A Further Study of the Mechanisms of Cell Regeneration, Propagation, and Development within Two-Dimensional Multicell Storms

Abstract

The mechanisms of cell regeneration, development, and propagation within a two-dimensional multicell storm proposed by Lin, Deal, and Kulie (hereafter LDK) were further investigated by conducting a series of sensitivity tests. LDK's advection mechanism was reexamined by performing simulations utilizing a plateau with five additional wind profiles having a wider range of shear. All five cases gave results that show that the cell regeneration period decreases with the storm-relative midlevel inflow, similar to that proposed by LDK. It was also found that a rigid lid is not an appropriate upper boundary condition for multicell storm simulations. In order to test whether the advection mechanism is responsible for cell regeneration with a different sounding, an idealized sounding was used. A multicell storm was produced along with a strong density current and gust front updraft. Investigation of this storm supports the advection mechanism within the growing mode and a gravity wave mechanism in the propagation mode, as proposed by LDK. From further investigation, the relaxation mechanism proposed by Fovell and Tan was shown to exist within these simulations yet found to be dependent on the advection mechanism to cause cell regeneration. To avoid some problems that occurred when using a plateau, a prescribed heat sink was used to produce a more realistic density current. This experiment demonstrates that the advection mechanism is responsible for cell regeneration and the gravity wave mechanism is responsible for cell propagation within the storm. It was found that without precipitation loading, an individual cell is still able to split. In this case, the compensating downdraft produced by vertical differential advection is responsible for cell splitting and merging.