Matt Parker
University of Nebraska--Lincoln

ABSTRACT

"Structures and Dynamics of Mid-latitude Mesoscale Convective Systems"

 

Mesoscale convective systems (MCSs) have great impact on our society, producing much of the growing season rainfall in the agriculturally vital Great Plains, as well as widespread hazardous weather. Although convective lines with trailing stratiform (TS) precipitation have been widely established as a recurring mode of MCS organization, recent work has revealed that approximately 20% of the linear MCSs in the central United States have leading stratiform precipitation and about 20% have parallel stratiform precipitation. Because the LS and PS structures occur in unique environments and have unique lifetimes and motion speeds, they are relevant to flash flood forecasting. Three common quasi-2D MCS flow structures will be reviewed: front-fed (sustained by front-to-rear storm-relative inflow) TS and LS systems, as well as rear-fed (sustained by rear-to-front storm-relative inflow) LS systems. The governing dynamics revealed by simulations of these three archetypes will be discussed, with particular attention paid to the front-fed LS mode. In these systems, lower tropospheric inflowing air 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. Significantly, it appears that, although unconventional, systems with inflow passing through their line-leading precipitation can be stable and long-lived. Front-fed LS systems are able to destabilize their own inflow in the pre-line precipitation region owing to the vertical profile of evaporation and melting and to lifting. In addition to describing the parcel dynamics responsible for the front-fed LS structure, ongoing work on PS MCSs and convective organization in moderate-to-high shear regimes will also be discussed.