Response of the Zonal Mean Atmospheric Circulation to El Niño versus Global Warming

Abstract The change in the zonal mean atmospheric circulation under global warming is studied in comparison with the response to El Niño forcing, by examining the model simulations conducted for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. In contrast to the strengthening and contraction of the Hadley cell and the equatorward shift of the tropospheric zonal jets in response to El Niño, the Hadley cell weakens and expands poleward, and the jets move poleward in a warmed climate, despite the projected “El Niño–like” enhanced warming over the equatorial central and eastern Pacific. The hydrological impacts of global warming also exhibit distinct patterns over the subtropics and midlatitudes in comparison to the El Niño. Two feasible mechanisms are proposed for the zonal mean circulation response to global warming: 1) The increase in static stability of the subtropical and midlatitude troposphere, a robust result of the quasi-moist adiabatic adjustment to the surface warming, may stabilize the baroclinic eddy growth on the equatorward side of the storm tracks and push the eddy activity and the associated eddy-driven wind and subsidence poleward, leading to the poleward expansion of the Hadley cell and the shift of midlatitude jets; 2) the strengthening of the midlatitude wind at the upper troposphere and lower stratosphere, arguably a consequence of increases in the meridional temperature gradient near the tropopause level due to the tropospheric warming and tropopause slope, may increase the eastward propagation of the eddies emanating from the midlatitudes, and thus the subtropical region of wave breaking displaces poleward together with the eddy-driven circulation. Both mechanisms are somewhat, if not completely, distinct from those in response to the El Niño condition.

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Weakened Impact of the Developing El Niño on Tropical Indian Ocean Climate Variability under Global Warming

Journal of Climate ◽

10.1175/jcli-d-19-0165.1 ◽

2019 ◽

Vol 32 (21) ◽

pp. 7265-7279 ◽

Cited By ~ 2

Author(s):

Chao He ◽

Yuhao Wang ◽

Tim Li

Keyword(s):

Global Warming ◽

Indian Ocean ◽

Atmospheric Circulation ◽

El Niño ◽

El Nino ◽

Tropical Indian Ocean ◽

Static Stability ◽

Circulation Anomaly ◽

Sst Anomaly ◽

Atmospheric Circulation Anomaly

Abstract El Niño induces an anomalous easterly wind along the equator and a pair of anomalous anticyclones straddling the equator over the tropical Indian Ocean (TIO) during the autumn of its developing phase. Based on 30 coupled models participating in CMIP5, these atmospheric circulation anomalies over TIO are substantially weakened by about 12%–13% K−1 under global warming scenarios, associated with a weakened zonal gradient of the sea surface temperature (SST) anomaly. The mechanism for the response is investigated based on a hierarchy of model experiments. Based on stand-alone atmospheric model experiments under uniform and patterned mean-state SST warming, the atmospheric circulation anomaly over TIO during the autumn of the developing El Niño is also substantially weakened by about 8% K−1 even if the interannual variability of SST remains exactly unchanged, suggesting that the primary cause resides in the atmosphere rather than the SST anomaly. The tropospheric static stability is robustly enhanced under global warming, and experiments performed by a linear baroclinic model show that a much weaker atmospheric circulation anomaly over TIO is stimulated by an unchanged diabatic heating anomaly under a more stable atmosphere. The weakened atmospheric circulation anomaly due to enhanced static stability weakens the zonal gradient of the SST anomaly within TIO through local air–sea interaction, and it acts to further weaken the atmospheric circulation anomaly. The enhanced static stability of the troposphere is probably the primary cause and the air–sea interaction within TIO is a secondary cause for the weakened impact of the developing El Niño on atmospheric circulation variability over TIO.

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Sensitivities and Mechanisms of the Zonal Mean Atmospheric Circulation Response to Tropical Warming

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-0298.1 ◽

2013 ◽

Vol 70 (8) ◽

pp. 2487-2504 ◽

Cited By ~ 35

Author(s):

Lantao Sun ◽

Gang Chen ◽

Jian Lu

Keyword(s):

