Abstract
Mass and Dempsey (1985) have reformulated the equations for the one-level sigma-system model over complex terrain and suggested they have removed the large hydrostatic part of the horizontal pressure-gradient force (PGF). It is shown that although the coefficient of g∇σZs was greatly reduced (compared to 1), the complete elimination of the hydrostatic PGF cannot be done unless the surface temperature is redefined as the sum of a perturbation temperature and a basic rest-state temperature. The alternative formula in which the hydrostatic PGF terms were totally removed is presented.
