Structure of a midlatitude squall line formed in strong unidirectional shear

Abstract

The orientation of the squall line, comprised of high-reflectivity centers spaced 20-40km apart, changed with time. Initially, the squall-line axis was normal to the environmental shear, but with time it became parallel to the shear vector, as the northeastern portion of the subcloud cold dome merged with cold air generated by individual storms that had formed ahead of the line. The intensity of the cells within the squall line diminished as its axis became more parallel to the shear. The persistence of squall-line elements is discussed in light of a) their resemblance to supercells as represented in numerical simulations, and b) recent theories involving the balance of vorticity between vertical shear in the low-level environment and the cold dome in the subcloud layer. The squall line is representative of that the part of the spectrum of mesoscale convective systems that does not have a rear inflow jet, does not produce a trailing stratiform precipitation region, and does not rely upon penetrative downdrafts to sustain the air mass within the subcloud cold dome. -from Authors