Dynamic instability in the planetary boundary layer over the arid land
McCauley, Steven D
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Classic baroclinic theory is one of the most significant findings of modern meteorology and has often been used to investigate the nature of wave-like disturbances introduced onto a mean flow field. The theory provides an elegant explanation for the propagation speed, structure, growth and decay of the predominant synoptic-scale (approximately 4000 km in zonal wavelength) weather systems observed in the middle latitudes. However, not all major disturbances in the atmosphere possess a synoptic-scale wavelength. Subsynoptic-scale (1000 - 2000 km in zonal wavelength) disturbances are often found in the lower troposphere over arid land during the summer months. These disturbances appear to originate in a deep and neutrally stratified planetary boundary layer (PBL) of relatively mild horizontal thermal gradient. The deep neutral layer is caused and maintained by intense surface heating. When these shortwave disturbances encounter potentially unstable air, they can trigger intense convective events. Unfortunately, classic baroclinic theory cannot be used to describe the behavior of these systems. This study is a mathematical analysis of the governing equations of motion in order to account for the genesis and maintenance of these unique PBL disturbances. The goal of the analysis is to provide a better understanding of the dynamics of these shortwave disturbances in order that further improvement in the numerical weather prediction of these systems and their consequences can be achieved.