Francesca Lappin - November 12

School of Meteorology MS Thesis Defense

Assessing the utility of low-level buoyancy to understand atmospheric boundary layer transitions

Francesca Lappin

Friday, November 12^th

9:00 am

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Advancements in remotely piloted aircraft systems (RPAS) introduced a new way to gather in situ measurements in the atmospheric boundary layer (ABL). Adequate sampling of the lower atmosphere is key to improving numerical weather models and understanding fine-scale processes. The ABL’s sensitivity to changes in surface fluxes leads to rapid changes in thermodynamic variables. This study proposes using low-level buoyancy to characterize ABL transitions. Previously, buoyancy has been used as a bulk parameter to quantify stability. Higher-resolution data from RPASs highlight buoyancy fluctuations. RPAS profiles from two field campaigns are used to assess the evolution of buoyancy under convective and stable boundary layers. Data from these campaigns included challenging events to forecast accurately, such as convective initiation, a low-level jet, and katabatic flows. It was found that the low-level jet formed in a preexisting layer of negative buoyancy. For the case of convective initiation, the magnitude of positive buoyancy was different over a small spatial scale which appear to have impacted convection. Finally, the downslope flow caused buoyancy to evolve differently across the two sides of the valley. This study expounds on the utility of buoyancy in the ABL and contextualizes its use in comparison to Richardson number profiles. Analyzing processes in the framework of buoyancy allows for impacts from moisture and temperature to be evaluated simultaneously.