Global Warming ◽

El Niño ◽

El Nino ◽

Atmospheric Model ◽

Hadley Cell ◽

Upper Troposphere ◽

Future Global Warming ◽

Large Ensembles ◽

Poleward Shift ◽

Mean Circulation

Abstract Although El Niño and global warming are both characterized by warming in the tropical upper troposphere, the latitudinal changes of the Hadley cell edge and midlatitude eddy-driven jet are opposite in sign. Using an idealized dry atmospheric model, the zonal mean circulation changes are investigated with respect to different patterns of tropical warming. Generally speaking, an equatorward shift in circulation takes place in the presence of enhanced tropical temperature gradient or narrow tropical warming, similar to the changes associated with El Niño events. In contrast, the zonal mean atmospheric circulations expand or shift poleward in response to upper-tropospheric warming or broad tropical warming, resembling the changes under future global warming. The mechanisms underlying these opposite changes in circulation are investigated by comparing the dry dynamical responses to a narrow tropical warming and a broad warming as analogs for El Niño and global warming. When running the idealized model in a zonally symmetric configuration in which the eddy feedback is disabled, both the narrow and broad warmings give rise to an equatorward shift of the subtropical jet. The eddy adjustment is further examined using large ensembles of transient response to a sudden switch-on of the forcing. For both narrow and broad tropical warmings, the jets move equatorward initially. In the subsequent adjustment, the initial equatorward shift is further enhanced and sustained by the low-level baroclinicity under the narrow tropical warming, whereas the initial equatorward shift transitions to a poleward shift associated with altered irreversible mixing of potential vorticity in the upper troposphere in the case of broad warming.

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Tropical SST Response to Global Warming in the Twentieth Century

Journal of Climate ◽

10.1175/2008jcli2164.1 ◽

2009 ◽

Vol 22 (5) ◽

pp. 1305-1312 ◽

Cited By ~ 4

Author(s):

Xiaojie Zhu ◽

Zhengyu Liu

Keyword(s):

Twentieth Century ◽

Global Warming ◽

El Niño ◽

El Nino ◽

Heat Fluxes ◽

Intergovernmental Panel ◽

Clear Trend ◽

Model Simulations ◽

Warming Scenario ◽

Global Warming Scenario

Abstract The trend of sea surface temperature (SST) in the twentieth century is examined in observations and the Intergovernmental Panel on Climate Change (IPCC) twentieth-century simulations. The observed SST neither shows a clear signal of the enhanced equatorial response (EER) warming nor exhibits a clear trend of the El Niño–like warming in the last century. Similarly, the IPCC simulations show neither a clear EER warming nor an El Niño–like warming in the last century. Furthermore, the comparison of heat fluxes in model simulations of the global warming scenario and the twentieth century indicates that the aerosol cooling effect, opposite to the greenhouse gases warming effect, plays an important role in the twentieth century and explains the EER-like signal in the twentieth-century simulations. Therefore, a conclusion that the IPCC model simulations of the twentieth century are consistent with observations within the error bars as well as the future projection of the EER warming pattern in the global warming scenario are validated.

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Understanding Hadley Cell Expansion versus Contraction: Insights from Simplified Models and Implications for Recent Observations

Journal of Climate ◽

10.1175/jcli-d-12-00598.1 ◽

2013 ◽

Vol 26 (12) ◽

pp. 4304-4321 ◽

Cited By ~ 61

Author(s):

Neil F. Tandon ◽

Edwin P. Gerber ◽

Adam H. Sobel ◽

Lorenzo M. Polvani

Keyword(s):

Global Warming ◽

El Niño ◽

General Circulation ◽

El Nino ◽

Circulation Model ◽

Hadley Cell ◽

Thermal Forcing ◽

Narrow Region ◽

Definition Of ◽

The Tropics

Abstract This study seeks a deeper understanding of the causes of Hadley Cell (HC) expansion, as projected under global warming, and HC contraction, as observed under El Niño. Using an idealized general circulation model, the authors show that a thermal forcing applied to a narrow region around the equator produces “El Niño–like” HC contraction, while a forcing with wider meridional extent produces “global warming–like” HC expansion. These circulation responses are sensitive primarily to the thermal forcing’s meridional structure and are less sensitive to its vertical structure. If the thermal forcing is confined to the midlatitudes, the amount of HC expansion is more than three times that of a forcing of comparable amplitude that is spread over the tropics. This finding may be relevant to recently observed trends of rapid tropical widening. The shift of the HC edge is explained using a very simple model in which the transformed Eulerian mean (TEM) circulation acts to diffuse heat meridionally. In this context, the HC edge is defined as the downward maximum of residual vertical velocity in the upper troposphere ; this corresponds well with the conventional Eulerian definition of the HC edge. In response to a positive thermal forcing, there is anomalous diabatic cooling, and hence anomalous TEM descent, on the poleward flank of the thermal forcing. This causes the HC edge () to shift toward the descending anomaly, so that a narrow forcing causes HC contraction and a wide forcing causes HC expansion.

