Development and forcing of the rear inflow jet in a rapidly developing and decaying squall line during BAMEX

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 (delta P-B), 2) the dynamic pressure gradient induced by the circulation between the vortices (delta P-V), 3) the dynamic irrotational pressure gradient (delta P-I), and 4) the background synoptic-scale dynamic pressure gradient (delta P-S).

During the formative stage of the bow, delta P-I was the strongest forcing mechanism, contributing 50% to the rear inflow. However, during the mature and weakening stages, delta P-I switched signs and opposed the rear inflow while the combination of delta P-B and delta P-V accounted for at least 70% of the rear inflow. The delta P-S forced 4%-25% of the rear inflow throughout the system evolution.