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Marika M. Holland and Donald Perovich

Significant changes in the Arctic are underway with profound implications for the future. There is an opportunity to improve our ability to observe and understand ongoing changes in the Arctic sea ice cover and to project future changes through a greater synthesis of observations and models. There is a strong group of researchers observing Arctic sea ice and another strong group modeling Arctic sea ice, but these two groups have remained largely distinct. While each group is expert in its own

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Albert Gabric, Patricia Matrai, Graham Jones, and Julia Middleton

We examine the relationship between sea ice dynamics, phytoplankton biomass, and emissions of marine biogenic aerosols in both the Arctic and Southern Oceans. Marine biogenic aerosol (MBA) plays an important role in the radiative budget of remote marine atmospheres by potentially shaping regional climate ( McCoy et al. 2015 ). MBAs can influence cloud microphysical properties as cloud condensation nuclei (CCN), affecting cloud albedo and lifetime. However, despite three decades of research, the

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William L. Smith Jr., Christy Hansen, Anthony Bucholtz, Bruce E. Anderson, Matthew Beckley, Joseph G. Corbett, Richard I. Cullather, Keith M. Hines, Michelle Hofton, Seiji Kato, Dan Lubin, Richard H. Moore, Michal Segal Rosenhaimer, Jens Redemann, Sebastian Schmidt, Ryan Scott, Shi Song, John D. Barrick, J. Bryan Blair, David H. Bromwich, Colleen Brooks, Gao Chen, Helen Cornejo, Chelsea A. Corr, Seung-Hee Ham, A. Scott Kittelman, Scott Knappmiller, Samuel LeBlanc, Norman G. Loeb, Colin Miller, Louis Nguyen, Rabindra Palikonda, David Rabine, Elizabeth A. Reid, Jacqueline A. Richter-Menge, Peter Pilewskie, Yohei Shinozuka, Douglas Spangenberg, Paul Stackhouse, Patrick Taylor, K. Lee Thornhill, David van Gilst, and Edward Winstead

Through ARISE, NASA acquired unique aircraft data on clouds, atmospheric radiation and sea ice properties during the critical period between the sea ice minimum in late summer and autumn and the commencement of refreezing. Arctic sea ice decline is one of the most profound manifestations of contemporary climate change, and the loss has been accelerating in recent years as seen by regular extreme September minima and lengthening of the melt season by 5 days decade −1 ( Stroeve et al. 2012

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James A. Screen, Clara Deser, and Lantao Sun

Contrary to recent claims, North American cold extremes are expected to become less frequent as a result of continuing Arctic sea ice loss. In early January 2014, an Arctic air outbreak brought extreme cold to central and eastern North America. Record low minimum temperatures for the calendar date were set at many weather stations, including at Chicago, Illinois (O’Hare Airport, –26.7°C/–16°F, 6 January); New York, New York (Central Park, –15.6°C/4°F, 7 January); Washington, D.C. (Dulles

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E. Carmack, I. Polyakov, L. Padman, I. Fer, E. Hunke, J. Hutchings, J. Jackson, D. Kelley, R. Kwok, C. Layton, H. Melling, D. Perovich, O. Persson, B. Ruddick, M.-L. Timmermans, J. Toole, T. Ross, S. Vavrus, and P. Winsor

Small changes in the ways that the ocean transports heat to the overlying ice cover could have a substantial effect on future changes in Arctic ice cover. It was the best of ice, it was the worst of ice, It was the age of growth, it was the age of melt, It was the season of multiyear, it was the season of first year, We had thick ice before us, we had no ice before us. This paraphrasing, by Don Perovich, of Charles Dickens’s A Tale of Two Cities describes the startling changes in Arctic sea

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Mark A. Bourassa, Sarah T. Gille, Cecilia Bitz, David Carlson, Ivana Cerovecki, Carol Anne Clayson, Meghan F. Cronin, Will M. Drennan, Chris W. Fairall, Ross N. Hoffman, Gudrun Magnusdottir, Rachel T. Pinker, Ian A. Renfrew, Mark Serreze, Kevin Speer, Lynne D. Talley, and Gary A. Wick

High latitudes present extreme conditions for the measurement and estimation of air–sea and ice fluxes, limiting understanding of related physical processes and feedbacks that are important elements of the Earth's climate. High-latitude climate change can manifest itself in astonishing ways. Arctic sea ice extent at the end of the melt season in September is declining at a mean rate of 12% per decade, with record seasonal minima in 2007 and 2012 ( Comiso et al. 2008 ; Shawstack 2012 ). In 2001

