Thu, 28 Jan 2016 11:00:00 CST — by: Callie Oldfield
This study specifically focused on diurnal influences of the Plateau on cloud base heights and atmospheric mixing depths, and was conducted with the US Forest Service, Department of Physics, and the assistance of the Office of Environmental Stewardship and Sustainability.
Clouds located near the earth’s surface are most affected by the diurnal cycle of temperature and compression of winds over complex terrain. Over the course of a day, the temperature peaks in the afternoon and drops at night, so that the earth’s surface may cool more quickly than higher layers in the atmosphere. This results in an inversion of the temperature, which affects cloud formation and structure. This can result in the famous Sewanee fog. Topography, such as mountains and valleys, can also lead to more frequent inversions. Furthermore, the mixing height, the height at which a pollutant can be dispersed into the sky, is greatly decreased during an inversion.
Last summer, with the guidance of adviser Dr. Randolph Peterson (Physics), Scott Goodrick (USDA Forest Service), and the help of Kevin Hiers (Office of Stewardship and Sustainability), Joel measured the cloud base heights up to 25,000 feet above the Cumberland Plateau using specialized equipment called a laser celiometer. He was most interested in seeing how the slope of the Cumberland Plateau would affect the cloud mixing height and compared results to forecasted predictions.
After taking cloud base heights five different points from the top to the bottom of the Cumberland Plateau, Joel found that cloud mixing heights were, on average, less than the predicted values. The team postulates that this may be a result of model's overestimating plateau's topographic interaction with prevailing winds on warm summer days, in which the mixing heights are high relative to the Plateau. Results when published will help improve weather forecasts and transport modeling of smoke or other pollutants.
Joel Stewart graduated from Sewanee in December 2015 and is currently continuing his research as an intern with the Forest Service.