Observations of Wave-turbulence Interactions Impacting the Stable Boundary Layer Over Central Pennsylvania

Open Access
Suarez Mullins, Astrid
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 21, 2013
Committee Members:
  • David R Stauffer, Thesis Advisor
  • terrain-induced gravity waves
  • rotors
  • downslope windstorm
  • stable boundary layer
The impact of wave-turbulence interactions in the stable boundary layer is investigated using observations from a special observing network located at Rock Springs, PA. Internal gravity waves can affect the evolution and destruction of valley cold pools and produce intermittent turbulence through the modification of momentum and thermal fluxes and nonlinear phenomena (such as wave breaking or rotors). Thus, their study is crucial for improving air quality modeling and hazard predictions under stable conditions. Six cases, characterized by nonstationarity and complex, near-surface circulations in the stable boundary layer, are identified during the spring-fall season of 2011. These cases include three synoptic regimes for which gravity waves are hypothesized. The first regime is characterized by westerly or northwesterly flow and trapped gravity waves excited by the Allegheny Mts. The second regime is characterized by a strong southerly wind component and trapped lee waves excited by Tussey Ridge. Finally, the third regime is characterized by southerly flow, weak synoptic forcing and weak near-mountain-top shear. Network measurements for the third regime suggest the presence of downslope windstorm-like motions. Observational evidence for the existence of two types of wave-turbulence interactions, resembling that of Type 1 (associated with trapped waves) and Type 2 (associated with hydraulic-jump type events) rotor circulations, impacting the Rock Springs network are presented. It is also shown that periods of warming are typically associated with downward motion, reduced Richardson number, enhanced turbulence, positive vertical heat flux and large directional shifts (up to 180º). The largest temperature and wind speed fluctuations are associated with cases hypothesized to have the strongest nonlinear behavior. Analysis of 2-m turbulence confirms that the Richardson number is not a good measurement of stability for cases characterized by gravity wave activity. Turbulence and positive vertical heat fluxes are observed during periods when Richardson number is much greater than 1. In this study, observational evidence of the presence of complex wave-turbulence interactions generated by moderately complex topography (<300 m AGL) is presented. This work provides the foundation for the investigation of wave-turbulence interactions in the stable boundary layer using high resolution numerical models for real-data cases.