Presenter:  Richard D. Clark, Dept. Chair and Professor of Meteorology, Millersville University

Abstract: Observations of the Great Plains low level jet on the nights of 10, 20, and 22 June 2015 during the Plains Elevated Convection At Night (PECAN) field experiment provide an opportunity for detailed investigation of the differences between weak (13 m/s), medium (23 m/s), and strong (33 m/s) jets, and the underlying structure and evolution of the nocturnal boundary layer (NBL). Measurements were obtained during June-July 2015 using the Millersville University Atmospheric Research and Aerostat Facility (MARAF), an integrated observing system deployed in Ellis, KS (FP3), one of six sites making up the Fixed PECAN Integrated Sounding Array (Fixed-PISA; FP). MARAF is an integrated observing system that includes a rawinsonde system, tethered balloon system, flux tower, acoustic sodar with RASS extension, and lidar. During LLJ IOPs, radiosondes were launched every 30 minutes starting at 0000 UTC or earlier to capture the formation, evolution, and dissipation of the LLJ. While observations support the dominating characteristics of conceptual models (e.g. Blackadar and Holton) that reasonably describe the body forces and ageostrophic velocity field, significant variability across the synoptic and mesoscale domains ensure that no two LLJs are alike. Three case studies are presented here to illuminate the influence that local and regional gradients can have on the structure and behavior of the boundary layer winds.