Simulated convective lines with leading precipitation. Part II: Evolution and maintenance

摘要

This article, the second of two describing a study in which the authors used idealized numerical simulations to investigate front-fed convective lines with leading stratiform precipitation (FFLS systems), addresses the dynamics and sensitivities governing the systems' evolution toward other structures and their sustenance despite the apparent contamination of their inflow by preline precipitation. Sensitivity tests show that the middle- and upper-tropospheric wind shear are important to the updraft tilt and overall structure of the simulated systems. In time, simulated FFLS systems tend to evolve toward a convective line with trailing stratiform (TS) precipitation structure because they tend to decrease the line-perpendicular vertical wind shear nearby. This, along with gradual increases in the system's cold pool strength, contributes to more rearward-sloping updrafts and may initiate a positive feedback mechanism that hastens transition toward TS structure. However, whereas the system's tendency to decrease the local shear favors the demise of the FFLS mode, the presence of precipitation on its line-leading side actually favors its maintenance. FFLS systems are able to destabilize their own inflow in the preline precipitation region owing to the vertical profile of evaporation and melting and to lifting, a feature that is quite robust in the simulations. The authors conclude this second article with a general restatement of FFLS dynamics based upon synthesized results from the pair of papers.