Investigations of Interactions Between the Atmospheric Boundary Layer and Squall Lines

University Of Alabama In Huntsville, Huntsville AL

Investigators

Abstract

This research project will be an integral component of a multi-institution field experiment termed the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). During the field phase of BAMEX (16 May to 6 July 2003), the Principal Investigator will use the University of Alabama at Huntsville Mobile Integrated Profiling System (UAH-MIPS) to document the kinematic and thermodynamic structure of the atmospheric boundary layer (ABL) and associated squall line structure, including bow echoes and line-echo-wave patterns (LEWP). The BAMEX program seeks to improve understanding of bow echoes and associated severe weather, and mesoscale convective vortices. Specific BAMEX scientific goals include: (a) documentation of the life cycle of bow echoes, emphasizing mechanisms of damaging wind production and tornado genesis, and (b) investigation of the structure and evolution of mesoscale convective vortices that form within mesoscale convective systems. Both goals include an observational and modeling component, and the eventual goal is to improve predictability of these phenomena. The goal of this research is to advance general understanding of the interaction between the spatially variable and temporally evolving ABL and squall lines, bow echoes and LEWPs. Current knowledge of the dependence of squall line dynamics on ABL properties is not well known, particularly for the nocturnal boundary layer. During the course of this investigation, the Principal Investigator will examine the structure and evolution of squall lines and their associated ABL, which will vary from stable to unstable or neutral. Thus, detailed measurements of the thermodynamic and kinematic structure of the ABL will be acquired. A particular focus will be placed on squall line behavior and the nocturnal boundary layer. Two important problems involving interactions between squall line and ABL processes will be addressed: (a) The structure, dynamics and thermodynamics of downdrafts that produce strong surface winds within squall lines and bow echoes will be examined. (b) The development of low-level mesoscale circulations associated with development of tornadoes within squall lines will be investigated. The UAH-MIPS is ideally suited for this activity, and will be the only stationary instrument suite that can simultaneously measure detailed continuous wind profiles (up to 2-4 km AGL) and thermodynamic profiles within and above the ABL (up to 10 km AGL). Two benefits can be anticipated from this research: (a) an improved understanding of mechanisms that produce strong winds and tornadoes within squall lines, which will contribute to enhanced detection and predictability of these hazardous phenomena; and (b) comprehensive analyses that will validate numerical simulations of these phenomena, which will in turn provide future scientific advances in predictability.