DYNAMICAL ADJUSTMENT OF THE TRADE-WIND INVERSION LAYER

In schematic north-south cross sections the trade inversion layer is often depicted as sloping upward as air flows toward the intertropical convergence zone. This conceptual view is consistent with purely thermodynamic boundary-layer models, which predict a deeper boundary layer with increasing sea surface temperature and decreasing large-scale subsidence. The slopes implied by such thermodynamic models and incorporated into schematic diagrams are approximately 2000 m/1000 km. In contrast, observational studies of the inversion structure over the Atlantic and Pacific Oceans reveal a less dramatic slope, on the order of 300 m/1000 km. To address this inconsistency, the authors adopt a somewhat different view of the trade inversion layer. In particular, rather than regarding it as a purely thermodynamic structure, it is regarded as a dynamical structure. By formulating a generalization of the Rossby adjustment problem, the authors investigate the dynamical adjustments of a trade wind inversion layer of variable strength and depth. From the solution of the adjustment problem, there emerges the notion that the subtropics control the inversion structure in the Tropics; that is, the subtropical inversion height is dynamically extended into the Tropics in such a way that there is little variation in the depth of the boundary layer.