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

Adam, Ori; Bischoff, Tobias; Schneider, Tapio

doi:10.1175/jcli-d-15-0710.1

Cited by 79 publications

(115 citation statements)

References 34 publications

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“…An energetic theory has been developed over the past two decades to diagnose how processes in Earth's climate-including radiation asymmetries between hemispheres, atmosphere-ocean coupling, and energy input to the tropical atmosphere-control the zonal-mean ITCZ location [10][11][12][13][14][15][16][17][18][19][20][21]. This theory has recently been extended to understand variations of the ITCZ location with longitude [22,23]. Four recent review articles have comprehensively synthesized this body of research on the ITCZ location [1,[24][25][26].…”

Section: Earth's Deep-tropical Climate Is Dominated By the Intertropimentioning

confidence: 99%

Response of the Intertropical Convergence Zone to Climate Change: Location, Width, and Strength

Byrne¹,

Pendergrass²,

Rapp³

et al. 2018

Curr Clim Change Rep

209

193

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Purpose of Review The intertropical convergence zone (ITCZ) is a planetary-scale band of heavy precipitation close to the equator. Here, we consider the response of the ITCZ structure to climate change using observations, simulations, and theory. We focus on the substantial yet underappreciated projected changes in ITCZ width and strength, and highlight an emerging conceptual framework for understanding these changes. Recent FindingsSatellite observations and reanalysis data show a narrowing and strengthening of precipitation in the ITCZ over recent decades in both the Atlantic and Pacific basins, but little change in ITCZ location. Consistent with observations, coupled climate models predict no robust change in the zonal-mean ITCZ location over the twenty-first century. However, the majority of models project a narrowing of the ITCZ and weakening mean ascent. Interestingly, changes in ITCZ width and strength are strongly anti-correlated across models.Summary The ITCZ has narrowed over recent decades yet its location has remained approximately constant. Climate models project further narrowing and a weakening of the average ascent within the ITCZ as the climate continues to warm. Following intense work over the last ten years, the physical mechanisms controlling the ITCZ location are now well understood. The development of complementary theories for ITCZ width and strength is a current research priority. Outstanding challenges include understanding the ITCZ response to past climate changes and over land versus ocean regions, and better constraining all aspects of the ITCZ structure in model projections.

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Section: Earth's Deep-tropical Climate Is Dominated By the Intertropimentioning

confidence: 99%

Response of the Intertropical Convergence Zone to Climate Change: Location, Width, and Strength

Byrne¹,

Pendergrass²,

Rapp³

et al. 2018

Curr Clim Change Rep

209

193

View full text Add to dashboard Cite

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“…Variants of the bifurcated ITCZ pattern exist in the present tropical climate on time scales of days or longer: daily states of the ITCZ in the eastern Pacific vary between single and double ITCZs that straddle the equator (Haffke et al, ), with increased occurrence of double‐ITCZ states during boreal spring and during La Niña episodes (Adam et al, ; Bischoff & Schneider, ; Gu et al, ; Zhang, ); infrequent seasonal occurrences of double‐ITCZ states are observed over the Indian Ocean and central Pacific (e.g., Zhang, ); a regional bifurcation from a single ITCZ in the Indian Ocean to a south Pacific convergence zone (SPCZ) and a Pacific ITCZ north of the equator is observed year round (e.g., Adam et al, ). Additionally, modern climate models tend to have more pronounced double ITCZs in the Pacific than is observed (e.g., Lin, ).…”

Section: Introductionmentioning

confidence: 99%

“…Regions hosting a single ITCZ are characterized by monsoonal circulations, which are Hadley‐like in the zonal mean (e.g., Dima & Wallace, ). On the other hand, regions hosting double ITCZs that straddle the equator are associated with non‐Hadley‐like meridional overturning circulations: the double ITCZs lie along the rising branches of narrow meridional overturning circulations on either side of the equator, with a shared equatorial descending branch (Adam et al, ; Bischoff & Schneider, ). The bifurcation from single to double ITCZs is therefore linked to a bifurcation of the tropical overturning circulation (Bischoff & Schneider, ).…”

Section: Introductionmentioning

confidence: 99%

Zonally Varying ITCZs in a Matsuno‐Gill‐Type Model With an Idealized Bjerknes Feedback

