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Filippo Giorgi, Erika Coppola, Daniela Jacob, Claas Teichmann, Sabina Abba Omar, Moetasim Ashfaq, Nikolina Ban, Katharina Bülow, Melissa Bukovsky, Lars Buntemeyer, Tereza Cavazos, James Ciarlo`, Rosmeri Porfirio da Rocha, Sushant Das, Fabio di Sante, Jason P. Evans, Xuejie Gao, Graziano Giuliani, Russell H. Glazer, Peter Hoffmann, Eun-Soon Im, Gaby Langendijk, Ludwig Lierhammer, Marta Llopart, Sebastial Mueller, Rosa Luna-Nino, Rita Nogherotto, Emanuela Pichelli, Francesca Raffaele, Michelle Reboita, Diana Rechid, Armelle Remedio, Thomas Remke, Windmanagda Sawadogo, Kevin Sieck, José Abraham Torres-Alavez, and Torsten Weber

The Coordinated Regional Climate Downscaling Experiment (CORDEX) was created in the late 2000s with the overarching vision to advance climate downscaling science through global partnerships and coordination ( Giorgi et al. 2009 ; Gutowski et al. 2016 ). Its main goals are to provide a common modeling framework to (i) improve understanding of regional to local processes and feedbacks, and how they affect regional climate variability and change; (ii) assess and improve different regional

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John H. Seinfeld, Gregory R. Carmichael, Richard Arimoto, William C. Conant, Frederick J. Brechtel, Timothy S. Bates, Thomas A. Cahill, Antony D. Clarke, Sarah J. Doherty, Piotr J. Flatau, Barry J. Huebert, Jiyoung Kim, Krzysztof M. Markowicz, Patricia K. Quinn, Lynn M. Russell, Philip B. Russell, Atsushi Shimizu, Yohei Shinozuka, Chul H. Song, Youhua Tang, Itsushi Uno, Andrew M. Vogelmann, Rodney J. Weber, Jung-Hun Woo, and Xiao Y. Zhang

Although continental-scale plumes of Asian dust and pollution reduce the amount of solar radiation reaching the earth's surface and perturb the chemistry of the atmosphere, our ability to quantify these effects has been limited by a lack of critical observations, particularly of layers above the surface. Comprehensive surface, airborne, shipboard, and satellite measurements of Asian aerosol chemical composition, size, optical properties, and radiative impacts were performed during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) study. Measurements within a massive Chinese dust storm at numerous widely spaced sampling locations revealed the highly complex structure of the atmosphere, in which layers of dust, urban pollution, and biomass- burning smoke may be transported long distances as distinct entities or mixed together. The data allow a first-time assessment of the regional climatic and atmospheric chemical effects of a continental-scale mixture of dust and pollution. Our results show that radiative flux reductions during such episodes are sufficient to cause regional climate change.

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Marlene Kretschmer, Samantha V. Adams, Alberto Arribas, Rachel Prudden, Niall Robinson, Elena Saggioro, and Theodore G. Shepherd

models. For example, huge ensembles can be needed to detect (often only small) teleconnection signals ( Smith et al. 2020 ). Comparing the causal effects is more efficient ( Kretschmer et al. 2020 ); it can moreover shed light on the dynamical sources of model differences and should help in understanding potential signal-to-noise issues ( Scaife and Smith 2018 ). Quantifying teleconnections in climate model ensembles can also help to reduce uncertainties of regional weather and climate predictions

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Peter J. Sousounis and J. Michael Fritsch

A high-resolution numerical model is employed to examine effects of the Great Lakes aggregate, defined to be the five major Great Lakes, on regional and synoptic-scale weather. Simulations wherein the effects of the lakes are included and then excluded are performed on a selected cold air outbreak episode during late autumn when the lakes are still ice-free.

Examination of the differences between the model simulations reveals that several dynamical effects result from heating and moistening by the lake aggregate. These effects are manifested primarily in the form of a 4-km-deep, 2000-km-wide, lake-aggregate mesoscaie disturbance (circulation) that develops slowly over the region. The simulated lake-aggregate circulation splits a synoptic-scale high into two distinct centers and redirects and intensifies a weak synoptic-scale low, as verified by existing observations. These modifications of the synoptic-scale environment result in additional precipitation over, downstream, and upwind from the lakes.

The model simulations also reveal that the developing lake-aggregate circulation influences significantly the lake shore surface winds. In some locations, the surface winds switch from onshore to offshore or vice versa. Because it is well known from observations that the location and orientation of lake-induced snow bands are very sensitive to the low-level wind direction over the lakes, it is concluded that the exact locations of heavy snowfall are the result of a complex multiscale interaction among circulations on three different scales: synoptic, individual lake, and lake aggregate.

In addition to the developing primary lake-aggregate circulation, a secondary dynamic response appears at a distant location, adjacent to the eastern seaboard. The organization of this secondary circulation suggests that the lakes may play a direct role in some cases of East Coast cyclogenesis.

