Based on the theoretical and experimental facts that gravity waves (GWs) can be spontaneously emitted during the evolution of a near-balanced flow, a stochastic parameterization of GWs linked to fronts and jets is proposed. Although the spontaneous adjustment theory used predicts "exponentially" small GW fields, it is shown that it is sufficient to produce realistic GW drag at mesospheric levels. Off-line tests using reanalyzed meteorological fields are conducted and show that the GWs emitted present a strong annual cycle following that of the sources. Also, the GW momentum fluxes in the lower stratosphere are qualitatively realistic in terms of intermittency. Online tests in a middle atmosphere general circulation model show that the scheme can potentially perform as well as highly tuned existing GW schemes.