The Development of Atmospheric Bores in Non-Uniform Baroclinic Environments and Their Roles in the Maintenance, Structure, and Evolution of an MCS

This study used radar observations and a high-resolution numerical simulation to explore the interactions between an mesoscale convective system (MCS), cold pool outflows, and atmospheric bores in a non-uniform baroclinic environment. The bores were generated by a nocturnal MCS that occurred on 2-3 June 2017 over the southern North China Plain. The goal of this investigation is to determine how the structure of bores varied within this non-uniform environment and whether and how the bores would maintain the MCS and alter its structure. To the southwest of the MCS, where there was large CAPE and a well-mixed boundary layer, discrete convection initiation occurred behind a single radar fine line (RFL) maintaining the propagation of the MCS. To the southeast of the MCS, multiple RFLs were found suggesting the generation of an undular bore in an environment containing an intense nocturnal stable boundary layer with dry upper layers and little CAPE. Hydraulic and nonlinear theory were applied to the simulation of the MCS revealing that the differences in the bore evolution depended on both the characteristics of the cold pool and the variations in the ambient environment. Thus, the characteristics of the ambient environment and the associated differences in bore structure impacted the maintenance and organization of the MCS. This study implies the importance of an accurate representation of the low-level ambient environment and the microphysics and kinematics within the MCS to accurately simulate and forecast cold pools, the generation and evolution of bores, and their impact on nocturnal MCSs. Convective storms that occur during the day are often maintained by the lifting of low-level air by storm outflows. At night when a low-level stable layer forms, these outflows can generate an atmospheric bore, which is a type of gravity wave response. Investigations at numerous locations worldwide have demonstrated that bores contribute to the initiation and maintenance of nocturnal convective systems. However, relatively few studies have concentrated on how a non-uniform nocturnal environment can change the structure of bores and their impact on convection. This study examines how bores and convection interact over the southern North China Plain (SNCP) where the nocturnal environment during warm season is often non-uniform. These environmental variations impacted the generation and evolution of the bores altering the storm structure. The bores over the SNCP also had a unique generation mechanism forming when a strong downdraft penetrated into a moist layer. This study shows that an accurate representation of both the ambient environment and the storm microphysics and kinematics are likely necessary to improve the forecast accuracy of the nocturnal convective systems, particularly over regions with a non-uniform environment, such as the SNCP. Atmospheric bores are generated within a nocturnal mesoscale convective system in a non-uniform environmentThe mesoscale variations in the environment ahead of the mesoscale convective system (MCS) modify the structure of the bores, which impact the organization of the MCSThe intrusion of the convective downdraft into the nocturnal boundary layer plays a critical role in generating bores over the southern North China Plain