An extended treatment of the internal energy as a thermodynamic potential in the energy-entropy picture is presented in connection with atmospheric systems under turbulent conditions. One finds that a turbulent thermodynamically autonomous energy quantity, the turbulent internal energy (TIE) which belongs to the mean state internal energy depending on averaged state variables, can be derived. The elementary relevance of TIE becomes expediently represented by means of a second-order Taylor approach; it explains TIE as the energetic response to the eddy variances of the independent thermodynamic variables of state (i.e. temperature and mass density or potential temperature). The difference of the novel concept of TIE to existing available energy formulations is discussed. ¿ 1998 American Geophysical Union