Toward an analytical, predictive theory for the location of Hadley and monsoonal cell ascending branches
Abstract
A closed, predictive theory for the location of the ascending branches of monsoonal cells and the Hadley cells --- or, nearly equivalently, the ITCZ location --- has been long sought. In the past decade, focus has been primarily on the ITCZ shifts framework, but this is ultimately diagnostic and fails in many contexts. Here we revisit instead arguments stemming from classical axisymmetric theory originally derived in the 1980s and 1990s, in particular Hide's Theorem. We clarify the central result from Hide's Theorem that the radiative-convective equilibrium absolute vorticity zero crossing signifies a lower bound on the overturning circulation extent in the summer hemisphere absent significant eddy stresses. We present evidence that this lower bound is also useful as an actual predictor, i.e. that in several contexts (including for Earth's real-world cells throughout the annual cycle) the actual ascent branch location is not removed far poleward therefrom, or at least that the separation scales in a simple way. In contrast, two arguably better-known metrics --- the "equal-area" model prediction and the Prive and Plumb diagnostic --- incorrectly predict ascent near the summer pole under solsticial forcing. We discuss the connections to Singh's recent diagnostic based on convective slantwise neutrality, in particular the distinction between true angular momentum conservation across an overturning cell and angular momentum conservation along overturning cell streamlines. Time permitting, we also discuss other implications of these results.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A23F..01H
- Keywords:
-
- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3319 General circulation;
- ATMOSPHERIC PROCESSES;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 3373 Tropical dynamics;
- ATMOSPHERIC PROCESSES