Meridional thermal field of a coupled ocean-atmosphere system: a conceptual model

Abstract

This paper constitutes the author’s continuing effort in the construction of a minimal theory of the earth’s climate. In an earlier paper published in the Journal of Climate in 2001, this author has derived the global-mean fields of an aquatic planet forced by the solar insolation, which provide the necessary constraints for the present derivation of the meridional thermal field. The model closure invokes maximized entropy production (MEP), a thermodynamic principle widely used in turbulence and climate studies.

Based on differing convective regimes of the ocean and atmosphere, both fluids are first reduced two thermal masses with aligned fronts, consistent with a minimal description of the observed field. Subjected to natural bounds, a robust solution is then found, characterized by an ice-free ocean, near-freezing cold fluid masses, mid-latitude fronts, and comparable ocean and atmosphere heat transports. The presence of polar continents, however, sharply reduces the ocean heat transport outside the tropics, but leaves the thermal field largely unchanged.

Given the limitation of an extremely crude model, the deduced thermal field nonetheless seems sensible, suggesting that the model has captured the physics for a minimal account of the observed field. Together with the above-mentioned paper, the model reinforces the pre-eminent role of the triple point of water in stabilizing the surface temperature – against changing external condition. Such internal control is made possible by the turbulent nature of the climate fluids, which necessitates a selection rule based on extremization.