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The school was held at the Abisko Scientific Research Station in northern Sweden. It brought together 29 Ph.D. students and early-career researchers from 16 countries. It was a joint initiative from the World Weather Research Programme (WWRP)-Polar Prediction Project, the World Climate Research Program (WCRP)-Polar Climate Predictability Initiative, and the Bolin Centre for Climate Research. In this framework, an overview presentation of the APPLICATE Project was given as part of the school programme.

A new climate model supporting multi-resolution meshes in the ocean component has been established at the Alfred Wegener Institute (AWI) in Bremerhaven. The atmospheric component is ECHAM6 with T63L47 setting, while the ocean is simulated by the AWI multi-resolution model FESOM, supporting triangular unstructured meshes. Two multi-century simulations with ECHAM6-FESOM, REF and TRO, document the beneficial role of an increased tropical ocean resolution for ENSO simulations. REF features a tropical ocean resolution of about 1°, TRO employs more than 0.25° in a narrow equatorial band, with resolution gradually decreasing to 1° as in REF. Outside the tropical belt (15°N to 15°S), both meshes are identical. REF and TRO simulate a mean climate comparable to some of the best CMIP5 models. In TRO, however, both the cold tongue SST bias and the western Pacific SST standard deviation bias appear to improve along with the Nino-3 index statistics. Also, advanced ENSO diagnostics including the Nino-3.4 seasonal variance, the annual cycle representation, and its interaction with ENSO tend to improve. The robustness of these improvements is analyzed and their physical explanations are explored.

Berichte aus dem Institut für Meereskunde an der Christian-Albrechts-Universität Kiel No 315

of the presentation given by Thomas Jung at the 2nd EU Climate Modelling "Workshop on Climate Prediction in the Atlantic-Arctic sector" in Bergen (NO), Jointly organised by the Bjerknes Climate Prediction Unit and the EU Modelling Cluster.

The main objective of WP8: Clustering is to collaborate with the European and international community to link with relevant projects in the Arctic and align the project activities with other similar initiatives. One project of high relevance to APPLICATE is the Polar Prediction Project (PPP)1. The PPP was initiated by the World Meteorological Organization (WMO) within the World Weather Research Programme (WWRP) with the aim to promote cooperative international research enabling development of improved weather and environmental prediction services for the polar regions, on time scales from hours to seasonal. The Year of Polar Prediction (YOPP) is the flagship activity within PPP. Planning Workshops on Arctic Observations and on the YOPP Modelling Component were held at ECMWF in Reading, UK, on 5-9 September 2016. Beside APPLICATE, two more H2020 projects were represented at the workshops: INTAROS, Blue-Action. Another important international initiative represented at the workshops: INTAROS, Blue-Action. Another important international initiative represented and discussed at these meetings was MOSAiC.

The main objective of WP8: Clustering is to collaborate with the European and international community to link with relevant projects in the Arctic and align the project activities with other similar initiatives. The project Scientific Advisory Board (AB) plays an important role in clustering activities as it comprises internationally recognised external experts in the fields of dynamics and prediction of weather and climate and representatives of the different stakeholder groups relevant to APPLICATE. The AB will increase the international visibility of APPLICATE and strengthen the international collaboration in weather and climate predictions for the Northern Hemisphere as well as with other European initiatives and projects within this research area.

Presentation given during the "Climate Science 2 Policy" workshop held on 17-18 November 2020, organised by the European Commission EASME.

