The Temporal Behavior of Numerically Simulated Multicell-Type Storms. Part II: The Convective Cell Life Cycle and Cell Regeneration

Abstract

The authors study herein the convective cell life cycle and the cell generation process in mature, multicellular squall-line storms possessing well-developed subcloud cold pools using two- and three-dimensional models. The multicellular storm establishes new cells on its forward side, in the vicinity of the forced updraft formed at the pool boundary, that first intensify and then decay as they travel rearward within the storm?s upward sloping front-to-rear airflow. The principal effort is expended on the two-dimensional case owing to the strong similarity in basic behavior seen in the two geometries. The cell life cycle is examined in several complementary fashions. The cells are shown to be convectively active entities that induce local circulations that alternately enhance and suppress the forced updraft, modulating the influx of the potentially warm inflow. This transient circulation also drives the episodic mixing of stable air into the inflow that results in the cell?s ultimate dissipation. The timing of cell regeneration is also examined; an explanation involving two separate and successive phases, each with their own timescales, is proposed. The second of these phases can be shortened if a ?convective trigger,? another by-product of the cell?s circulation, is present in the storm?s inflow environment. Sensitivity of the results to strictly numerical model details is also discussed.