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Weiqing Han, Jérôme Vialard, Michael J. McPhaden, Tong Lee, Yukio Masumoto, Ming Feng, and Will P.M. de Ruijter

Improved definition and understanding of decadal timescale variability in the Indian Ocean region will support climate prediction efforts and have the potential to benefit a large percentage of the world's population living in Indian Ocean rim countries and elsewhere around the globe. Existing records of upper-ocean temperature exhibit clear fluctuations at time scales ranging from one to a few decades, which for simplicity we refer collectively to as “decadal variability” in this paper 1 (see

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Christophe Cassou, Yochanan Kushnir, Ed Hawkins, Anna Pirani, Fred Kucharski, In-Sik Kang, and Nico Caltabiano

DECADAL PHENOMENA AND THEIR CHARACTERISTICS. The slowdown in the rate of global surface warming in the early 2000s, and especially its regional characteristics, highlights the importance of decadal climate variability (DCV) as a modulator of long-term warming trends due to ever-increasing anthropogenic forcings ( Medhaug et al. 2017 ). This event, which was termed in the scientific and public domain as a “pause” or “hiatus” in global warming ( Lewandowsky et al. 2016 ), was argued by scientists

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H. Nakamura, G. Lin, and T. Yamagata

Decadal wintertime variability in the North Pacific climate system observed over the last few decades is documented. The decadal sea surface temperature (SST) variability is found to be concentrated around two major oceanic fronts. The variability around the subtropical front, accompanied by the anomalous subtropical high, exhibits strong negative simultaneous correlation with the tropical SST variability, but that around the subarctic front does not. In fact, cooling around the subarctic front in the mid-1970s cannot be attributed to the influence through the atmosphere of tropical warming that occurred about two years later. During the coolest period around the subarctic front in the mid-1980s, the enhanced surface westerlies associated with the intensified Aleutian low seemed to reinforce the underlying SST anomalies. The westerlies tended to be substantially weaker during the warmest period around 1970. These findings are suggestive of self-maintaining mechanisms inherent to the northern North Pacific climate system for the decadal variability.

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Neil J. Holbrook, Jianping Li, Matthew Collins, Emanuele Di Lorenzo, Fei-Fei Jin, Thomas Knutson, Mojib Latif, Chongyin Li, Scott B. Power, Rhonghui Huang, and Guoxiong Wu

The International Commission on Climate (ICCL), one of 10 international commissions of the International Association of Meteorology and Atmospheric Sciences (IAMAS) of the International Union of Geodesy and Geophysics (IUGG), held an Expert Assessment Workshop on “Decadal Climate Variability and Cross-Scale Interactions” in Beijing, China, from 16 to 17 April 2013. The workshop aimed to assess and document key issues and knowledge gaps associated with decadal-scale climate variability and cross

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Amy Solomon, Lisa Goddard, Arun Kumar, James Carton, Clara Deser, Ichiro Fukumori, Arthur M. Greene, Gabriele Hegerl, Ben Kirtman, Yochanan Kushnir, Matthew Newman, Doug Smith, Dan Vimont, Tom Delworth, Gerald A. Meehl, and Timothy Stockdale

Abstract

Given that over the course of the next 10–30 years the magnitude of natural decadal variations may rival that of anthropogenically forced climate change on regional scales, it is envisioned that initialized decadal predictions will provide important information for climate-related management and adaptation decisions. Such predictions are presently one of the grand challenges for the climate community. This requires identifying those physical phenomena—and their model equivalents—that may provide additional predictability on decadal time scales, including an assessment of the physical processes through which anthropogenic forcing may interact with or project upon natural variability. Such a physical framework is necessary to provide a consistent assessment (and insight into potential improvement) of the decadal prediction experiments planned to be assessed as part of the IPCC's Fifth Assessment Report.