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Marina Baldissera Pacchetti, Suraje Dessai, Seamus Bradley, and David A. Stainforth

scientific information differently in the decision-making process ( Dessai and van der Sluijs 2007 ). Nevertheless, whenever scientific climate information is used in adaptation, “quality” is considered to be an essential characteristic that this information should have (e.g., Lu 2011 ; Wilby et al. 2009 ; for a general overview on quality of science for policy, see Funtowicz and Ravetz 1990 ). The kind of long-term regional climate information that is increasingly important for decision-makers (see

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Peter Knippertz, Hugh Coe, J. Christine Chiu, Mat J. Evans, Andreas H. Fink, Norbert Kalthoff, Catherine Liousse, Celine Mari, Richard P. Allan, Barbara Brooks, Sylvester Danour, Cyrille Flamant, Oluwagbemiga O. Jegede, Fabienne Lohou, and John H. Marsham

reacting with biogenic emissions can lead to enhanced ozone and acid production outside of urban conglomerations ( Marais et al. 2014 ), with detrimental effects on humans, animals, and plants (both natural and crops). The small-scale farming immediately to the north (and thus downstream) of the cities along the Guinea Coast is important for food production and would be seriously affected by degraded air quality. Regional Climate: Primary and secondary aerosol particles produced from biogenic and

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Jinyuan Xin, Yuesi Wang, Yuepeng Pan, Dongsheng Ji, Zirui Liu, Tianxue Wen, Yinghong Wang, Xingru Li, Yang Sun, Jie Sun, Pucai Wang, Gehui Wang, Xinming Wang, Zhiyuan Cong, Tao Song, Bo Hu, Lili Wang, Guiqian Tang, Wenkang Gao, Yuhong Guo, Hongyan Miao, Shili Tian, and Lu Wang

play an important role in global and regional climate change through direct and indirect effects. The direct effects influence the radiation and energy budget of Earth, mainly by absorbing and scattering solar and terrestrial radiation ( Dubovik et al. 2002 ; Menon 2004 ). The indirect effects, however, are more complicated. Aerosols can act as cloud condensation nuclei (CCN), thereby participating in the process of cloud formation, evolution, and dissipation, which changes the microphysical

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Simone Tilmes, Jadwiga H. Richter, Ben Kravitz, Douglas G. MacMartin, Michael J. Mills, Isla R. Simpson, Anne S. Glanville, John T. Fasullo, Adam S. Phillips, Jean-Francois Lamarque, Joseph Tribbia, Jim Edwards, Sheri Mickelson, and Siddhartha Ghosh

An overview is presented of the GLENS project, a community-wide effort enabling analyses of global and regional changes from stratospheric aerosol geoengineering in the presence of internal climate variability. Solar geoengineering using stratospheric sulfate aerosols has been discussed as a potential means of deliberately offsetting some of the effects of climate change ( Crutzen 2006 ). Various model studies have demonstrated that reducing incoming solar radiation globally can offset the

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C. R. Mechoso, R. Wood, R. Weller, C. S. Bretherton, A. D. Clarke, H. Coe, C. Fairall, J. T. Farrar, G. Feingold, R. Garreaud, C. Grados, J. McWilliams, S. P. de Szoeke, S. E. Yuter, and P. Zuidema

scales. The SEP is very important in many ways. The region produces nearly a fifth of the global fish catch ( Sherman and Hempel 2008 ), and variations in its climate can have global reach through teleconnections and aerosol indirect effects. The SEP is characterized by strong coastal ocean upwelling, the coldest sea surface temperatures (SSTs) at comparable latitudes, the planet's most extensive subtropical stratocumulus deck, and a high and steep cordillera to the east ( Fig. 1 ). The regional

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Catherine A. Senior, John H. Marsham, Ségolène Berthou, Laura E. Burgin, Sonja S. Folwell, Elizabeth J. Kendon, Cornelia M. Klein, Richard G. Jones, Neha Mittal, David P. Rowell, Lorenzo Tomassini, Théo Vischel, Bernd Becker, Cathryn E. Birch, Julia Crook, Andrew J. Dougill, Declan L. Finney, Richard J. Graham, Neil C. G. Hart, Christopher D. Jack, Lawrence S. Jackson, Rachel James, Bettina Koelle, Herbert Misiani, Brenda Mwalukanga, Douglas J. Parker, Rachel A. Stratton, Christopher M. Taylor, Simon O. Tucker, Caroline M. Wainwright, Richard Washington, and Martin R. Willet

features, particularly tropical convection or “storm” cells. Research studies and weather forecasting over Africa have made use of models that explicitly capture convection for some years (see the “Science discoveries” section). However, in the global and regional models commonly used to inform adaptation, such as from the Coupled Model Intercomparison Project (CMIP) or Coordinated Regional Climate Downscaling Experiment (CORDEX), only the bulk effects of convection over the model grid scale (typically

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