13.6 MCS Propagation Mechanisms Observed during the PECAN Field Campaign

Wednesday, 5 August 2015: 12:00 AM
Republic Ballroom AB (Sheraton Boston )
Anthony W. Lyza, Univ. of Alabama in Huntsville, Huntsville, AL; and K. R. Knupp

One primary focus of the 2015 Plains Elevated Convection at Night (PECAN) field campaign is the formation and maintenance of nocturnal mesoscale convective systems (MCSs) in the central Great Plains of the United States. Classical MCS understanding closely relates MCS structure to the structure of a density current, in which the propagation of an MCS is largely driven by the buoyancy deficit of the cold pool relative to the environment ahead of the MCS. For nocturnal MCSs, however, the magnitude of this deficit is hindered by stabilization during the development of the nocturnal boundary layer (NBL), which theoretically limits density current (and MCS) propagation. However, fast-moving nocturnal MCSs associated with severe convective weather (i.e. damaging downdraft/downburst winds and occasionally tornadoes) are not rare. In addition to density currents, bores and solitary waves are two commonly observed nocturnal MCS propagation mechanisms. Destabilization associated with a bore, due to mixing, and additional mechanical lift by a bore or a solitary wave can enhance the propagation of a nocturnal MCS. Additionally, bore-driven MCSs tend to develop convection that is not rooted completely above the stable nocturnal boundary layer but rather near the top of the boundary layer, approximately 200-400 m AGL. Although the only slightly-elevated nature of the convection associated with these MCSs may seem to increase the potential for the previously-mentioned hazardous weather impacts, the exact nature of bore-driven or solitary-wave-driven MCSs is not well-understood. In this presentation, we overview MCS propagation mechanisms observed during the PECAN field campaign, using ground-based remote sensing and in-situ observational platforms to diagnose MCS structure, speed, and thermodynamic profile modification. These preliminary results are used to form a contextual frame of reference for in-depth analysis of nocturnal MCS propagation in various nocturnal environments.
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