Prescribed Heating of a Stratified Atmosphere as a Model for Moist Convection

Abstract

The response of a stratified atmosphere to a steady, moving source of heat is explored as a tool for understanding organized, moist convection. The results are shown to depend strongly on the ratio of the vertical wavelength of the forced gravity waves to the depth of the disturbance. The wave-CISK mechanism is understood as a coincidence between heating and low-level upward motion that only occurs for certain values of this ratio. Wave-CISK is shown to require precipitation-induced cooling to work satisfactorily. The cooling suppresses the subsidence wave produced by latent heat release, and allows parcels from near the surface to rise to the level of free convection. Squall lines often have a midlevel jet flowing through them from front to rear. Such a jet is seen in our simulations, and is the result of the oscillatory response of a stratified fluid to a moving beat source. The jet is strongest when evaporative cooling is included.