SYMMETRICAL FLOW OF A MODIFIED HADLEY-CELL MODEL WITH A FREE-SURFACE

Numerical studies are conducted of symmetric flows in an infinite hori zontal fluid layer with a constant horizontal temperature gradient. A modified rotating Hadley-cell flow configuration is devised by adoptin g the free-slip and thermally insulated upper boundary. For this model , an analytic solution is available as the basic slate. A finite volum e numerical procedure is utilized to integrate the fully nonlinear Nav ier-Stokes equations over broad parameter ranges of the thermal Rossby number, Ro, and the Richardson number, Ri. The Ro-Ri diagram illustra tes several flow regimes. In the present framework, both the symmetric instability and Benard-type convective instability are found to occur . These are associated respectively with a negative potential vorticit y in the interior and a gravitationally unstable vertical temperature gradient in the thermal boundary layer. The detailed flow structures a re computed to reveal the characteristic features of these two instabi lities. Time dependent responses are analyzed to examine the dominant mechanism for two-dimensional flow developments. The interaction of th e symmetric flows with the basic-state flow field is scrutinized.