Idealized Simulations of the Intertropical Convergence Zone and Its Multilevel Flows

Nolan, David S.; Powell, Scott W.; Zhang, Chidong; Mapes, Brian E.

doi:10.1175/2010jas3417.1

Cited by 33 publications

(39 citation statements)

References 58 publications

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“…The energetic theory for ITCZ location assumes the cross-equatorial atmospheric energy flux is due entirely to the zonal-mean Hadley circulation and that energy transports by transient and stationary eddies are negligible. However, transient and stationary eddies are not generally negligible in the energy and water budgets of the tropical atmosphere in both the observed climate and in models [18,21,30,36,[111][112][113][114]. As a first step towards incorporating the influence of eddies into the energetic theory, the total cross-equatorial energy flux F 0 could be decomposed into mean (Hadley circulation), transient-eddy and stationary-eddy components (F 0 = F mean + F transient + F stationary ) and the relative influences of these processes on the climatological ITCZ and on ITCZ shifts could then be diagnosed.…”

Section: Outstanding Questionsmentioning

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

220

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: Outstanding Questionsmentioning

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

220

193

View full text Add to dashboard Cite

show abstract

“…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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“…Zhang et al (2004) used in situ observations to show the coexistence of the SMC with the northerly shallow return flow, located at 2-4 km in height, just above the boundary layer. The SMCs are found in global reanalyses (Tomas and Webster 1997;Trenberth et al 2000;Zhang et al 2008) and numerical simulations (Nolan et al 2007(Nolan et al , 2010. Nolan et al (2007) show that shallow return flows have importance in terms of the moisture transport in and out of the ITCZ, so it is meaningful to understand the behavior of the largescale circulation over the eastern Pacific in detail.…”

Section: Introductionmentioning

confidence: 99%

“…The SMCs are found in global reanalyses (Tomas and Webster 1997;Trenberth et al 2000;Zhang et al 2008) and numerical simulations (Nolan et al 2007(Nolan et al , 2010. Nolan et al (2007) show that shallow return flows have importance in terms of the moisture transport in and out of the ITCZ, so it is meaningful to understand the behavior of the largescale circulation over the eastern Pacific in detail. Note that the SMCs appear not only over the eastern Pacific but also over the central and western Pacific, Atlantic, Africa, and the Indian subcontinent (e.g., Takayabu et al 2006;Zhang et al 2006Zhang et al , 2008.…”

Section: Introductionmentioning

confidence: 99%

TRMM-Observed Shallow versus Deep Convection in the Eastern Pacific Related to Large-Scale Circulations in Reanalysis Datasets

2014

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Over the eastern Pacific, recent studies have shown that a shallow large-scale meridional circulation with its return flow just above the boundary layer coexists with a deep Hadley circulation. This study examines how the vertical structure of large-scale circulations is related to satellite-observed individual precipitation properties over the eastern Pacific in boreal autumn. Three reanalysis datasets are used to describe differences in their behavior. The results are compared among reanalyses and three distinctly different convection periods, which are defined according to their radar echo depths. Shallow and deep circulations are shown to often coexist for each of the three periods, resulting in the multicell circulation structure. Deep (shallow) circulations preferentially appear in the mostly deep (shallow) convection period of radar echo depths. Thus, depth of convection basically corresponds to which circulation branch is dominant. This anticipated relationship between the circulation structure and depths of convection is common in all three reanalyses. Notable differences among reanalyses are found in the mid-to upper troposphere in either the time-mean state or the composite analysis based on the convection periods. Reanalyses have large variations in characteristics associated with deep circulations such as the upper-tropospheric divergence and outflows and the midlevel inflows, which are consistent with their different profiles of latent heating in the mid-to upper troposphere. On the other hand, discrepancies in shallow circulations and shallow convection are also found, but they are not as large as those in deep ones.

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Idealized Simulations of the Intertropical Convergence Zone and Its Multilevel Flows

Cited by 33 publications

References 58 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

Energetic Constraints on the Width of the Intertropical Convergence Zone

TRMM-Observed Shallow versus Deep Convection in the Eastern Pacific Related to Large-Scale Circulations in Reanalysis Datasets

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