Shallow thermally-driven wind circulations commonly develop along extensive coastlines, across which horizontal gradients in solar absorption, evaporation and resultant sensible heating rates are often quite large. Associated sea breeze development along extensive (and generally stationary) coastlines bordered by flat terrain has been well described. These circulations modulate surface air temperatures and boundary-layer mixing, and thus impact both meteorology and air quality in the coastal zone. Less well understood are the structure and dynamics underlying lake-breeze formation in the presence of steep orography and/or variable coastline location, as prone to occur owing to fluctuation of water levels in runoff-fed lakes within arid regions. Such is the situation for the Great Salt Lake (GSL), which is bordered by the major urban area of Salt Lake City and has undergone marked changes in water level and associated projection of its coastline over the past decade. Prior work has described the rudiments of GSL lake breeze formation, including statistics of its frequency and preferred seasonality, but have been confined mainly to a two-dimensional (surface-based) perspective.
This new study will (1) analyze archived observations over a 10-year period, which include data from a relatively dense surface mesonetwork ('MesoWest', and its predecessor the 'Utah Mesonet') and a terminal Doppler weather radar (TDWR) site, to develop a more complete 3D climatology of GSL lake-breeze behavior; (2) collect and analyze both routine and special observations (including aforementioned radar based views of low-level airflow, wind and thermodynamic profiles from two mobile balloon-launch platforms, and selectively positioned measurements from up to eight portable surface meteorological stations) to examine ~10 lake-breeze events during Autumn 2008; and (3) apply a combination of large-eddy simulation (LES) and more traditional mesoscale simulations using WRF (the Weather Research and Forecasting model) to explore the response of these circulations to variations in surface heating induced by varying lakeshore extent and large-scale forcing.
The intellectual merit of this work rests in advancing our basic understanding of thermally-driven circulations along coastlines in the presence of nearby steep terrain, and increased knowledge of processes that control the development of lake breezes in arid environments. It will also provide a detailed description of some of the complex interrelationships between regional-scale weather and the GSL ecosystem, and better quantify potential sensitivity of atmospheric circulations to both natural and anthropogenic changes in the underlying surface state.
Broader impacts of this work will include contributions toward more accurate simulation of local/regional weather and impacts on urban meteorology in densely populated coastal zones (including, for example, daily maximum temperature forecasts impacting energy demands and changes in ventilation/mixing impacting air quality). Training of a graduate student and postdoctoral research associate in the design and execution of coordinated LES and traditional mesoscale simulations will be supported, as will involvement of up to 20 undergraduate students to be directly involved in planning and conducting field data collection in the vicinity of lake-breeze fronts adjacent to the GSL.
Degradation of coastal air quality will increasingly stress human health as three-quarters of the worldâ€™s population is projected to be within coastal areas by 2030. Sea and lake breezes, which are driven by the temperature contrasts between the water and surrounding land surfaces, help modulate air quality in coastal zones. Our study of sea land lake breezes began with an extensive review of the work completed over the past several decades on simulating them. We conducted as well two field campaigns (one during summer and another during winter supported primarily by a separately funded NSF project) that involved dozens of undergraduate and graduate students to collect observations near the shores of the Great Salt Lake, the fourth largest terminal lake in the world. These observations are particularly relevant for understanding sea and lake breeze evolution in the rarely-studied arid environments of the world. Building on the literature review, we also applied a very high resolution model to determine the sensitivity of sea and lake breezes to variations in the heating over nearby land surfaces and the stability of the atmosphere. Our analysis is the first to explore the effects of land surface heating and stability on the characteristics of lake breezes. We found that the horizontal wind speed and inland extent of the sea breeze are largely controlled by the surface heating, while the sea-breeze depth is controlled by stability as well. Lake-breeze circulations develop similarly to sea-breeze circulations through mid-morning but weaken significantly in the afternoon and there is no afternoon acceleration of the inland-moving lake-breeze front as there often is for sea breezes.