Dynamical Adjustment of the Trade Wind Inversion Layer

Wayne H. Schubert Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

Search for other papers by Wayne H. Schubert in
Current site
Google Scholar
PubMed
Close
,
Paul E. Ciesielski Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

Search for other papers by Paul E. Ciesielski in
Current site
Google Scholar
PubMed
Close
,
Chungu Lu Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

Search for other papers by Chungu Lu in
Current site
Google Scholar
PubMed
Close
, and
Richard H. Johnson Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

Search for other papers by Richard H. Johnson in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

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.

Abstract

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.

Save