frequency during the afternoon hours due to significant moisture advection. This regime commonly includes a confluence of synoptic southerly flow and sea-breeze circulation. When a high-pressure system is over southeastern Texas, the area is dominated by large-scale subsidence with weak pressure gradients and moderate precipitable water vapor. This weak synoptic forcing is favorable for sea-breeze formation. This is confirmed by an enhanced onshore flow and a decreased temperature at the surface in the early afternoon, as well as a sharp increase in radar echo top height. 

Funding

This research was funded by the DOE Office of Science, Biological and Environmental Research program and Office of Workforce Development for Teachers and Scientists.