  The excitation of internal gravity waves by penetrative convective plumes is
investigated using 2-D direct simulations of compressible convection. The wave
generation is quantitatively studied from the linear response of the radiative
zone to the plumes penetration, using projections onto the g-modes solutions of
the associated linear eigenvalue problem for the perturbations. This allows an
accurate determination of both the spectrum and amplitudes of the
stochastically excited modes. Using time-frequency diagrams of the mode
amplitudes, we then show that the lifetime of a mode is around twice its period
and that during times of significant excitation up to 40% of the total kinetic
energy may be contained into g-modes.