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Intermodel Uncertainty in ENSO Amplitude Change Tied to Pacific Ocean Warming Pattern

Journal of Climate ◽

10.1175/jcli-d-16-0039.1 ◽

2016 ◽

Vol 29 (20) ◽

pp. 7265-7279 ◽

Cited By ~ 44

Author(s):

Xiao-Tong Zheng ◽

Shang-Ping Xie ◽

Liang-Hong Lv ◽

Zhen-Qiang Zhou

Keyword(s):

Global Warming ◽

El Niño ◽

El Nino ◽

Southern Oscillation ◽

Rainfall Variability ◽

Ocean Warming ◽

Amplitude Change ◽

Surface Warming ◽

Warming Pattern ◽

Projected Change

Abstract How El Niño–Southern Oscillation (ENSO) will change under global warming affects changes in extreme events around the world. The change of ENSO amplitude is investigated based on the historical simulations and representative concentration pathway (RCP) 8.5 experiments in phase 5 of the Coupled Model Intercomparison Project (CMIP5). The projected change in ENSO amplitude is highly uncertain with large intermodel uncertainty. By using the relative sea surface temperature (SST) as a measure of convective instability, this study finds that the spatial pattern of tropical Pacific surface warming is the major source of intermodel uncertainty in ENSO amplitude change. In models with an enhanced mean warming in the eastern equatorial Pacific, the barrier to deep convection is reduced, and the intensified rainfall anomalies of ENSO amplify the wind response and hence SST variability. In models with a reduced eastern Pacific warming, conversely, ENSO amplitude decreases. Corroborating the mean SST pattern effect, intermodel uncertainty in changes of ENSO-induced rainfall variability decreases substantially in atmospheric simulations forced by a common ocean warming pattern. Thus, reducing the uncertainty in the Pacific surface warming pattern helps improve the reliability of ENSO projections. To the extent that correcting model biases favors an El Niño–like mean warming pattern, this study suggests an increase in ENSO-related SST variance likely under global warming.

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Addendum: Butterfly effect and a self-modulating El Niño response to global warming

Nature ◽

10.1038/s41586-021-03261-4 ◽

2021 ◽

Vol 591 (7849) ◽

pp. E14-E15

Author(s):

Wenju Cai ◽

Benjamin Ng ◽

Tao Geng ◽

Lixin Wu ◽

Agus Santoso ◽

...

Keyword(s):

Global Warming ◽

El Niño ◽

El Nino ◽

Butterfly Effect

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Changes in Independency between Two Types of El Niño Events under a Greenhouse Warming Scenario in CMIP5 Models

Journal of Climate ◽

10.1175/jcli-d-14-00721.1 ◽

2015 ◽

Vol 28 (19) ◽

pp. 7561-7575 ◽

Cited By ~ 2

Author(s):

Yoo-Geun Ham ◽

Yerim Jeong ◽

Jong-Seong Kug

Keyword(s):

Global Warming ◽

El Niño ◽

El Nino ◽

Western Pacific ◽

Cmip5 Models ◽

Greenhouse Warming ◽

Central Pacific ◽

El Niño Events ◽

The Western Pacific ◽

El Nino Events

Abstract This study uses archives from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to investigate changes in independency between two types of El Niño events caused by greenhouse warming. In the observations, the independency between cold tongue (CT) and warm pool (WP) El Niño events is distinctively increased in recent decades. The simulated changes in independency between the two types of El Niño events according to the CMIP5 models are quite diverse, although the observed features are simulated to some extent in several climate models. It is found that the climatological change after global warming is an essential factor in determining the changes in independency between the two types of El Niño events. For example, the independency between these events is increased after global warming when the climatological precipitation is increased mainly over the equatorial central Pacific. This climatological precipitation increase extends convective response to the east, particularly for CT El Niño events, which leads to greater differences in the spatial pattern between the two types of El Niño events to increase the El Niño independency. On the contrary, in models with decreased independency between the two types of El Niño events after global warming, climatological precipitation is increased mostly over the western Pacific. This confines the atmospheric response to the western Pacific in both El Niño events; therefore, the similarity between them is increased after global warming. In addition to the changes in the climatological state after global warming, a possible connection of the changes in the El Niño independency with the historical mean state is discussed in this paper.

