Exploring the Role of Eddy Momentum Fluxes in Determining the Characteristics of the Equinoctial Hadley Circulation: Fixed-SST Simulations

Singh, Martin S.; Kuang, Zhiming

doi:10.1175/jas-d-15-0212.1

Cited by 20 publications

(15 citation statements)

References 59 publications

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“…A more realistic control run could be obtained by prescribing additional eddy momentum (or heat) forcing in the mid-latitudes (Schneider, 1984;Singh and Kuang, 2016), as was done in Caballero and Carlson (2018). For simplicity, we prefer not to do so here.…”

Section: B Control Runmentioning

confidence: 99%

Atmospheric Bistability and Abrupt Transitions to Superrotation: Wave–Jet Resonance and Hadley Cell Feedbacks

Herbert

Caballero

Bouchet

2020

Journal of the Atmospheric Sciences

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Strong eastward jets at the equator have been observed in many planetary atmospheres and simulated in numerical models of varying complexity. However, the nature of the transition from a conventional state of the general circulation, with easterlies or weak westerlies in the tropics, to such a superrotating state remains unclear. Is it abrupt or continuous? This question may have far-reaching consequences, as it may provide a mechanism for abrupt climate change in a planetary atmosphere, both through the loss of stability of the conventional circulation and through potential noise-induced transitions in the bistability range. We study two feedbacks which may lead to bistability between a conventional and a superrotating state: the Hadley cell feedback and a wave-jet resonance feedback. We delineate the regime of applicability of these two mechanisms in a simple model of zonal acceleration budget at the equator. Then, we show using numerical simulations of the axisymmetric primitive equations that the wave-jet resonance feedback indeed leads to robust bistability, while the bistability governed by the Hadley cell feedback, although observed in our numerical simulations, is much more fragile in a multilevel model.

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Section: B Control Runmentioning

confidence: 99%

Atmospheric Bistability and Abrupt Transitions to Superrotation: Wave–Jet Resonance and Hadley Cell Feedbacks

Herbert

Caballero

Bouchet

2020

Journal of the Atmospheric Sciences

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“…On Earth, baroclinic eddies modulate the Hadley cells' extent and overturning strength (e.g. Walker and Schneider 2005;Korty and Schneider 2008;Levine and Schneider 2015;Singh and Kuang 2016;Singh et al 2017) and decelerate the zonal wind of the annual mean Hadley cells well below the AMC limit (Held and Hoskins 1985;Walker and Schneider 2006). Nevertheless, large expanses of crossequatorial, zonally confined monsoons and zonal mean Hadley cells during solsticial seasons do approximately behave as in the AMC regime, with local Rossby numbers Ro ≡ −ζ/ f ∼ 0.6 compared to Ro = 1 for the true AMC solution and Ro = 0 for the purely eddy-dominated case (e.g.…”

Section: Caveatsmentioning

confidence: 99%

Axisymmetric Constraints on Cross-Equatorial Hadley Cell Extent

Hill

Bordoni

Mitchell

2019

Journal of the Atmospheric Sciences

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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 satisfies or or where the RCE absolute vorticity satisfies ; 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 , which needs not equal the RCE forcing maximum latitude . Whatever the value of , 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 , always placing it poleward of . As is moved poleward (at a given thermal Rossby number), the equal-area-predicted Hadley circulation becomes implausibly large, while both and 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.

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“…This widening tendency is in qualitative agreement with Sobel and Neelin (2006), who found that increasing the horizontal moisture diffusivity in an axisymmetric model (analogous to increasing the transient-eddy moisture flux) resulted in a wider ITCZ. Transient eddies have previously been shown to modulate the strength of the Hadley circulation through their effect on the both the angular momentum and energy budgets (Singh and Kuang 2016) of the tropics, and are also important for the extent of the Hadley circulation (Korty and Schneider 2008;Levine and Schneider 2015). Although MSE divergence by transient eddies has been found to be an important term in the energy budgets of the eastern Pacific (Peters et al 2008) and the ITCZ in an idealized model (Nolan et al 2010), the quantitative relationship between transient eddies and the size of the ITCZ has not been demonstrated previously.…”

Section: ) Transient-eddy Component Deddymentioning

confidence: 99%

Energetic Constraints on the Width of the Intertropical Convergence Zone

Byrne

Schneider

2016

Journal of Climate

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The intertropical convergence zone (ITCZ) has been the focus of considerable research in recent years, with much of this work concerned with how the latitude of maximum tropical precipitation responds to natural climate variability and to radiative forcing. The width of the ITCZ, however, has received little attention despite its importance for regional climate and for understanding the general circulation of the atmosphere. This paper investigates the ITCZ width in simulations with an idealized general circulation model over a wide range of climates. The ITCZ, defined as the tropical region where there is time-mean ascent, displays rich behavior as the climate varies, widening with warming in cool climates, narrowing in temperate climates, and maintaining a relatively constant width in hot climates. The mass and energy budgets of the Hadley circulation are used to derive expressions for the area of the ITCZ relative to the area of the neighboring descent region, and for the sensitivity of the ITCZ area to changes in climate. The ITCZ width depends primarily on four quantities: the net energy input to the tropical atmosphere, the advection of moist static energy by the Hadley circulation, the transport of moist static energy by transient eddies, and the gross moist stability. Different processes are important for the ITCZ width in different climates, with changes in gross moist stability generally having a weak influence relative to the other processes. The results are likely to be useful for analyzing the ITCZ width in complex climate models and for understanding past and future climate change in the tropics.

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Exploring the Role of Eddy Momentum Fluxes in Determining the Characteristics of the Equinoctial Hadley Circulation: Fixed-SST Simulations

Cited by 20 publications

References 59 publications

Atmospheric Bistability and Abrupt Transitions to Superrotation: Wave–Jet Resonance and Hadley Cell Feedbacks

Atmospheric Bistability and Abrupt Transitions to Superrotation: Wave–Jet Resonance and Hadley Cell Feedbacks

Axisymmetric Constraints on Cross-Equatorial Hadley Cell Extent

Energetic Constraints on the Width of the Intertropical Convergence Zone

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