Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part I: Zonally Averaged ITCZ Position

Adam, Ori; Bischoff, Tobias; Schneider, Tapio

doi:10.1175/jcli-d-15-0512.1

Cited by 124 publications

(190 citation statements)

References 39 publications

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“…Using reanalysis data, we have recently shown that the zonal-mean EFE and ITCZ position covary on seasonal and interannual time scales and that seasonal and interannual variations of the ITCZ position can be quantitatively related to variations of the AET and its derivatives (Adam et al 2016). In the present paper, we examine the relation between the zonally varying EFE and ITCZ and extend the theoretical framework developed for zonal-mean variations Schneider 2014, 2016;Schneider et al 2014;Adam et al 2016) to regional variations.…”

Section: Introductionmentioning

confidence: 77%

“…Usually, an ITCZ and EFE north of the equator imply southward AET across the equator, away from the ITCZ, and vice versa. Indeed, the zonal-mean position of the ITCZ was found to be closely related to cross-equatorial AET in observations (e.g., Donohoe et al 2013Donohoe et al , 2014Adam et al 2016) and in climate models of varying complexity (e.g., Chiang and Bitz 2005;Broccoli et al 2006;Yoshimori and Broccoli 2008;Kang et al 2008Kang et al , 2009Donohoe et al 2013Donohoe et al , 2014.…”

Section: Introductionmentioning

confidence: 94%

“…1), where near-surface meridional mass fluxes vanish. Since the Hadley circulation transports energy away from the ITCZ and dominates the tropical energy transport, column-integrated energy fluxes also vanish and diverge near the ITCZ, forming an atmospheric energy flux equator (EFE) (e.g., Neelin and Held 1987;Broccoli et al 2006;Kang et al 2008Kang et al , 2009Donohoe et al 2013Donohoe et al , 2014Adam et al 2016).…”

Section: Introductionmentioning

confidence: 99%

“…For example, seasonal meridional migrations of marine ITCZs are small relative to their continental (monsoonal) counterparts (Fig. 1); interannual variations of the ITCZ associated with ENSO are most pronounced over the Pacific but are relatively small elsewhere (e.g., Dai and Wigley 2000;Adam et al 2016); and the eastern Pacific ITCZ bifurcates to a double ITCZ that straddles the equator during boreal spring, but such bifurcations do not usually occur elsewhere (Fig. 1, bottom;Zhang 2001;Gu et al 2005).…”

Section: Introductionmentioning

confidence: 99%

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Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part II: Zonally Varying Shifts of the ITCZ

2016

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The ITCZ lies at the ascending branch of the tropical meridional overturning circulation, where nearsurface meridional mass fluxes vanish. Near the ITCZ, column-integrated energy fluxes vanish, forming an atmospheric energy flux equator (EFE). This paper extends existing approximations relating the ITCZ position and EFE to the atmospheric energy budget by allowing for zonal variations. The resulting relations are tested using reanalysis data for 1979-2014. The zonally varying EFE is found as the latitude where the meridional component of the divergent atmospheric energy transport (AET) vanishes. A Taylor expansion of the AET around the equator relates the ITCZ position to derivatives of the AET. To a first order, the ITCZ position is proportional to the divergent AET across the equator; it is inversely proportional to the local atmospheric net energy input (NEI) that consists of the net energy fluxes at the surface, at the top of the atmosphere, and zonally across longitudes. The first-order approximation captures the seasonal migrations of the ITCZ in the African, Asian, and Atlantic sectors. In the eastern Pacific, a third-order approximation captures the bifurcation from single-to double-ITCZ states that occurs during boreal spring. In contrast to linear EFE theory, during boreal winter in the eastern Pacific, northward cross-equatorial AET goes along with an ITCZ north of the equator. EFE and ITCZ variations driven by ENSO are characterized by an equatorward (poleward) shift in the Pacific during El Niño (La Niña) episodes, which are associated with variations in equatorial ocean energy uptake.

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Section: Introductionmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part II: Zonally Varying Shifts of the ITCZ

2016

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“…[49][50][51] Thus, expanding the zonal-mean energetics framework to two horizontal dimensions is required for predictions of regional rainfall changes in the tropics, say by accounting for the zonal component of divergent AET. 46,52 The application of the energetics framework is further complicated by ocean dynamical feedback. When the ocean circulation is allowed to respond (i.e., O is no longer fixed in Eq.…”

Section: Limitations and Ways Forwardmentioning

confidence: 99%

Extratropical forcing and tropical rainfall distribution: energetics framework and ocean Ekman advection

2018

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Intense tropical rainfall occurs in a narrow belt near the equator, called the inter-tropical convergence zone (ITCZ). In the past decade, the atmospheric energy budget has been used to explain changes in the zonal-mean ITCZ position. The energetics framework provides a mechanism for extratropics-to-tropics teleconnections, which have been postulated from paleoclimate records. In atmosphere models coupled with a motionless slab ocean, the ITCZ shifts toward the warmed hemisphere in order for the Hadley circulation to transport energy toward the colder hemisphere. However, recent studies using fully coupled models show that tropical rainfall can be rather insensitive to extratropical forcing when ocean dynamics is included. Here, we explore the effect of meridional Ekman heat advection while neglecting the upwelling effect on the ITCZ response to prescribed extratropical thermal forcing. The tropical component of Ekman advection is a negative feedback that partially compensates the prescribed forcing, whereas the extratropical component is a positive feedback that amplifies the prescribed forcing. Overall, the tropical negative feedback dominates over the extratropical positive feedback. Thus, including Ekman advection reduces the need for atmospheric energy transport, dampening the ITCZ response. We propose to build a hierarchy of ocean models to systematically explore the full dynamical response of the coupled climate system.

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Relation of the double‐ITCZ bias to the atmospheric energy budget in climate models

Adam

Schneider

Brient

et al. 2016

Geophysical Research Letters

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We examine how tropical zonal mean precipitation biases in current climate models relate to the atmospheric energy budget. Both hemispherically symmetric and antisymmetric tropical precipitation biases contribute to the well‐known double‐Intertropical Convergence Zone (ITCZ) bias; however, they have distinct signatures in the energy budget. Hemispherically symmetric biases in tropical precipitation are proportional to biases in the equatorial net energy input; hemispherically antisymmetric biases are proportional to the atmospheric energy transport across the equator. Both relations can be understood within the framework of recently developed theories. Atmospheric net energy input biases in the deep tropics shape both the symmetric and antisymmetric components of the double‐ITCZ bias. Potential causes of these energetic biases and their variation across climate models are discussed.

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Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part I: Zonally Averaged ITCZ Position

Cited by 124 publications

References 39 publications

Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part II: Zonally Varying Shifts of the ITCZ

Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part II: Zonally Varying Shifts of the ITCZ

Extratropical forcing and tropical rainfall distribution: energetics framework and ocean Ekman advection

Relation of the double‐ITCZ bias to the atmospheric energy budget in climate models

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