The Decadal Variability of the Pacific with the MRI Coupled Models

Previous studies have investigated the centennial and multidecadal trends of the Pacific and Indian Ocean Walker cells (WCs) during the past century, but have obtained no consensus owing to data uncertainties and weak signals of the long-term trends. This paper focuses on decadal variability (periods of one to few decades) by first documenting the variability of the WCs and warm-pool convection, and their covariability since the 1960s, using in situ and satellite observations and reanalysis products. The causes for the variability and covariability are then explored using a Bayesian dynamic linear model, which can extract nonstationary effects of climate modes. The warm-pool convection exhibits apparent decadal variability, generally covarying with the Indian and Pacific Ocean WCs during winter (November–April) with enhanced convection corresponding to intensified WCs, and the Indian–Pacific WCs covary. During summer (May–October), the warm-pool convection still highly covaries with the Pacific WC but does not covary with the Indian Ocean WC, and the Indian–Pacific WCs are uncorrelated. The wintertime coherent variability results from the vital influence of ENSO decadal variation, which reduces warm-pool convection and weakens the WCs during El Niño–like conditions. During summer, while ENSO decadal variability still dominates the Pacific WC, decadal variations of ENSO, the Indian Ocean dipole, Indian summer monsoon convection, and tropical Indian Ocean SST have comparable effects on the Indian Ocean WC overall, with monsoon convection having the largest effect since the 1990s. The complex causes for the Indian Ocean WC during summer result in its poor covariability with the Pacific WC and warm-pool convection.

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Decadal variability of twentieth-century El Niño and La Niña occurrence from observations and IPCC AR4 coupled models

Geophysical Research Letters ◽

10.1029/2009gl037929 ◽

2009 ◽

Vol 36 (11) ◽

Cited By ~ 50

Author(s):

Xin Wang ◽

Dongxiao Wang ◽

Wen Zhou

Keyword(s):

Twentieth Century ◽

El Niño ◽

Decadal Variability ◽

El Nino ◽

La Niña ◽

Coupled Models ◽

La Nina ◽

Ipcc Ar4

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North Pacific Subtropical Mode Water Controlled by the Atlantic Multi-Decadal Variability

10.5194/egusphere-egu2020-235 ◽

2020 ◽

Author(s):

Baolan wu ◽

Xiaopei lin ◽

Lisan yu

Keyword(s):

Pacific Ocean ◽

North Pacific ◽

Decadal Variability ◽

Heat Content ◽

Northwestern Pacific ◽

Mode Water ◽

Subtropical Mode Water ◽

The North ◽

Mean Temperature ◽

The Pacific

The North Pacific Subtropical Mode Water (mode water hereafter) is a vertically homogeneous thermocline water mass, occupying the entire subtropical Western Pacific Ocean. By transporting mass, heat and nutrients from the surface into the subsurface ocean, it provides memory of climate variability and is a potential source of predictability. Previous studies attributed decadal variability of the mode water mean temperature to the Pacific Decadal Oscillation (PDO). Using available observations and reanalysis data, here we show that decadal to multi-decadal variability of the mode water mean temperature is controlled by the Atlantic Multi-Decadal Variability (AMV) instead. During an AMV positive phase, warm sea surface temperatures (SSTs) in the north Atlantic Ocean weaken the subtropical North Pacific westerlies, and the anomalous easterlies in the subtropical west Pacific drive an anomalous northward Ekman transport of warm water into the mode water formation area. This increases the mode water temperature through subduction, driving variability of the upper-layer ocean heat content and fish catches in the Northwestern Pacific. This mechanism is supported by a long pre-industrial model simulation with multiple AMV cycles and by a Pacemaker model experiment, in which the AMV forcing alone is shown to drive the variability of the mode water. Our finding suggests that the AMV is an important driver for decadal climate and ecosystem variability and provides memory for prediction in the Pacific Ocean.

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Impact of the Pacific mean SST bias to the Atlantic-Pacific teleconnection

10.5194/egusphere-egu2020-7407 ◽

2020 ◽

Author(s):

Chen Li ◽

Dietmar Dommenget ◽

Shayne McGregor

Keyword(s):

Decadal Variability ◽

Atmospheric Stability ◽

Low Frequency ◽

Trade Wind ◽

Atmospheric Teleconnection ◽

Surface Warming ◽

Sst Bias ◽

Pacific Decadal Variability ◽

The Pacific ◽

Low Frequency Variability

A robust eastern tropical Pacific surface temperature cooling trend along with the strengthening of Pacific trade wind is evident across different observations since late 1990s, which is considered as a pronounced contributor to the slowdown in global surface warming. However, most CMIP5 historical simulations failed to reproduce this La Ni&#241;a-like change. Previous studies have attributed this discrepancy between the multi-model simulations and the observations to the underrepresentation of Pacific low-frequency variability together with the misrepresentation of inter-basin forcing response. The underlying reasons remain unclear. Here, we investigate a hypothesis that common Pacific mean SST bias may diminish the Pacific-Atlantic atmospheric teleconnection and further contribute to the underestimated eastern Pacific cooling. Model results suggest that the CMIP5-like Pacific bias acts to reduce the Atlantic heating response by strengthening the atmospheric stability over the Atlantic region and therefore weaken the trans-basin variability. In addition, the Pacific bias simulation with a strong SST cold tongue substantially undermined the positive zonal wind feedback, which also contributes to the underestimated Pacific cooling response. Future efforts aim at reducing the model mean state biases may significantly help to improve the simulation skills of the trans-basin teleconnection, Pacific decadal variability, and the associated Pacific dynamics.&#160;&#160; &#160;&#160;&#160;