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A. Mahoney, S. Gearheard, T. Oshima, and T. Qillaq

The accelerating retreat of Arctic sea ice in recent years highlights the need for improved monitoring efforts to provide information relevant to decision makers and stakeholders. Satellite data and global circulation models often lack details relevant to residents of Arctic communities, whose livelihoods can be profoundly affected by small changes in sea ice. As part of the Siku-Inuit-Hila (Sea Ice-People-Weather) project, we have established sea ice observation programs in three Arctic communities: Barrow, Alaska; Clyde River, Nunavut, Canada; and Qaanaaq, Greenland. By working with the communities to provide equipment and training, we have mitigated some of the difficulties involved in maintaining field programs in remote parts of the Arctic. We also created a framework for a two-way knowledge exchange between scientists and local sea ice experts. Results from the first season allow us to calculate rates of ice growth and ice melt at the upper and lower surfaces of the sea ice. The sea ice near Qaanaaq grew slowly during the end of winter before undergoing significant bottom melt. From this, we infer a significant source of ocean heat beneath the sea ice near Qaanaaq that was absent in the other communities. Findings such as these are vital for understanding how sea ice might respond on a local scale to global change, and local field observations are currently the only way to acquire the needed data. Close collaboration with Arctic residents can ensure consistent, quality data collection, the incorporation of local knowledge, and a better understanding of how changes affect Arctic communities.

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William L. Chapman and John E. Walsh

Feedbacks resulting from the retreat of sea ice and snow contribute to the polar amplification of the greenhouse warming projected by global climate models. A gridded sea-ice database, for which the record length is now approaching four decades for the Arctic and two decades for the Antarctic, is summarized here. The sea-ice fluctuations derived from the dataset are characterized by 1) temporal scales of several seasons to several years and 2) spatial scales of 30°–180° of longitude. The ice data are examined in conjunction with air temperature data for evidence of recent climate change in the polar regions. The arctic sea-ice variations over the past several decades are compatible with the corresponding air temperatures, which show a distinct warming that is strongest over northern land areas during the winter and spring. The temperature trends over the subarctic seas are smaller and even negative in the southern Greenland region. Statistically significant decreases of the summer extent of arctic ice are apparent in the sea-ice data, and new summer minima have been achieved three times in the past 15 years. There is no significant trend of ice extent in the Arctic during winter or in the Antarctic during any season. The seasonal and geographical changes of sea-ice coverage are consistent with the more recent greenhouse experiments performed with coupled atmosphere–ocean models.

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Kristina B. Katsaros and Robert A. Brown

The polar-orbiting satellite, Seasat, had been designed as an oceanographic satellite with little advance thought being given to atmospheric uses. However, the microwave instruments provided a rich source of data for studying atmospheric conditions. The simultaneous sampling by several instruments generated special benefits, a situation which to date has not been repeated. In this review we emphasize studies of midlatitude and tropical cyclones and regional weather and climate analyses. We also touch upon studies of long swell, sea ice, and continental ice sheets with Seasat data.

Many of these results of the Seasat mission were serendipitous. In preparation for the major NASA initiative for the next decade, the Earth Observing Satellite (EOS) program, we thought it timely to bring some of the Seasat experiences to the fore, since valuable lessons can be learned from the successes and the failures (or omissions) of the Seasat program. We have learned of: 1) the synergistic value of integrated, overlapping sampling by several instruments, 2) the invaluable contribution of carefully planned surface measurements, and 3) the importance of retaining flexibility in the system (enough data retention) to allow unexpected and innovative analysis techniques.

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Ed Blockley, Martin Vancoppenolle, Elizabeth Hunke, Cecilia Bitz, Daniel Feltham, Jean-François Lemieux, Martin Losch, Eric Maisonnave, Dirk Notz, Pierre Rampal, Steffen Tietsche, Bruno Tremblay, Adrian Turner, François Massonnet, Einar Ólason, Andrew Roberts, Yevgeny Aksenov, Thierry Fichefet, Gilles Garric, Doroteaciro Iovino, Gurvan Madec, Clément Rousset, David Salas y Melia, and David Schroeder

Toward Defining a Cutting-Edge Future for Sea Ice Modeling: An International Workshop What : Sea ice model developers and expert users met to discuss the future of sea ice modeling. When : 23–26 September 2019 Where : Laugarvatn, Iceland Earth system models (ESMs) include a sea ice component to physically represent sea ice changes and impacts on planetary albedo and ocean circulation ( Manabe and Stouffer 1980 ). Most contemporary sea ice models describe the sea ice pack as a continuum material

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