The aim of APPLICATE is to develop enhanced predictive capacity for weather and climate in the Arctic and beyond, and to determine the influence of Arctic climate change on Northern Hemisphere mid-latitudes, for the benefit of policy makers, businesses and society. In order to place confidence in weather and climate predictions it is essential that weather and climate models are able to represent key processes in the atmosphere, oceans, land and cryosphere. In addition, a key goal of APPLICATE is user engagement and providing relevant information for policy-makers, businesses and society. To address these goals, Deliverable 1.2 aims to develop process-based metrics and diagnostics for the Arctic (Task 1.2.1) and co-develop metrics and diagnostics that are relevant for the stakeholders and users of APPLICATE outputs (Task 1.2.2). To ensure that the evaluation of weather and climate models within APPLICATE is aligned with the wider scientific community, the process-based and user-relevant metrics and diagnostics have been implemented in the open-source ESMValTool software. Metrics and diagnostics were chosen to address gaps in the current capability of ESMValTool and to address APPLICATE User Group requirements. These include ocean and sea ice process- based metrics and diagnostics and user relevant diagnostics and metrics for the shipping, energy and fishing sectors. Through Deliverable 1.2, four APPLICATE partners have further developed their capability to use and develop the ESMValTool software. Developing this capability is essential for the networking effect and wider uptake of ESMValTool at a community level. Achieving Deliverable 1.2 is an important step for APPLICATE as it sits on the critical path for the next tasks in WP1. In particular Deliverable 1.2 will enable the evaluation and assessment of the CMIP5 and CMIP6 climate models in 2018 and 2019 in Task 1.3. The metrics and diagnostics developed in WP1 will also be used to assess the improvement of weather and climate models in WP2. As well as the activity in Deliverable 1.2, additional diagnostics and metrics will be developed later in the project. In particular, metrics and diagnostics used to describe and evaluate the linkages between the Arctic and mid-latitude atmospheric circulation (especially weather and climate extremes) will be developed in APPLICATE WP1 towards the end of 2018. Additionally, the ongoing process of user engagement within APPLICATE WP7 will undoubtedly present new opportunities to co-develop metrics and diagnostics to inform other economic sectors (e.g. strong winds for local communities and the shipping and infrastructure sectors).

The main objective of WP8: Clustering is to collaborate with the European and international community to link with relevant projects in the Arctic and align the project activities with other similar initiatives. One project of high relevance to APPLICATE is the Polar Prediction Project (PPP)1. The PPP was initiated bythe World Meteorological Organization (WMO) within theWorld Weather Research Programme (WWRP) with the aim to promote cooperative international research enabling development of improved weather and environmentalprediction services for the polar regions, on time scales from hours to seasonal. The Year ofPolar Prediction (YOPP) is the flagship activity within PPP. Planning Workshops on Arctic Observations and on the YOPP ModellingComponent were held at ECMWF in Reading, UK, on 5-9 September 2016.Beside APPLICATE, two more H2020 projects were represented at the workshops: INTAROS, Blue-Action. Another important international initiative representedat the workshops: INTAROS, Blue-Action. Another important international initiative representedand discussed at these meetings was MOSAiC. &nbsp

In which direction is the influence larger: from the Arctic to the mid-latitudes or vice versa? To answer this question, CO2 concentrations have been regionally increased in different latitudinal belts, namely in the Arctic, in the northern mid-latitudes, everywhere outside of the Arctic and globally, in a series of 150 year coupled model experiments with the AWI Climate Model. This method is applied to allow a decomposition of the response to increasing CO2 concentrations in different regions. It turns out that CO2 increase applied in the Arctic only is very efficient in heating the Arctic and that the energy largely remains in the Arctic. In the first 30 years after switching on the CO2 forcing some robust atmospheric circulation changes, which are associated with the surface temperature anomalies including local cooling of up to 1°C in parts of North America, are simulated. The synoptic activity is decreased in the mid-latitudes. Further into the simulation, surface temperature and atmospheric circulation anomalies become less robust. When quadrupling the CO2 concentration south of 60°N, the March Arctic sea ice volume is reduced by about two thirds in the 150 years of simulation time. When quadrupling the CO2 concentration between 30 and 60°N, the March Arctic sea ice volume is reduced by around one third, the same amount as if quadrupling CO2 north of 60°N. Both atmospheric and oceanic northward energy transport across 60°N are enhanced by up to 0.1 PW and 0.03 PW, respectively, and winter synoptic activity is increased over the Greenland, Norwegian, Iceland (GIN) seas. To a lesser extent the same happens when the CO2 concentration between 30 and 60°N is only increased to 1.65 times the reference value in order to consider the different size of the forcing areas. The increased northward energy transport, leads to Arctic sea ice reduction, and consequently Arctic amplification is present without Arctic CO2 forcing in all seasons but summer, independent of where the forcing is applied south of 60°N. South of the forcing area, both in the Arctic and northern mid-latitude forcing simulations, the warming is generally limited to less than 0.5°C. In contrast, north of the forcing area in the northern mid-latitude forcing experiments, the warming amounts to generally more than 1°C close to the surface, except for summer. This is a strong indication that the influence of warming outside of the Arctic on the Arctic is substantial, while forcing applied only in the Arctic mainly materializes in a warming Arctic, with relatively small implications for non-Arctic regions.

