Development and Forcing of the Rear Inflow Jet in a Rapidly Developing and Decaying Squall Line during BAMEX

Abstract

This study examines the development, structure, and forcing of the rear inflow jet (RIJ) through the life cycle of a small, short-lived squall line over north-central Kansas on 29 June 2003. The analyses were developed from airborne quad-Doppler tail radar data from the NOAA and NRL P-3 aircraft, obtained over a 2-h period encompassing the formation, development, and decay of the squall line during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). The strengthening of the system-relative rear inflow to 17 m s 21 was concurrent with the formation of a bow echo, an increased dynamic pressure gradient beneath the rearward-tilted updraft, and two counterrotating vortices at either end of the bow. The later weakening of the RIJ to 8 m s 21 was concurrent with the weakening of the bow, a decreased dynamic pressure gradient at midlevels behind the bow, and the weakening and spreading of the vortices. In a modeling study, Weisman quantified the forcing mechanisms responsible for the development of an RIJ. This present study is the first to quantitatively analyze these mechanisms using observational data. The forcing for the horizontal rear inflow was analyzed at different stages of system evolution by evaluating the contributions of four forcing mechanisms: 1) the horizontal pressure gradient resulting from the vertical buoyancy distribution (dP B ), 2) the dynamic pressure gradient induced by the circulation between the vortices (dP V ), 3) the dynamic irrotational pressure gradient (dP I ), and 4) the background synoptic-scale dynamic pressure gradient (dP S ). During the formative stage of the bow, dP I was the strongest forcing mechanism, contributing 50% to the rear inflow. However, during the mature and weakening stages, dP I switched signs and opposed the rear inflow while the combination of dP B and dP V accounted for at least 70% of the rear inflow. The dP S forced 4%-25% of the rear inflow throughout the system evolution.

Mesovortices within the 8 May 2009 Bow Echo over the Central United States: Analyses of the Characteristics and Evolution Based on Doppler Radar Observations and a High-Resolution Model Simulation

“…Various factors have been implicated in the development of RIJs, such as the hydrostatically induced midlevel pressure minimum behind the leading convective updrafts (Lafore and Moncrieff 1989), horizontal buoyancy gradients related to the upshear-tilting convective circulation (Weisman 1992(Weisman , 1993, and bookend (or lineend) vortices (Skamarock et al 1994;Weisman and Davis 1998;Grim et al 2009;Meng et al 2012). Additionally, the RIJ strength had been found to be sensitive to ice microphysical processes as well as the environmental humidity (Yang and Houze 1995;Mahoney and Lackmann 2011).…”

Observations of Elevated Convection Initiation Leading to a Surface-Based Squall Line during 13 June IHOP_2002

“…There are several studies of systems that have made the transition from surface-based to elevated Wetzel et al 1983;Bernardet and Cotton 1998;Bernardet et al 2000) and of cold-pool formation from elevated systems (Trier et al 2006); such transitions are known to be important for the evolution of convection (e.g., Parker 2008). There are, however, very few studies of the transition from elevated to surface-based convection (e.g., Trapp et al 2001;Bryan and Weisman 2006;Corfidi et al 2008;Grim et al 2009). …”

Microphysical and Thermodynamic Structure and Evolution of the Trailing Stratiform Regions of Mesoscale Convective Systems during BAMEX. Part II: Column Model Simulations

“…Smith et al (2009, hereafter Part I) expanded the work of MF07 by using airborne Doppler radar observations and level II Weather Surveillance Radar-1988 Doppler analyses to examine the meteorological context of the observed microphysical and thermodynamic structures. A fourth paper, Grim et al (2009), presents high-resolution multi-Doppler observations of the entire life cycle of a squall line within the 29 June 2003 MCS and investigated the forcing mechanisms for the development and intensification of the RIJ associated with this squall line.…”