Axisymmetric constraints on cross-equatorial Hadley cell extent

Abstract

We consider the relevance of known constraints from each of Hide's theorem, the angular momentum conserving (AMC) model, and the equal-area model on the extent of cross-equatorial Hadley cells. These theories respectively posit that a Hadley circulation must span: all latitudes where the radiative convective equilibrium (RCE) absolute angular momentum ($M_{\mathrm{rce}}$) satisfies $M_{\mathrm{rce}}>\Omega a^2$ or $M_{\mathrm{rce}}<0$ or where the RCE absolute vorticity (${\eta }_{\mathrm{rce}}$) satisfies $f{\eta }_{\mathrm{rce}}<0$; all latitudes where the RCE zonal wind exceeds the AMC zonal wind; and over a range such that depth-averaged potential temperature is continuous and that energy is conserved. The AMC model requires knowledge of the ascent latitude ${\phi }_{\mathrm{a}}$, which need not equal the RCE forcing maximum latitude ${\phi }_{\mathrm{m}}$. Whatever the value of ${\phi }_{\mathrm{a}}$, we demonstrate that an AMC cell must extend at least as far into the winter hemisphere as the summer hemisphere. The equal-area model predicts ${\phi }_{\mathrm{a}}$, always placing it poleward of ${\phi }_{\mathrm{m}}$. As ${\phi }_{\mathrm{m}}$ is moved poleward (at a given thermal Rossby number), the equal-area predicted Hadley circulation becomes implausibly large, while both ${\phi }_{\mathrm{m}}$ and ${\phi }_{\mathrm{a}}$ become increasingly displaced poleward of the minimal cell extent based on Hide's theorem (i.e. of supercritical forcing). In an idealized dry general circulation model, cross-equatorial Hadley cells are generated, some spanning nearly pole-to-pole. All homogenize angular momentum imperfectly, are roughly symmetric in extent about the equator, and appear in extent controlled by the span of supercritical forcing.

arXiv comment18 pages, 9 figures, published

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Cited by in corpus (5)

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• Atmospheric dynamics on terrestrial planets with eccentric orbits
• The Key Factors Controlling the Seasonality of Planetary Climate
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• Solsticial Hadley Cell ascending edge theory from supercriticality