Local Energetic Constraints on Walker Circulation Strength

Wills, Robert C. J.; Levine, Xavier J.; Schneider, Tapio

doi:10.1175/jas-d-16-0219.1

Cited by 30 publications

(80 citation statements)

References 59 publications

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“…Later studies have used the moist static energy (MSE) budget to account for the canceling effects of latent heating and adiabatic cooling on circulations, relating the strength of vertical motions to the net energy input to the atmospheric column and (inversely) to a measure of the MSE stratification called the gross moist stability [51,[125][126][127][128][129]. The gross moist stability generally increases with warming due to an increase in the depth of convection [128,129], and this reduces the strength of circulations for a fixed energy input. Changes in the large-scale summer stationary wave circulation have generally been understood through consideration of the land-sea MSE contrast or horizontal temperature and MSE gradients more generally [130,131].…”

Section: Mechanisms Of Summer Changesmentioning

confidence: 99%

“…1. Weakening of vertical winds south of 40°N in both seasons due to global energetic constraints on precipitation [52,56] and an increase in gross moist stability [51,[127][128][129]; weakening of upper-tropospheric meridional winds south of 40°N in JJA that is likely coupled to the weakening of vertical winds through Sverdrup balance.…”

Section: Robust Responsesmentioning

confidence: 99%

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Northern Hemisphere Stationary Waves in a Changing Climate

Wills

White

Levine

2019

Curr Clim Change Rep

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Purpose of Review Stationary waves are planetary-scale longitudinal variations in the time-averaged atmospheric circulation. Here, we consider the projected response of Northern Hemisphere stationary waves to climate change in winter and summer. We discuss how the response varies across different metrics, identify robust responses, and review proposed mechanisms. Recent Findings Climate models project shifts in the prevailing wind patterns, with corresponding impacts on regional precipitation, temperature, and extreme events. Recent work has improved our understanding of the links between stationary waves and regional climate and identified robust stationary wave responses to climate change, which include an increased zonal lengthscale in winter, a poleward shift of the wintertime circulation over the Pacific, a weakening of monsoonal circulations, and an overall weakening of stationary wave circulations, particularly their divergent component and quasi-stationary disturbances. Summary Numerous factors influence Northern Hemisphere stationary waves, and mechanistic theories exist for only a few aspects of the stationary wave response to climate change. Idealized studies have proven useful for understanding the climate responses of particular atmospheric circulation features and should be a continued focus of future research. Keywords Stationary waves. Climate change. Rossby waves. Climate dynamics. Atmospheric general circulation This article is part of the Topical Collection on Mid-latitude Processes and Climate Change

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Section: Mechanisms Of Summer Changesmentioning

confidence: 99%

Section: Robust Responsesmentioning

confidence: 99%

Northern Hemisphere Stationary Waves in a Changing Climate

Wills

White

Levine

2019

Curr Clim Change Rep

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“…It has been used extensively in studies of tropical dynamics. [27][28][29] Considering the weak temperature and moisture gradients in the tropics and the dominance of the first baroclinic mode in vertical motion, [30][31][32] the magnitude of W u is approximately determined by the net energy flux into the atmospheric column F u net À Á divided by gross moist stability (GMS), W u = F u net /GMS. The GMS represents the efficiency of energy export out of the convective region given unit vertical ascent and is sensitive to the vertical structure of MSE and vertical motion.…”

Section: The Multi-model-meanmentioning

confidence: 99%

“…The GMS represents the efficiency of energy export out of the convective region given unit vertical ascent and is sensitive to the vertical structure of MSE and vertical motion. 31,32 In this study, we analyze the relationship between 1 Wu dWu dTs across the models, and the contributions of the GMS changes and other processes can be inferred from the residue, i.e.,…”

Section: The Multi-model-meanmentioning

confidence: 99%

A dichotomy between model responses of tropical ascent and descent to surface warming

