Linear Stratospheric Gravity Waves above Convective Thermal Forcing

Abstract

The spectra of linear gravity waves generated by a time-varying tropospheric thermal forcing representing organized convection are compared to the spectra of stratospheric gravity waves generated by organized convection in a fully nonlinear two-dimensional squall line simulation. The resemblance between the spectra in the two simulations suggests that stratospheric gravity waves above convection can be understood primarily in terms of the linear response to a time- and space-dependent thermal forcing. In particular, the linear response to thermal forcing accounts for the correlation between the dominant vertical wavelength of the stratospheric waves and the depth of the tropospheric convection as well as the the fact that the dominant frequency of the stratospheric waves is the same as the frequency of oscillation of the main convective updraft.