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The Mid-1970s Climate Shift in the Pacific and the Relative Roles of Forced versus Inherent Decadal Variability

Journal of Climate ◽

10.1175/2008jcli2552.1 ◽

2009 ◽

Vol 22 (3) ◽

pp. 780-792 ◽

Cited By ~ 146

Author(s):

Gerald A. Meehl ◽

Aixue Hu ◽

Benjamin D. Santer

Keyword(s):

Fossil Fuels ◽

Climate Model ◽

Decadal Variability ◽

Climate System ◽

Positive Phase ◽

Significant Shift ◽

Climate Shift ◽

External Forcings ◽

The Pacific ◽

The 1960S

Abstract A significant shift from cooler to warmer tropical Pacific sea surface temperatures (SSTs), part of a pattern of basinwide SST anomalies involved with a transition to the positive phase of the Interdecadal Pacific Oscillation (IPO), occurred in the mid-1970s with effects that extended globally. One view is that this change was entirely natural and was a product of internally generated decadal variability of the Pacific climate system. However, during the mid-1970s there was also a significant increase of global temperature and changes to a number of other quantities that have been associated with changes in external forcings, particularly increases of greenhouse gases from the burning of fossil fuels. Analysis of observations, an unforced control run from a global coupled climate model, and twentieth-century simulations with changes in external forcings show that the observed 1970s climate shift had a contribution from changes in external forcing superimposed on what was likely an inherent decadal fluctuation of the Pacific climate system. Thus, this inherent decadal variability associated with the IPO delayed until the 1970s what likely would have been a forced climate shift in the 1960s from a negative to positive phase of the IPO.

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Reconciling Theories for Human and Natural Attribution of Recent East Africa Drying

Journal of Climate ◽

10.1175/jcli-d-16-0558.1 ◽

2017 ◽

Vol 30 (6) ◽

pp. 1939-1957 ◽

Cited By ~ 15

Author(s):

Andrew Hoell ◽

Martin Hoerling ◽

Jon Eischeid ◽

Xiao-Wei Quan ◽

Brant Liebmann

Keyword(s):

Global Warming ◽

East Africa ◽

Decadal Variability ◽

Coupled Model ◽

Western Pacific ◽

East African ◽

Coupled Models ◽

Central Pacific ◽

Model Simulations ◽

African Rainfall

Abstract Two theories for observed East Africa drying trends during March–May 1979–2013 are reconciled. Both hypothesize that variations in tropical sea surface temperatures (SSTs) caused East Africa drying. The first invokes a mainly human cause resulting from sensitivity to secular warming of Indo–western Pacific SSTs. The second invokes a mainly natural cause resulting from sensitivity to a strong articulation of ENSO-like Pacific decadal variability involving warming of the western Pacific and cooling of the central Pacific. Historical atmospheric model simulations indicate that observed SST variations contributed significantly to the East Africa drying trend during March–May 1979–2013. By contrast, historical coupled model simulations suggest that external radiative forcing alone, including the ocean’s response to that forcing, did not contribute significantly to East Africa drying. Recognizing that the observed SST variations involved a commingling of natural and anthropogenic effects, this study diagnosed how East African rainfall sensitivity was conditionally dependent on the interplay of those factors. East African rainfall trends in historical coupled models were intercompared between two composites of ENSO-like decadal variability, one operating in the early twentieth century before appreciable global warming and the other in the early twenty-first century of strong global warming. The authors find the coaction of global warming with ENSO-like decadal variability can significantly enhance 35-yr East Africa drying trends relative to when the natural mode of ocean variability acts alone. A human-induced change via its interplay with an extreme articulation of natural variability may thus have been key to Africa drying; however, these results are speculative owing to differences among two independent suites of coupled model ensembles.

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Indian Ocean Decadal Variability: A Review

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-13-00028.1 ◽

2014 ◽

Vol 95 (11) ◽

pp. 1679-1703 ◽

Cited By ~ 117

Author(s):

Weiqing Han ◽

Jérôme Vialard ◽

Michael J. McPhaden ◽

Tong Lee ◽

Yukio Masumoto ◽

...

Keyword(s):

Indian Ocean ◽

Climate Variability ◽

Decadal Variability ◽

International Scientific Community ◽

Climate Research ◽

Physical Mechanisms ◽

The Pacific ◽

Climatic Impacts ◽

The Indian Ocean ◽

Multidecadal Climate Variability

The international scientific community has highlighted decadal and multidecadal climate variability as a priority area for climate research. The Indian Ocean rim region is home to one-third of the world's population, mostly living in developing countries that are vulnerable to climate variability and to the increasing pressure of anthropogenic climate change. Yet, while prominent decadal and multidecadal variations occur in the Indian Ocean, they have been less studied than those in the Pacific and Atlantic Oceans. This paper reviews existing literature on these Indian Ocean variations, including observational evidence, physical mechanisms, and climatic impacts. This paper also identifies major issues and challenges for future Indian Ocean research on decadal and multidecadal variability.

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