Presentation made at the PAMIP workshop in Devon, UK, 24th to 27th of June, 2019

The APPLICATE Task 1.2.3 is dedicated to the development of diagnostics/metrics relevant to investigate climate linkages between the Arctic and the mid-latitudes. Here we report the progress made within this task and provide several lists of diagnostics/metrics that can be used by APPLICATE partners and the wider community for weather and climate model evaluation and/or climate change analyses. There are still important gaps in our knowledge regarding the linkages between Arctic changes and mid-latitude variability and changes, both in the atmosphere and in the ocean. Substantial work has been made in Task 1.2.3 to review the literature and select the most appropriate diagnostics for documenting Arctic - mid-latitude linkages. Novel diagnostics have been developed, and several others are still under development. Partners involved in this task already use these diagnostics as metrics for the evaluation of their institutional weather and climate models. The software codes used to calculate the new diagnostics/metrics are now available for APPLICATE partners and very soon available for the wider community. Key diagnostics/metrics will become available in ESMValTool v2.0. The upcoming release of CMIP6 and PAMIP multi-model data constitutes an ideal opportunity (Task 1.3) to sorely test these software codes and to implement well-tested diagnostics/metrics into ESMValTool. The ultimate objectives are (i) to document potential improvements in the representation of mid-latitude dynamics since CMIP5 (including linkages with the Arctic), (ii) to quantify CMIP6 projected changes in the atmospheric circulation, their uncertainties, and the contribution of the Arctic region, and (iii) to narrow model uncertainties in future projections by using the developed metrics as emergent constraints (Task 1.5).

This is a summary of emerging results from the Polar Amplification Model Intercomparison Project, a project under the umbrella of CMIP6, the Coupled Model Intercomparison Project. The focus is on the influence of Arctic sea ice loss on the Northern mid-latitude climate.

Presentation atthe IUP (Institute for Environmental Physics at University of Bremen) - AWI (Alfred Wegener Institute)block seminar on "Polar Amplification" on 30.09.2020 online. The main result of the coordinated atmosphere-only experiments carried out within the Polar Amplification Model Intercomparison Project (PAMIP) is that regional details of an atmosphericresponse to declined Arctic sea ice are not robust. Also very high horizontal and vertical resolutions do not change this conclusion. Differences between 100 ensemble member packs within a 300 member ensemble are as large as differences between different resolutions.

Presentation given at the 2020 AAAS Annual Meeting in Seattle, Washington, during the session "The Future of Earth’s Climate: A World of Extremes?" organised by the European Commission EASME.

Presentation at the IUP (Institute for Environmental Physics at University of Bremen) - AWI (Alfred Wegener Institute) block seminar on "Polar Amplification" on 30.09.2020 online. The main result of the coordinated atmosphere-only experiments carried out within the Polar Amplification Model Intercomparison Project (PAMIP) is that regional details of an atmospheric response to declined Arctic sea ice are not robust. Also very high horizontal and vertical resolutions do not change this conclusion. Differences between 100 ensemble member packs within a 300 member ensemble are as large as differences between different resolutions.

of the presentation given by Thomas Jung at the 2nd EU Climate Modelling "Workshop on Climate Prediction in the Atlantic-Arctic sector" in Bergen (NO), Jointly organised by the Bjerknes Climate Prediction Unit and the EU Modelling Cluster.

