The response of an unbounded and isothermal atmosphere to a point impulse of force is studied. Fronts of disturbances propagate with two different speeds corresponding to acoustic waves and gravity waves. The distributions of kinetic-energy density in the two wakes behind the two fronts are calculated. A striking result is that, behind the acoustic front, the radiation density is very intense above and below the source, if the atmosphere is sufficiently stable to convection. This result may be of interest in connection with the formation of spicule structures in the solar upper chromosphere.