Characterizing the effects of convection on the afternoon-to-evening boundary layer transition during PECAN 2015

Abstract

The Great Plains exhibits a widely known characteristic transition in the atmospheric boundary layer, from a daytime unstable boundary layer to a nocturnal stable boundary layer near sunset. There remains much to learn about this process through observational data. Impacts of convective weather prior to and during this transitional period is one of the lesser understood subjects. During the Plains Elevated Convection at Night (PECAN) field campaign from June 1 to July 15, 2015, extensive measurements of near surface thermodynamic variables, wind speed and direction, turbulence and scalar perturbations were made outside the city of Greensburg, Kansas. These measurements were made on three towers: a 16-m flux tower, 6-m flux tripod, and a 3-m scaler tripod, giving 17 levels of measurement from 25 cm below the surface to 16 m above. To supplement the tower-based measurements, a Leosphere Doppler LIDAR and a sonic detection and ranging (SODAR) device were used to obtain vertical profiles of mean wind and turbulence up to approximately 250 m and 6000 m, respectively. The primary focus of this thesis is to characterize the transitional period with the presence of convective events. This thesis also used the observed surface fluxes to evaluate the fluxes calculated from the bulk parameterization scheme. The surface layer stability functions in the Coupled Air Ocean Response Experiment (COARE) surface flux algorithm will be used. The surface roughness used in the Navy's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) model will also be examined.