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Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)3 project was established in 2016 (www.ac3-tr.de/). It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, shipborne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data. For example, a distinct atmospheric moistening, an increase of regional storm activities, an amplified winter warming in the Svalbard and North Pole regions, and a decrease of sea ice thickness in the Fram Strait and of snow depth on sea ice have been identified. A positive trend of tropospheric bromine monoxide (BrO) column densities during polar spring was verified. Local marine/biogenic sources for cloud condensation nuclei and ice nucleating particles were found. Atmospheric–ocean and radiative transfer models were advanced by applying new parameterizations of surface albedo, cloud droplet activation, convective plumes and related processes over leads, and turbulent transfer coefficients for stable surface layers. Four modes of the surface radiative energy budget were explored and reproduced by simulations. To advance the future synthesis of the results, cross-cutting activities are being developed aiming to answer key questions in four focus areas: lapse rate feedback, surface processes, Arctic mixed-phase clouds, and airmass transport and transformation.

Together with sea ice, Arctic snow has experienced vast changes during the last decade due to a warming climate. Thus, it is relevant to study the past and present changes of Arctic snow to understand the implications to the sea ice component, precipitation, heat and radiation budgets. In this study, we analyze the changes of snow depth between 2000 and 2013 at regional scale represented in an Arctic coupled sea ice-general circulation model. We evaluate the model performance by direct comparison of the modeled snow depths (hs_mod) to snow depths from radar measurements from the NASA Operation IceBridge (hs_OIB) during the flight campaigns completed from 2009 to 2013. Despite the description of the snow in our model is simple (i.e. single layer without explicit snow redistribution processes) as in many current sea-ice models; the latitudinal distribution of hs_mod in the western Arctic is in good agreement to observations. The hs_mod is on average 3 cm thicker than hs_OIB in latitudes > 76° N. According to the model results, the hs in 2013 decreased 21 % with respect to the multi-year mean between 2000 and 2013. This snow reduction occurred mainly in FYI dominated areas, and is in good agreement to the year-to-year loss of sea ice, also well reproduced by the model. In a simple snow mass budget, our results show that 65 % of the yearly accumulated snow is lost by sublimation and snowmelt due to the heat transfer between the snow/ice interface and the atmosphere. Although the snow layer accumulates again every year, the long-term reduction in the summer sea-ice extent ultimately affects the maximum spring accumulation of snow. The model results exhibit a last decade thinning of the snowpack that is however one order of magnitude lower than previous estimates based on radar measurements. We suggest that the later is partially due to the lack of explicit snow redistribution processes in the model, emphasizing the need to include these in current sea-ice models to improve the snow representations.

The recent thinning and shrinking of the Arctic sea ice cover has increased the interest in seasonal sea ice forecasts. Typical tools for such forecasts are numerical models of the coupled ocean sea ice system such as the North Atlantic/Arctic Ocean Sea Ice Model (NAOSIM). The model uses as input the initial state of the system and the atmospheric boundary condition over the forecasting period. This study investigates the potential of remotely sensed ice thickness observations in constraining the initial model state. For this purpose it employs a variational assimilation system around NAOSIM and the Alfred Wegener Institute's CryoSat-2 ice thickness product in conjunction with the University of Bremen's snow depth product and the OSI SAF ice concentration and sea surface temperature products. We investigate the skill of predictions of the summer ice conditions starting in March for three different years. Straightforward assimilation of the above combination of data streams results in slight improvements over some regions (especially in the Beaufort Sea) but degrades the over-all fit to independent observations. A considerable enhancement of forecast skill is demonstrated for a bias correction scheme for the CryoSat-2 ice thickness product that uses a spatially varying scaling factor.

