Mid-latitude interactions expand the Hadley circulation

TL;DR

This paper extends the classical Hadley circulation model to include mid-latitude interactions, revealing that changes in poleward heat flux influence the expansion or contraction of the Hadley cell, with implications for climate change.

Contribution

It introduces a modified theoretical model of the Hadley circulation that accounts for mid-latitude heat flux interactions, enhancing understanding of its variability.

Findings

Increased poleward heat flux strengthens the Hadley cell.

Decreased heat flux weakens the Hadley cell.

Global warming may cause poleward expansion of the Hadley cell.

Abstract

The Hadley circulation describes a planetary-scale tropical atmospheric flow, which has a major influence on climate. Contemporary theoretical understanding is based upon angular momentum conservation, the basic dynamical constraint governing the state of the flow pattern. However, despite the degree of success in representing the Hadley circulation, the canonical theoretical model does not treat interactions with other regions, particularly the mid-latitudes. Here, we extend the original model of Held and Hou (1980) to include the influence of mid-latitude large-scale atmospheric dynamics, which we treat using the planetary-scale heat equation with a parameterized poleward heat flux driven by synoptic eddies. The energy flux balance within the Hadley cell includes the poleward heat flux at the poleward edge of the cell, which is controlled by the baroclinic instability of the sub-tropical jet. We find that an increase (decrease) in the poleward heat flux leads to a strengthening (weakening) tropical convection, driving an equatorward (poleward) shift of the edge of the Hadley cell. Thus, our theoretical solutions suggest that global warming, which can reduce the baroclinicity of the subtropical jet, can lead to the poleward expansion of the Hadley cell due to the change in energy flux balance within it.