Zhai

Jiang

et al. 2019

npj Clim Atmos Sci

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Simulations of tropical atmospheric circulation response to surface warming vary substantially across models, causing large uncertainties in projections of regional precipitation change. Understanding the physical processes that drive the model spread in tropical circulation changes is critically needed. Here we employ the basic mass balance and energetic constraints on tropical circulation to identify the dominant factors that determine multidecadal circulation strength and area changes in climate models. We show that the models produce a robust weakening of descent rate under warming regardless of surface warming patterns; however, ascent rate change exhibits inter-model spread twice as large as descent rate because of diverse model responses in the radiative effects of clouds, water vapor, and aerosols. As ascent area change is dictated by the disparate descent and ascent rate changes due to the mass budget and the inter-model spread in descent rate change is small, the model spread in ascent area change is dominated by that of ascent rate change, resulting in a strong anti-correlation of -0.85 between the fractional changes of ascent strength and area across 77 climate model simulations. This anti-correlation leads to a corresponding inverse relationship between the rates of precipitation intensifying and narrowing of the inter-tropical convergence zone (ITCZ), suggesting tropical ascent area change can be potentially used to constrain the ITCZ precipitation change. Longwave cloud radiative effect at the topof-atmosphere (TOA) in the convective region is identified to be a major source of uncertainties for tropical ascent rate change and thus for regional precipitation change.npj Climate and Atmospheric Science (2019) 2:8 ; https://doi.

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“…A number of thermodynamic mechanisms have been proposed to explain changes in tropical circulation with global warming. In particular, an increase in static stability-both dry and moist stability-has been suggested as the primary cause of the weakening of tropical circulations (Knutson and Manabe 1995;Chou and Neelin 2004;Ma et al 2012;Wills et al 2017). Dry static stability is expected to increase as the tropical troposphere shifts to a warmer moist adiabatic temperature profile, while the tropical-mean gross moist stability has been argued to increase as climate warms because of an upward shift in the tropical tropopause and the height of moist convection (Chou and Chen 2010;Chou et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of subtropical stationary circulations to global warming in climate models: a baroclinic Rossby gyre theory

Levine

Boos

2018

Clim Dyn

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Time-mean, zonally asymmetric circulations maintain an intense hydrologic contrast between monsoon regions and subtropical drylands in Earth's present climate. Climate model simulations suggest that this hydrologic contrast will increase in twenty-first-century global warming scenarios, but the response of the zonally asymmetric circulations to global mean temperature is poorly understood. Here we adapt a simple theory for the strength of time-mean, subtropical, zonally asymmetric circulations (hereafter called stationary circulations) and demonstrate its relevance to summer stationary circulation changes in the Northern Hemisphere in an ensemble of comprehensive climate model simulations of global warming. The theory, which is based on the dynamics of a subtropical Rossby gyre that is in Sverdrup balance and has the vertical structure of a first-baroclinic mode, shows that the weakening of stationary ascent with global warming in the multi-model mean can be represented as a compensation between two processes: a lifting of the tropical tropopause and a decrease of the tropospheric zonal temperature gradient, which respectively require strengthening and weakening of vertical mass flux in the Rossby gyre. A large fraction of the intermodel variance in global warming-induced changes in stationary ascent is associated with intermodel variance in zonal tropospheric temperature gradient changes, which we in turn attribute to intermodel variance in zonal sea surface temperature gradient changes. These results show that much of the sensitivity of subtropical hydrologic contrasts to global mean temperature can be understood in terms of a linear vorticity balance and properties of moist adiabats.

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Local Energetic Constraints on Walker Circulation Strength

Cited by 30 publications

References 59 publications

Northern Hemisphere Stationary Waves in a Changing Climate

Northern Hemisphere Stationary Waves in a Changing Climate

A dichotomy between model responses of tropical ascent and descent to surface warming

Sensitivity of subtropical stationary circulations to global warming in climate models: a baroclinic Rossby gyre theory

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