The combination of multi-disciplinary sea ice science and the rising demand of society for up-to-date information and user customized products on climate change emphasis the need for addressing the challenges posed by environmental change in the Polar Regions by means of creating new ways of communication. The new knowledge platform “meereisportal.de” is a contribution to the cross-linking of scientifically qualified information on climate change and focuses deliberately on the theme: “sea ice” in both Polar Regions. With “meereisportal. de” the science opens to changing societal demands and goes new ways of communication between science and society. “meereisportal. de” is the first comprehensive German speaking knowledge platform on sea ice that went online 2013. It was developed in the frame of the Helmholtz Climate Initiative, Regional Climate Change (REKLIM) as a joint project of the University of Bremen (Institute of Environmental Physics) and the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research under the management of the Helmholtz Regional Climate Office for Polar Regions and Sea Level change. This paper describes the concept and the development of the knowledge platform, different usage examples and user-specific products. Moreover, an outlook on the planned activities in the future will be given. Die Kombination der zunehmend multi-disziplinären Meereisforschung und die steigende Nachfrage der Gesellschaft nach aktuellen Informationen und benutzerorientierten Produkten zum Thema Klimawandel erfordert neue Wege der Wissenskommunikation, um den Herausforderungen der zunehmenden Umweltveränderungen, insbesondere in den Polarregionen, zu begegnen. Die neue Wissensplattform “meereisportal.de” ist ein Beitrag zum Vernetzen von wissenschaftlich qualifizierten Fachinformationen zum Thema Klimawandel und fokussiert dabei bewusst auf ein Thema: “Meereis” in beiden Polargebieten. Mit “meereisportal.de” öffnet sich die Wissenschaft gegenüber sich verändernden gesellschaftlichen Anforderungen und geht neue Wege der Kommunikation zwischen Wissenschaft und Gesellschaft. “meereisportal. de” ist 2013 als erste umfassende, deutschsprachige Wissensplattform rund um das Thema Meereis in der Arktis und Antarktis online gegangen. Sie wurde im Rahmen des Helmholtz-Verbundes Regionale Klimaveränderungen (REKLIM) als Gemeinschaftsprojekt der Universität Bremen (Institut für Umweltphysik) und des Alfred-Wegener-Institutes, Helmholtz-Zentrum für Polar- und Meeresforschung unter der Federführung des regionalen Helmholtz Klimabüros für Polargebiete und Meeresspiegelanstieg entwickelt. Dieser Beitrag beschreibt die Entstehung, das Konzept und die Entwicklung der Wissensplattform, verschiedene Anwendungsbeispiele sowie nutzerspezifische Produkte. Darüber hinaus wird ein Ausblick über die in Zukunft geplanten Aktivitäten gegeben.

Sea ice and snow on sea ice to a large extent determine the surface heat budget in the Arctic Ocean. In spite of the advances in modeling sea-ice thermodynamics, a good number of models still rely on simple parameterizations of the thermodynamics of ice and snow. Based on simulations with an Arctic sea-ice model coupled to an ocean general circulation model, we analyzed the impact of changing two sea-ice parameterizations: (1) the prescribed ice thickness distribution (ITD) for surface heat budget calculations, and (2) the description of the snow layer. For the former, we prescribed a realistic ITD derived from airborne electromagnetic induction sounding measurements. For the latter, two different types of parameterizations were tested: (1) snow thickness independent of the sea-ice thickness below, and (2) a distribution proportional to the prescribed ITD. Our results show that changing the ITD from seven uniform categories to fifteen nonuniform categories derived from field measurements, and distributing the snow layer according to the ITD, leads to an increase in average Arctic-wide ice thickness by 0.56 m and an increase by 1 m in the Canadian Arctic Archipelago and Canadian Basin. This increase is found to be a direct consequence of 524 km3 extra thermodynamic growth during the months of ice formation (January, February, and March). Our results emphasize that these parameterizations are a key factor in sea-ice modeling to improve the representation of the sea-ice energy balance.

IPY2012 Conference Montréal. From Knowledge to Action, 22-27 April 2012, Montréal, Canada, The marine environment of the Arctic Ocean is under profound transformation, as clearly shown by observations and model predictions across a range of disciplines. The rapid decline in sea ice extent and volume during the boreal summers is a prime example. To improve our understanding of the key physical processes that drive change in this region, it is crucial to monitor the complex ocean-cryosphere-atmosphere system. This presentation explores how sea ice is changing in this region by using a combined observational and modeling approach that builds heavily on the latest technological advances in Space Geodesy. We have developed a high-precision (i.e., few cm position accuracy), GPS-based autonomous platform suited to the challenging Arctic Ocean environment that enables determination of sea ice motions in three-dimensions with hightemporal sampling and, when deployed as a network, also high-spatial density. The platform includes a sea ice freeboard sensor and two-way communications, thus also enabling near-real time monitoring and remote data retrieval. We have deployed several prototypes of such platform for limited durations both in the Arctic Ocean and the Southern Ocean since 2009, and two full-blown, long-term systems, on the Chukchi Sea, during the boreal summer of 2011. Although monitoring of sea ice motions in this fast changing region goes back to the early days of satellite observations, these systems bring out a level of spatio-temporal detail that has never been seen before, which in turn allows us to question our present understanding of sea ice dynamics. We will describe the technology behind this novel platform, which could also be adapted to other applications that require sustained operations and observations in the Arctic environment, and present results pertaining to sea ice dynamics, Arctic Ocean tides, ocean dynamic topography, ocean currents, and sea ice freeboard, thickness, and mass balance, from the analysis of the GPS and freeboard data collected by those systems

Polarforschung

Polarforschung