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With around 40% of the world’s population living within 100 km of a coastline, and approximately 55% of the world’s population living in urban environments (a number that is expected to increase over the next decades), weather phenomena affecting coastal cities can be among the most impactful to Earth’s inhabitants.  Many of the nation’s most populous cities, including New York, Los Angeles, Chicago, Houston, Miami, Philadelphia, San Francisco, Boston, and Baltimore, are situated in complex coastal environments that result in rapidly changing and difficult-to-predict weather conditions.  Such weather conditions can unsettle the lives and activities of people in and around these cities, and can include extreme precipitation, significant temperature gradients, and sudden wind directions that can transport and localize pollution and reduce air quality. 

To help advance understanding of some of these complex meteorological regimes and their impacts, the University of ŷ���ڱ���Ƶ Boulder’s Integrated Remote and In Situ Sensing (IRISS) team has been deploying robotic aircraft to the skies around some of these cities to collect information on temperature, winds, humidity, and atmospheric particulate matter.  These slow-flying aircraft can collect detailed information that helps scientists and weather model developers improve understanding of key phenomena, including sea and lake breezes, the urban “heat island”, urban and industrial pollution, and more.

In 2021, the team deployed to coastal Wisconsin, operating their RAAVEN aircraft along the coastline of Lake Michigan to understand how coastal weather can combine with pollution from heavily populated areas in and around Chicago to negatively impact air quality in rural regions downstream.  Flying from the , just north of the Wisconsin-Illinois border, the RAAVEN observed numerous lake breeze circulations and the associated ozone pollution levels as part of a project titled “Wisconsin’s Dynamic Influence of Shoreline Circulations on Ozone ().  The lake breezes, driven by the strong temperature gradient between the warm land surface and cold Lake Michigan waters in spring and early summer, acts as a conveyor belt for gasses and pollution that have been blown to the north from greater Chicago and industrial areas like Gary, Indiana.  Working with collaborators from the University of Wisconsin Eau-Claire (a primarily undergraduate institution, or PUI) and Purdue University, the RAAVEN team collected data to demonstrate how turbulence and atmospheric layering drive where the highest concentrations of ozone end up.  These concentrated ozone layers can cause significant health impacts for local inhabitants of this region which has seen regularly-elevated levels of ozone because of this phenomenon.

Following up on this work, the RAAVEN team next headed to Texas to participate in the TRacking Aerosol-Convection interactions ExpeRiment (), a US Department of Energy led effort focused on the interplay between coastal and urban regions and the ultimate impact on clouds and precipitation.  As part of a of TRACER dedicated to the operation of uncrewed aircraft systems (UAS) IRISS conducted over 130 flights over the summer of 2022, collecting detailed measurements of atmospheric development, sea and bay breezes, and particulate matter concentrations.  The latter is particularly important as the TRACER project had few sources of information on the spatial and vertical structure of aerosol concentrations, which can have significant implications for human health and cloud and precipitation development.  Working with partners from several US Department of Energy national laboratories, the University of Oklahoma, the University of Houston, and others, TRACER data from the RAAVEN is currently being analyzed to help improve our fundamental understanding of the development of convection and extreme precipitation around Houston. 

Looking ahead, the IRISS team is currently working with collaborators at Argonne National Laboratory to provide vertical and spatial information on atmospheric conditions in the city of Chicago as part of the Community Research on

Climate and Urban Science () project which aims to be responsive to the needs of a diverse set of communities in the greater Chicago urban area.  Operating in this area comes with some unique challenges due to the busy airspace and generally built-up environment.  However, the lower atmosphere over cities is a generally under-sampled environment due to a lack of infrastructure and drones and other robotic platforms offer unique capabilities for capturing unique and innovative information in these areas.  As a result, IRISS will continue to seek out opportunities to sample such environments, including in connection with DOE’s other , and advance our technological capabilities to be able to meet the needs of urban sampling.  Capturing such information will play a central role in understanding these unique environments that lie at the heavily-populated intersection of city and coastline over the coming decades.