Advances in Supercell Storm Research

Supercells are the most severe and long-lasting type of highly organized convective storms, representing the most well-organized form with the greatest potential for causing disasters and a high likelihood of producing extreme weather events. This article provides a comprehensive overview and recent highlights of supercell research, including the unique structure, environmental characteristics, and the formation and maintenance mechanisms of the mesocyclone. Buoyancy instability is a necessary ingredient of the supercell's environment, whereas dynamic factors such as vertical wind shear and low-level storm-relative helicity are more sensitive parameters for distinguishing supercells from non-supercells. The near-storm environmental parameters derived from multi-sensor observations are expected to enhance high-resolution nowcasting of supercell storms. Supercells of different types, as well as those responsible for different hazardous weather, exhibit distinct characteristics in reflectivity morphology and in their dynamical and microphysical structures. For instance, tornadic supercells have a strong low-level mesocyclone, while severe hail supercells feature a strong and deep mesocyclone. Mesocyclones associated with damaging winds are accompanied by significant mid-level radial convergence, while those responsible for heavy precipitation typically located at low levels. The vertical vorticity of mesocyclone comes from the tilting of environmental horizontal vorticity by intense updrafts related to storms. The horizontal vorticity that tilts into the mid-level mesocyclone originates from the environmental vertical wind shear (where wind direction and speed vary with height) producing the horizontal vorticity along the inflow to the storms. In contrast, the horizontal vorticity that tilts into the low-level mesocyclone has two distinct origins: one is associated with low-level environmental vertical wind shear, while the other is produced by baroclinicity near the gust fronts. It is currently unclear which mechanism is more reasonable or dominant. Moreover, the maintenance and enhancement mechanisms of the mesocyclone are complex and diverse in situations such as the mesocyclone being surrounded by heavy precipitation, storm mergers, and the presence of mesoscale boundaries (fronts, dry lines, gust fronts, etc., and their associated convergence lines) near the surface. In recent years, based on super high-resolution numerical experiment results, the physical conceptual models of the supercell tornadogenesis have been updated. New microphysical and dynamic characteristics have been revealed by the polarimetric Doppler weather radar observation, enabling more accurate detection of hail sizes. However, the refined physical conceptual model of severe hail growth still requires improvement, and our understanding of the formation mechanisms of extreme wind gusts and flash floods associated with supercells remains limited.