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Vikram Mehta, Yochanan Kushnir, Judith Lean, David Legler, Roger Lukas, Andrey Proshutinsky, Norman Rosenberg, Hans von Storch, Paul Schopf, and Warren White
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Robert Wood, Matthew Wyant, Christopher S. Bretherton, Jasmine Rémillard, Pavlos Kollias, Jennifer Fletcher, Jayson Stemmler, Simone de Szoeke, Sandra Yuter, Matthew Miller, David Mechem, George Tselioudis, J. Christine Chiu, Julian A. L. Mann, Ewan J. O’Connor, Robin J. Hogan, Xiquan Dong, Mark Miller, Virendra Ghate, Anne Jefferson, Qilong Min, Patrick Minnis, Rabindra Palikonda, Bruce Albrecht, Ed Luke, Cecile Hannay, and Yanluan Lin

, effective radius, and cloud-top temperature and height ( Minnis et al. 2008 ). CLOUD AND METEOROLOGICAL VARIABILITY. The specific CAP-MBL science questions ( Table 1 ) include two focused on the impact of synoptic and seasonal variability on clouds and aerosols. To begin to address these, we note a marked seasonality in the surface pressure patterns near Graciosa ( Figs. 2a,b ). The winter season exhibits a strong meridional gradient of surface pressure between the semipermanent Icelandic low and the

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C.J.C Reason, W LANDMAN, and W TENNANT

A review of the interannual to interdecadal variability of the southern African region and its links with the Atlantic is given. Emphasis is placed on modes such as the Benguela Nĩno that develop within the Atlantic and may have some predictability. Seasonal forecasting and climate prediction efforts within the region are discussed. Most southern African countries rely on a combination of products obtained overseas and simple statistical methods. GCM based forecasts and statistical downscaling of their outputs are used operationally in South Africa and also applied to some neighboring countries. A review of these downscaling efforts and their various applications is given.

Research is also taking place into the predictability of quantities such as the onset of the rainy season (which appears to be associated with anomalous South Atlantic anticyclonic ridging) and dry spell frequencies within it. These parameters are often more useful to farmers in the region than forecasting above- or belowaverage seasonal rainfall totals. A strong link between dry spells and Nĩno-3.4 SST is evident for certain regions of southern Africa, suggesting that some predictability exists. This link is weaker for countries like Namibia and Angola that border the Atlantic than for southeastern Africa.

It is concluded that some aspects of southern African climate variability may have predictability but considerably more research is needed to better understand the influence of variability over the Atlantic. An added concern is the ongoing reduction in data collection in many parts of southern Africa. This reduction has serious implications for model development and validation, and for the accuracy of reanalysis products.

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Luke L. B. Davis, David W. J. Thompson, John J. Kennedy, and Elizabeth C. Kent

Biases in sea surface temperature observations lead to larger uncertainties in our understanding of mid- to late-twentieth-century climate variability than previously thought. The surface of the World Ocean warmed by ∼0.75 K from 1900 to 2016, but the warming did not occur monotonically: temperatures increased during the first half of the twentieth century, decreased slightly during the decades following World War II, and increased rapidly after ∼1975 ( Hartmann et al. 2013 ). The decreases in

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Gerald A. Meehl, Lisa Goddard, George Boer, Robert Burgman, Grant Branstator, Christophe Cassou, Susanna Corti, Gokhan Danabasoglu, Francisco Doblas-Reyes, Ed Hawkins, Alicia Karspeck, Masahide Kimoto, Arun Kumar, Daniela Matei, Juliette Mignot, Rym Msadek, Antonio Navarra, Holger Pohlmann, Michele Rienecker, Tony Rosati, Edwin Schneider, Doug Smith, Rowan Sutton, Haiyan Teng, Geert Jan van Oldenborgh, Gabriel Vecchi, and Stephen Yeager

decades in advance ( Barsugli et al. 2009 ; Means et al. 2010 ). Regional climate variability and change involving temperature and precipitation are important inputs for those decisions, and it is on those time scales of interest to water managers that decadal climate prediction is being applied as noted above. One question that could be asked is do current decadal climate predictions have sufficient skill or reliability on those time and space scales to be useful in helping water managers make

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