Structures and Dynamics of Quasi-2D Mesoscale Convective Systems

Abstract

Recently, three distinct archetypes for midlatitude linear mesoscale convective systems (MCSs) have been identified. This article focuses on the fundamentals of two of these archetypes: convective lines with trailing stratiform (TS) precipitation and convective lines with leading stratiform (LS) precipitation. Both the TS and LS modes typically exhibit quasi-2D reflectivity patterns and quasi-2D environmental storm-relative wind fields. Ongoing work has revealed that there are three common flow structures for these quasi-2D MCSs: front-fed TS systems (which are sustained by front-to-rear storm-relative inflow), as well as front-fed LS and rear-fed LS systems (which are sustained by rear-to-front storm-relative inflow). This paper summarizes the observed structures of the front-fed TS, front-fed LS, and rear-fed LS modes, and then outlines an idealized numerical experiment in which these modes were simulated. The authors analyze the basic simulated kinematic and microphysical structures and provide a framework in which to analyze the dynamics of the modeled systems. To a large degree, the organizational modes of developing quasi-2D MCSs may be anticipated by considering the magnitudes and preferred directions of the horizontal pressure gradient accelerations associated with a surface cold pool [whose strength is largely related to the environmental humidity and convective available potential energy (CAPE)] and an updraft in the mean environmental wind shear profile. In this regard, the lower-tropospheric shear is of prime importance, although the middle- and upper-tropospheric shear provide for additional, nontrivial accelerations.