Upper-bound general circulation of coupled ocean–atmosphere: Part 1. Atmosphere

• Published in: Dynamics of atmospheres and oceans 2013-11, Vol.64, p.10-26
• Main Author: Ou, Hsien-Wang
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Extratropical tropopause; General atmosphere circulation; Maximum entropy production; Meridional cells; Potential vorticity mixing
• ISSN: 0377-0265; 1872-6879
• DOI: 10.1016/j.dynatmoce.2013.09.001

•Potential vorticity mixing by eddies provides the unifying dynamical principle for the general circulation of the planetary fluids.•Subjected to thermal constraint, the PV is two-banded with zero tropical value, whose inversion reproduces the prevailing wind.•The zonal wind drives the meridional cells via the Ekman dynamics, whose boundaries align with zero crossings of the zonal wind.•Hadley cell attains its prominence and seasonal asymmetry because of the singular Ekman convergence at the equator.•Extratropical tropopause is a quasi-material boundary, whose height distribution is linked to the polar front via the hydrostatic balance. We consider the general atmospheric circulation within the deductive framework of our climate theory. The preceding three parts of this theory have reduced the troposphere to the tropical and polar air masses and determined their temperature and the surface latitude of their dividing boundary, which provide the prior thermal constraint for the present dynamical derivation. Drawing upon its similar material conservation as the thermal property, the (columnar) potential vorticity (PV) is assumed homogenized as well in air masses, which moreover has a zero tropical value owing to the hemispheric symmetry. Inverting this PV field produces an upper-bound zonal wind that resembles the prevailing wind, suggesting that the latter may be explained as the maximum macroscopic motion extractable by random eddies – within the confine of the thermal differentiation. With the polar front determined in conjunction with the zonal wind, the approximate leveling of the isobars at the surface and high aloft specifies the tropopause, which is colder and higher in the tropics than in the polar region. The zonal wind drives the meridional circulation via the Ekman dynamics, and the preeminence of the Hadley cell stems from the singular Ekman convergence at the equator that allows it to supply the upward mass flux in the ITCZ demanded by the global energy balance.