Establishing a Holistic Understanding of the Circulations of Mesoscale Convective System Stratiform Regions

Description

The ability to simulate MCS stratiform regions that closely match observations remains elusive. The issue is further complicated because the characteristics of the stratiform region are closely tied to the detrainment of hydrometeors from the convective updraft as well as evaporation and sublimation induced by mid-level rear inflow. These intra- and extra-system circulations are products of three processes: low-frequency gravity waves, line-end vortex-induced flows, and environmental wind. While these processes ultimately control the characteristics of the stratiform region, their individual contributions to the MCS wind field have not been formally quantified.

We hypothesize that the poor representation of MCS stratiform regions in model simulations is a result of an incorrect balance between gravity wave, line-end vortex, and environmentally induced flows that results from an incorrectly simulated latent heating profile. The ARM-supported PECAN and MC3E field campaigns offer unprecedentedly detailed low-level observations coincident with multi-Doppler storm wind field characterization so that quantification of these individual contributions is now possible. To test this hypothesis, our project focuses on three objectives: (1) Identify low-frequency gravity waves generated by midlatitude MCSs observed by the PECAN and MC3E field campaigns; (2) Isolate the impacts of low-frequency gravity waves, line-end vortex, and large-scale environmental flows on the development and characteristics of the observed PECAN and MC3E MCS stratiform regions; and (3) Identify potential errors in the stratiform region of LES-simulated PECAN and MC3E MCSs resulting from incorrect circulation causal partitioning compared to (2).       

The first two objectives use PECAN and MC3E datasets, including lower-tropospheric AERI and profiler observations, in situ and remotely sensed microphysical observations, and multiple-Doppler-derived three-dimensional wind fields to identify low-frequency gravity waves, line-end vortices, the environmental wind field, and their associated circulations. Preliminary identification of some of the low-frequency gravity waves observed within the 20 May 2011 MC3E and 15 July 2015 PECAN case datasets are presented. Future work will analyze the stratiform region microphysical modifications associated with these waves.