Simulated Convective Lines with Leading Precipitation. Part I: Governing Dynamics

Abstract

This article, the first of two describing a study in which the authors used idealized numerical simulations to investigate convective lines with leading precipitation, addresses the dynamics governing the systems' structures and individual air parcels' accelerations within them. It appears that, although unconventional, systems with inflow passing through their line-leading precipitation can be stable and long lived. Lower-tropospheric inflowing air in the simulations ascends, overturns in deep updrafts, and subsequently carries its water content forward from the convective line, where it gives rise to the leading precipitation region. Although relatively strong wind shear in the middle and upper troposphere accounts for a component of the downshear acceleration, and hence overturning, of air parcels in the simulated updrafts, a mature system with leading precipitation also renders both persistent and periodic pressure anomalies that contribute just as much. Many of these accelerations, which govern the overall system structure, are largely transient and are lost when averaged over multiple convective cycles. This article explains the dynamics that govern the transient updrafts and downdrafts within the systems, including a precipitation cutoff mechanism that governs their multicellular periods.