Adam L. Houston
Date of this Version
Hanft, L. W., 2017: An Observational and Modeling Study of Mesoscale Airmasses with High Theta-e. M.S. Thesis, Department of Earth and Atmospheric Sciences, University of Nebraska-Lincoln.
Typically, the cool side of an airmass boundary is stable to vertical motions due to its associated negative buoyancy. However, under certain conditions, the air on the cool side of the boundary can undergo a transition wherein it assumes an equivalent potential temperature and surface-based convective available potential energy that is higher than that of the airmass on the warm side of the boundary. The resultant airmass is herein referred to as a mesoscale airmass with high theta-e (MAHTE).
Results are presented from an observational and mesoscale modeling study designed to examine MAHTE characteristics and the processes responsible for MATHE formation and evolution. Observational analysis focuses on near-surface observations of a MAHTE in northwestern Kansas on 20 June 2016 collected through multiple transects executed with an Integrated Mesonet and Tracker. The highest equivalent potential temperature is found to be 15 – 20 K higher than what was observed in the warm sector and located 2 – 5 km on the cool side of the boundary. This case was modeled using WRF-ARW to examine the processes involved in MAHTE formation that could not be inferred through observations alone. Simulations faithfully reproduce many characteristics of the observed MAHTE. Model analysis indicates that differential vertical advection of equivalent potential temperature across the boundary is important for simulated MAHTE formation. Specifically, deeper vertical mixing/advection in the warm sector reduces moisture (equivalent potential temperature), while vertical motion/mixing is suppressed on the cool side of the boundary thereby allowing largely unmitigated diurnally-driven increases in equivalent potential temperature. Model analysis also suggests that surface fluxes did not play a major direct role in MAHTE formation.
Adviser: Adam L. Houston