Nonlinear atmospheric adjustment to momentum forcing

A nonlinear, numerical model of a compressible atmosphere is used to simulate the hydrostatic and geostrophic adjustment to a localized prescribed injection of momentum applied over five minutes with a size characteristic of an isolated, deep, cumulus cloud. A variety of momentum forcings are examined including vertical, horizontally divergent, and horizontally non-divergent forcings as well as that of transverse circulations satisfying the anelastic continuity equation. The adjustments in three model atmospheres (an isothermal, a constant lapse rate, and one with a stratosphere) are studied. This theoretical study is relevant to the initialization of updrafts in compressible numerical weather prediction models. The vertical momentum forcing generates acoustic and buoyancy waves. In the non-isothermal atmosphere, the forcing also excites Lamb waves. The energetics are examined using traditional and Eulerian available energetics. Traditional energetics consists of kinetic, internal, and potential energies. The traditional energy perturbation oscillates between the potential and the internal energies with a period of 44 seconds. This oscillation is associated with the propagation of vertically trapped acoustic waves. Eulerian available energetics consists of kinetic, available potential, and available elastic energies. The forcing results in the addition of kinetic energy that is then converted to available potential and elastic energies. The amplitudes of the kinetic and available potential energies are similar after the forcing has ended with an order of magnitude weaker available elastic component. Research on forcings other than vertical momentum is in progress and results for them will be presented at the conference.