The generation and propagation of a nocturnal squall line. Part II: numerical simulations

Abstract

The mechanisms described in Part I are examined with a numerical cloud model. The first numerical experiments begin with a horizontally uniform environment. A primary squall line is generated in this environment and is then allowed to decay. Four hours after the decay, a second convective system develops at the leading edge of the gust front from the primary squall line. It is shown that this secondary generation is due to a mesoscale oscillation centered at 70 kPa that is forced by the previous convective system. Horizontal variations in the upstream environment are then considered. An increase in low-level moisture is examined first, and it is shown that the consequent lowering of the level of free convection (LFC) allows the gust front to trigger new convection. Horizontal increases in low-level shear are then considered. In the region of enhanced shear, the lifting at the gust front is increased and consequently new convection can be triggered. -from Authors