Aerosol Impacts on Cloud Microphysics, Charge Structures, and Precipitation Relevant to Sea Breeze Convection

Thunderstorms occur in any given calendar month along the Texas Gulf Coast region, which is home to major urban centers such as Houston, Galveston, and Corpus Christi. Also, this area features one of the world’s most densely distributed network of refineries as well as major shipping, industrial, tourism, and medical interests. During the summer season, warm and moist air moves inland in the early afternoon as a sea breeze, which is the primary focus for the development of deep convective clouds (DCCs).

These clouds are responsible for the regular occurrence of thunderstorms and heavy precipitation that impact vulnerable populations and infrastructure due to lightning strikes and flooding. Past research has shown how aerosols derived from urban and industrial areas influence the development of DCCs, which in turn, impact the severity of lightning and precipitation associated with sea breeze thunderstorm events, demonstrating the importance of cloud invigoration by elevated levels of aerosols in this region.

However, an accurate assessment of the aerosol effects remains challenging, because of highly complex cloud charging and precipitation processes and the difficulty in representing the aerosol and cloud processes in atmospheric models.

The scientific initiative of this study takes advantage of a unique opportunity to compare and contrast the behavior of sea breeze thunderstorms which develop in polluted and clean environments along the Texas Gulf Coast region using long-term lightning, aerosol, and meteorological measurements such as temperature, pressure, humidity, and winds. The central hypothesis of this research effort is that the combination of elevated aerosol levels from various emission sources as well as favorable thermodynamic and dynamic conditions (i.e., high humidity and sea breeze lifting) renders the southeast Texas region highly susceptible to aerosol-cloud-lightning interactions.

This study will address three scientific questions: (1) What are the observational evidence and mechanisms for the impacts of aerosols derived from anthropogenic (urban/industrial/vehicle) and natural sources (e.g., agriculture and wildfire smoke) on the evolution of cloud microphysics, charge structures, and precipitation patterns of lightly-forced, warm season (June-September) sea breeze convection along the Texas Gulf Coast? (2) How can the evolution of DCCs be better constrained and simulated, in model sensitivity by inclusion of detailed aerosol, cloud condensation nuclei (CCN), ice nucleating particles (INP), and lightning parameterizations, to account for (a) clean vs. polluted conditions, (b) similar vs. variable dynamic/thermodynamic settings, and (c) continental vs. marine interface regimes? and (3) How can atmospheric models be improved for accurate simulation and quantification of aerosol-lightning-precipitation interactions by using the multiscale-resolution/multiplatform-observations provided by the recent NSF Experiment of Sea Breeze Convection Aerosols and Precipitation (ESCAPE) and DOE Tracking Aerosol Convection Interactions Experiment (TRACER) intensive observation periods, Houston Lightning Mapping Array (HLMA), stationary and mobile radar assets, aircraft, and auxiliary ground-based aerosol, cloud microphysical, meteorological, and trace gas measurements? There are four specific scientific aims in this project, including (1) climatological observation analysis of aerosol, cloud, precipitation, and lightning, (2) convective cell tracking using polarimetric radar and HLMA data, (3) assessing the impacts of CCN and INP on clouds, precipitation, and lightning using cloud-resolving models, and (4) inter-comparison between model simulations and observations with a focus on anomalous and extreme sea breeze thunderstorm cases which exhibit major lightning and flooding activity.

The analysis procedures developed in this project will lay the foundation for future applications using lightning as a key measurable quantity to assess the aerosol-cloud interaction. The modeling work will establish the relative importance of the various CCN, INP, and secondary ice processes (e.g., ice splintering/multiplication) in cloud formation, charge separation, and precipitation and will improve the representation of the mixed-phase clouds and ice processes in regional and global models.

A better understanding of the fundamental mechanisms for the aerosol microphysical effects will contribute to accurate weather forecasting and climate prediction. Outcomes from this research will be disseminated by conference presentations, media, and published journal articles to advance science. Social media outlets will be utilized in near real-time to update municipal stakeholders on the progress of this study.

Examples include highlighting lightning development and lightning safety via news/radio/internet programs, aiding first responders and emergency management officials (police/fire/rescue), and providing forensic support to areas vulnerable to rapidly changing weather and climate conditions. Moreover, the results of this research aid in supporting STEM education efforts for K-12, undergraduate, and graduate students, especially from underserved communities within the study region (e.g., Houston, Galveston, and Beaumont).

The students will benefit by establishing future connections with the broad academic/research communities in atmospheric, environmental, climate, and earth sciences.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.