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Estimates of the Water Vapor Climate Feedback during El Niño–Southern Oscillation

Journal of Climate ◽

10.1175/2009jcli3052.1 ◽

2009 ◽

Vol 22 (23) ◽

pp. 6404-6412 ◽

Cited By ~ 26

Author(s):

A. E. Dessler ◽

S. Wong

Keyword(s):

Global Warming ◽

Water Vapor ◽

El Niño ◽

Climate Models ◽

El Nino ◽

Southern Oscillation ◽

Specific Humidity ◽

El Niño Southern Oscillation ◽

El Nino Southern Oscillation ◽

Water Vapor Feedback

Abstract The strength of the water vapor feedback has been estimated by analyzing the changes in tropospheric specific humidity during El Niño–Southern Oscillation (ENSO) cycles. This analysis is done in climate models driven by observed sea surface temperatures [Atmospheric Model Intercomparison Project (AMIP) runs], preindustrial runs of fully coupled climate models, and in two reanalysis products, the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) and the NASA Modern Era Retrospective-Analysis for Research and Applications (MERRA). The water vapor feedback during ENSO-driven climate variations in the AMIP models ranges from 1.9 to 3.7 W m−2 K−1, in the control runs it ranges from 1.4 to 3.9 W m−2 K−1, and in the ERA-40 and MERRA it is 3.7 and 4.7 W m−2 K−1, respectively. Taken as a group, these values are higher than previous estimates of the water vapor feedback in response to century-long global warming. Also examined is the reason for the large spread in the ENSO-driven water vapor feedback among the models and between the models and the reanalyses. The models and the reanalyses show a consistent relationship between the variations in the tropical surface temperature over an ENSO cycle and the radiative response to the associated changes in specific humidity. However, the feedback is defined as the ratio of the radiative response to the change in the global average temperature. Differences in extratropical temperatures will, therefore, lead to different inferred feedbacks, and this is the root cause of spread in feedbacks observed here. This is also the likely reason that the feedback inferred from ENSO is larger than for long-term global warming.

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Global warming in Amazonia: impacts and Mitigation

Acta Amazonica ◽

10.1590/s0044-59672009000400030 ◽

2009 ◽

Vol 39 (4) ◽

pp. 1003-1011 ◽

Cited By ~ 11

Author(s):

Philip Martin Fearnside

Keyword(s):

Climate Change ◽

Global Warming ◽

Forest Fires ◽

El Niño ◽

El Nino ◽

Cost Effective ◽

Climatic Conditions ◽

Carbon Accounting ◽

Amazon Forest ◽

Temperature Oscillations

Global warming has potentially catastrophic impacts in Amazonia, while at the same time maintenance of the Amazon forest offers one of the most valuable and cost-effective options for mitigating climate change. We know that the El Niño phenomenon, caused by temperature oscillations of surface water in the Pacific, has serious impacts in Amazonia, causing droughts and forest fires (as in 1997-1998). Temperature oscillations in the Atlantic also provoke severe droughts (as in 2005). We also know that Amazonian trees die both from fires and from water stress under hot, dry conditions. In addition, water recycled through the forest provides rainfall that maintains climatic conditions appropriate for tropical forest, especially in the dry season. What we need to know quickly, through intensified research, includes progress in representing El Niño and the Atlantic oscillations in climatic models, representation of biotic feedbacks in models used for decision-making about global warming, and narrowing the range of estimating climate sensitivity to reduce uncertainty about the probability of very severe impacts. Items that need to be negotiated include the definition of "dangerous" climate change, with the corresponding maximum levels of greenhouse gases in the atmosphere. Mitigation of global warming must include maintaining the Amazon forest, which has benefits for combating global warming from two separate roles: cutting the flow the emissions of carbon each year from the rapid pace of deforestation, and avoiding emission of the stock of carbon in the remaining forest that can be released by various ways, including climate change itself. Barriers to rewarding forest maintenance include the need for financial rewards for both of these roles. Other needs are for continued reduction of uncertainty regarding emissions and deforestation processes, as well as agreement on the basis of carbon accounting. As one of the countries most subject to impacts of climate change, Brazil must assume the leadership in fighting global warming.

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