Tne partitioning of a global windfield into rotational and divergent components is unique. These components are orthogonal and imply a corresponding partitioning of the kinetic energy. For a limited domain the partitioning is neither unique nor (necessarily) orthogonal and depends on the boundary conditions. Several simple boundary conditions are examined and the resulting wind components derived. A natural partitioning into three mutually orthogonal components, the rotational, divergent and harmonic components is proposed. For a global domain the harmonic component vanishes reducing the partitioning to the usual form.