The aim of APPLICATE isto develop enhanced predictive capacity for weather and climate in the Arctic and beyond, and to determine the influence of Arctic climate change on Northern Hemisphere mid-latitudes, for the benefit of policy makers, businesses and society.In order to place confidence in weather and climate predictions it is essential that weather and climate models are able to represent key processes in the atmosphere, oceans, land and cryosphere. In addition, a key goal of APPLICATE is user engagement and providing relevant information for policy-makers, businesses and society. To address these goals, Deliverable 1.2 aims to develop process-based metrics and diagnostics for the Arctic (Task 1.2.1) and co-develop metrics and diagnostics that are relevant for the stakeholders and users of APPLICATE outputs (Task 1.2.2). To ensure that the evaluation of weather and climate models within APPLICATE is aligned with the wider scientific community, the process-based and user-relevant metrics and diagnostics have been implemented in the open-source ESMValTool software. Metrics and diagnostics were chosen to address gaps in the current capability of ESMValTool and to address APPLICATE User Group requirements. These include ocean and sea ice process- based metrics and diagnostics and user relevant diagnostics and metrics for the shipping, energy and fishing sectors. Through Deliverable 1.2, four APPLICATE partners have further developed their capability to use and develop the ESMValTool software. Developing this capability is essential for the networking effect and wider uptake of ESMValTool at a community level. Achieving Deliverable 1.2 is an important step for APPLICATE as it sits on the critical path for the next tasks in WP1. In particular Deliverable 1.2 will enable the evaluation and assessment of the CMIP5 and CMIP6 climate models in 2018 and 2019 in Task 1.3. The metrics and diagnostics developed in WP1 will also be used to assess the improvement of weather and climate models in WP2. As well as the activity in Deliverable 1.2, additional diagnostics and metrics will be developed later in the project. In particular, metrics and diagnostics used to describe and evaluate the linkages between the Arctic and mid-latitude atmospheric circulation (especially weather and climate extremes) will be developed in APPLICATE WP1 towards the end of 2018. Additionally, the ongoing process of user engagement within APPLICATE WP7 will undoubtedly present new opportunities to co-develop metrics and diagnostics to inform other economic sectors (e.g. strong winds for local communities and the shipping and infrastructure sectors).

This is a summary of emerging results from the Polar Amplification Model Intercomparison Project, a project under the umbrella of CMIP6, the Coupled Model Intercomparison Project. The focus is on the influence of Arctic sea ice loss on the Northern mid-latitude climate.

WP7: user engagement, dissemination and training, aims at increasing awareness of the impact of Arctic changes on weather and climate of the Northern Hemisphere by developing relevant forms of communication to spread the project results and maximise the impact and exposure of the science produced to end-users, policy makers and the public at large. To achieve this objective, WP7 has from the start of the project, developed several outreach materials as per deliverables D7.5 and D7.6. The WP will continuously update and add as relevant outreach materials targeted at various specific audiences that will be disseminated by the projects outreach team and its communication channels such as the project website and social media channels, by project partners on the occasion of seminars, conferences and at appropriate public exhibitions. Several dissemination materials have been developed as per deliverables D7.5 and D.7.6 and are maintained and available to stakeholders, the public and project partners to use through the project website and / or its internal document management system. These include: the project logo, the project website, social media channels (Facebook and Twitter), a project flyer/brochure, a rollup poster and an introductory presentation of the project, project poster,a newsletter and frostbytes videos. New additions since deliverable D7.6 in November 2017 include: - The project logo has been updated. - The project website has been updated. - Project publications library has been implemented. - Project flyer has been updated with projects highlights todate. - A project poster and template for use at conferences updated with project highlights todate. - Further important additions to the the Year of Polar Prediction (YOPP) blog, as a result of the APPLICATE partnership. - The third organised webinar in cooperation with the Association for Polar Early Career Scientists (APECS) was given in early January 2018 by Doug Smith who talked about atmosphere-ocean interactions (WP3). - Form for collecting information on partners outreach activites has been initiated. - First newsletter published, June 2018. - You Tube channel with project related video material established - Project promotional video produced, October 2018 and first view during the Arctic Circle event. - Frostbite videos based on the summer training school produced and avialable on the project website and the project You Tube channel. Further dissemination materials will continuously be developed as needed throughout the project lifetime, tailored to specific end-user groups to disseminate project results, inform and impact stakeholders and policymakers and engage with end-users. Some foreseen materials are: a series of fact sheets, a series of policy briefs in cooperation with the EU project Blue-Action and the EU Arctic Cluster and an overview video.

Simulating Arctic Ocean mesoscale eddies in ocean circulation models presents a great challenge because of their small size. This study employs an unstructured-mesh ocean-sea ice model to conduct a decadal-scale global simulation with a 1-km Arctic. It provides a basinwide overview of Arctic eddy energetics. Increasing model resolution from 4 to 1 km increases Arctic eddy kinetic energy (EKE) and total kinetic energy (TKE) by about 40% and 15%, respectively. EKE is the highest along main currents over topography slopes, where strong conversion from available potential energy to EKE takes place. It is high in halocline with a maximum typically centered in the depth range of 70–110 m, and in the Atlantic Water layer of the Eurasian Basin as well. The seasonal variability of EKE along the continental slopes of southern Canada and eastern Eurasian basins is similar, stronger in fall and weaker in spring.

