*Tellus*, **55A**, 45-60.

Adam H. Sobel

Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences,
Columbia University, New York, NY.

Christopher S. Bretherton

Department of Atmospheric Sciences, University of
Washington, Seattle, WA.

**Abstract**

The authors study the interaction of large-scale waves with deep
convection in nonrotating mesoscale model simulations, without mean
vertical shear, under idealized
boundary conditions (doubly periodic, fixed uniform sea surface
temperature). Radiative cooling is fixed, so radiative-convective
feedbacks are not considered. The model is initialized with random
thermal perturbations near the surface and then run for 16 days to a
state of approximate radiative-convective equilibrium. At this
point, a wave-like heating is imposed for one day in order to create
a wave. The heating is uniform in the meridional direction, sinusoidal with
a wavelength equal to the domain size (4500 km) in the zonal
direction, and has a roughly ``first baroclinic mode'' structure
in the vertical. After this single day of forcing, the heating
is turned off and the wave is allowed to evolve freely for seven
more days. A range of forcing phase speeds and amplitudes are used,
but two simulations are presented in detail. One has a flow-relative
forcing phase speed of 55 $ms^{-1}$ and the other of zero, and
both have maximum forcing amplitude of 10 $Kd^{-1}$. Both of
these forcings produce waves which are initially rapidly damped,
but then settle in to quasi-steadily propagating,
coherent configurations which are weakly decaying or neutral.
The authors focus on this latter period.

The faster forcing produces
a convectively coupled gravity wave qualitatively similar to those
predicted by strict quasi-equilibrium (SQE) theory, but whose interaction
with convection is weaker than that theory predicts. The adiabatic
cooling is considerably larger than the diabatic heating, and
consequently the phase speed is roughly $30 ms^{-1}$ rather than
the $10-15 ms^{-1}$ typically predicted by SQE for waves of this
vertical structure. Sensitivity studies show that this wave,
when propagating eastward against a mean westward flow, is
destabilized by linear evaporation-wind feedback. The slower forcing
produces a wave which is stationary in the mean flow frame and
does not have the structure of a gravity wave. This wave has a
much larger signal in the moisture field than does the faster wave,
and much closer cancellation between adiabatic cooling and diabatic
heating. This wave appears similar to ones appearing in some
recent theoretical studies and cloud-resolving
simulations.