Adam¹

2018

J Adv Model Earth Syst

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In the present climate, tropical rain bands exhibit a bifurcated pattern, continuously forming along single intertropical convergence zones (ITCZs) in some regions, and along double ITCZs that straddle the equator in other regions. This bifurcated ITCZ pattern is studied in a Matsuno-Gill-type model forced by relaxation to zonally asymmetric surface pressure. The model includes an idealized Bjerknes feedback which couples surface winds and sea surface temperatures (SSTs) via oceanic Ekman balance. Consistent with observations, solutions in the limit of strong damping are explored. Two ITCZ bifurcation mechanisms are identified. First, in the viscous limit, ITCZs form along negative anomalies of the local Rossby number, which tend to occur near the equator for equatorial low pressure and off the equator for equatorial high pressure; this leads to a single ITCZ in the rising branch of zonal-overturning circulations and a double ITCZ that straddles the equator in the descending branch. Second, ocean upwelling produces an equatorial cold tongue with increased surface pressure, which reduces vertical winds and can lead to precipitation peaks that straddle the equator in regions of near-equator ascent. Consistent with observations, the cold tongue intensifies with increasing zonal SST gradients, and its base widens with weakened poleward SST gradients, modulating the zonal orientation of the ITCZs on either side of the cold tongue. Analytic approximate solutions in the viscous limit capture the emergence of the bifurcated ITCZ pattern, as well as the dependence of the bifurcated ITCZ pattern on zonal and poleward SST gradients Plain Language Summary Tropical rain bands lie along near-surface convergence zones where the lower branches of the meridional overturning circulation intersect. In the present climate, tropical rain bands exhibit a bifurcated pattern, continuously forming along single intertropical convergence zones (ITCZs) in some regions, and along double ITCZs that straddle the equator in other regions. Since the tropical overturning circulations in regions dominated by single and double ITCZs are inextricably linked, a theory of the zonally varying tropical rain belt requires consideration of the bifurcated ITCZ pattern (i.e., concurrent single and double ITCZs) as a whole. In this paper, a classical simple model of the tropical circulation is used to gain a conceptual understanding of the bifurcated ITCZ pattern. It is found that the bifurcated ITCZ pattern emerges in the limit of strong mechanical damping. In addition, when surface winds are coupled to ocean heat transport, an equatorial cold tongue emerges which modulates the intensity and regional characteristics of the bifurcated ITCZ pattern in a manner consistent with observations.

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“…On a regional scale, Stanfield et al () used several metrics to characterize the North Pacific ITCZ, such as its width, its centerline position, and its magnitude. A number of studies have evaluated the influence of different drivers on the position of the ITCZ (e.g., Adam et al, , ; Bischoff & Schneider, , ; Harrop & Hartmann, ; Kang et al, ; Möbis & Stevens, ; Philander et al, ; Popp & Silvers, ; Vellinga & Wood, ) and the width of the ITCZ (Byrne & Schneider, ); however, the absence of a suitable terminology for describing the tropical zonal‐mean precipitation has led to a lack of clarity.…”

Section: Introductionmentioning

confidence: 99%

Quantifying the Zonal‐Mean Structure of Tropical Precipitation

Popp

Lutsko

2017

Geophysical Research Letters

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The tropical zonal‐mean precipitation in climate models is well known to have substantial biases such as an erroneous double intertropical convergence zone in the Pacific, but a comprehensive quantification of these biases is currently missing. Therefore, we introduce a set of nine indicators that fully characterize the position and magnitude of the tropical extrema in zonal‐mean precipitation. An analysis of the Coupled Model Intercomparison Project (CMIP) historical and Atmospheric Model Intercomparison Project (AMIP) simulations reveals large biases in the position and, especially, in the magnitude of the zonal‐mean precipitation extrema in both sets of simulations relative to observations. We find some of the nine indicators to be correlated, and that the structure of tropical precipitation can be well represented using four indicators, though these indicators are different in AMIP and CMIP. Previously defined indicators can only partly explain the biases, and so the more comprehensive terminology introduced here is a useful tool for characterizing tropical precipitation.

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

Cited by 79 publications

References 34 publications

Response of the Intertropical Convergence Zone to Climate Change: Location, Width, and Strength

Response of the Intertropical Convergence Zone to Climate Change: Location, Width, and Strength

Zonally Varying ITCZs in a Matsuno‐Gill‐Type Model With an Idealized Bjerknes Feedback

Quantifying the Zonal‐Mean Structure of Tropical Precipitation

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