Self-Organization and Maintenance of Simulated Nocturnal Convective Systems from PECAN

Abstract

AbstractThe Plains Elevated Convection at Night (PECAN) field project was designed to explain the evolution and structures of nocturnal mesoscale convective systems (MCSs) and relate them to specific mechanisms and environmental ingredients. The present work examines four of the strongest and best-organized PECAN cases, each numerically simulated at two different levels of complexity. The suite of simulations enables a longitudinal look at how nocturnal MCSs resemble (or differ from) more commonly studied diurnal MCSs. All of the simulations produce at least some surface outflow (“cold pools”), with stronger outflows occurring in environments with more CAPE and weaker near-ground stability. As these surface outflows emerge, the lifting of near-ground air occurs, causing each simulated nocturnal MCS to ultimately become “surface-based.” The end result in each simulation is a quasi-linear convective system (QLCS) that is most intense toward the downshear flank of its cold pool, with the classical appearance of many afternoon squall lines. This pathway of evolution occurs both in fully heterogeneous real-world-like simulations and horizontally homogeneous idealized simulations. One of the studied cases also exhibits a back-building “rearward off-boundary development” stage, and this more complex behavior is also well simulated in both model configurations. As a group, the simulations imply that a wide range of nocturnal MCS behaviors may be self-organized (i.e., not reliant on larger-scale features external to the convection).