Proceedings of the 5th International Climate Change Adaptation Conference, Cape Town, South Africa, 18 -21 June 2018

Presentation given during the International Glaciological Society Sea Ice Symposium in Winnipeg, CA, on August 23rd, 2019.

Having a thorough model assessment capacity is critical for the APPLICATE project in order to establish the ability of existing models in simulating Arctic weather and climate along with Arctic-midlatitude interactions, provide guidance for APPLICATE model development activities, and to measure the impact and hence success of the APPLICATE project. This Model Assessment Plan outlines the project’s model assessment strategy, making extensive use of the concept of metrics and diagnostics, and utilizing comprehensive sets of observational data. In this context the Plan focuses on evaluating the model’s ability to represent critical Arctic processes, linkages between the Arctic and mid-latitude weather and climate, and user-relevant parameters. The plan also outlines how the metrics and diagnostics will feed into ESMValTool, a tool used by the international research community for evaluating climate models. Importantly, the Plan also considers the evaluation of numerical weather prediction (NWP) models and seasonal forecasting systems. This assessment will not only provide the basis for enhancing prediction capacity; it will also lead to insight into the origin of model error and thus contributes to providing guidance for the design of the observing system. Regional Arctic heat budget analyses will be used to assess the ability of models to reproduce key processes in the Arctic and to identify important feedbacks and processes affecting Arctic climate variability and sea ice change. Towards the end of the project, the potential will be explored for the heat budget and process- based metrics developed within APPLICATE to provide observation-based constraints on the climate models to reduce uncertainty in future projections. To facilitate effective management of WP1 timelines are given for the different and critical relationships to other WPs are outlined. The APPLICATE Model Assessment Plan is a “living document” that will be updated regularly. This version 2 (November 2018) is to be considered an update of the original deliverable (May 2017) and includes the progress achieved in the first half of the project and the outcome of the discussion following the first project review (September 2018).

The main objective of WP8: Clustering is to collaborate with the European and international community to link with relevant projects in the Arctic and align the project activities with other similar initiatives. The project Scientific Advisory Board (AB) plays an important role in clustering activities as it comprises internationally recognised external experts in the fields of dynamics and prediction of weather and climate and representatives of the different stakeholder groups relevant to APPLICATE. The AB will increase the international visibility of APPLICATE and strengthen the international collaboration in weather and climate predictions for the Northern Hemisphere as well as with other European initiatives and projects within this research area.

Coupled climate simulations were performed with four different combinations of atmospheric and oceanic horizontal resolutions in our mixed-resolution experiments (OCE_LR+T63, OCE_LR+T127, OCE_HR+T63, OCE_HR+T127). We investigated the effect of horizontal grid resolution on volume and heat transports through the Arctic gateways and found that the difference in ocean resolution accounts for most of the differences in simulated present-day and future volume and heat transports through the gateways - most prominently in the Atlantic sector through the Fram Strait and at the Barents Sea entrance. In Fram Strait, with the lower ocean resolution a higher increase in net outflow is predicted for the end of the 21st century than with higher ocean resolution. This is mainly driven by a predicted decrease in inflow through Fram Strait. For the Barents Sea entrance the net inflow is predicted to increase towards the end of the first century. This predicted increase is also higher with lower resolution. At the Barents Sea entrance all simulations predict a considerable increase of heat transport into the Arctic. In accordance with the predicted higher volume transport into the Barents Sea in the lower resolution ocean, the heat transport is also significantly higher with lower ocean resolution. Between low and high atmospheric resolution, the predicted end-century heat transport into the Barents Sea is higher with higher atmospheric resolution on both ocean grids.

Presentation given during the European Polar Science Week on October 28th, 2020.

Ocean heat transport through the Barents Sea Opening (BSO) has strong impacts on the Barents Sea ice extent and the climate. In this paper we quantified the contributions from different atmospheric forcing components to the trend and interannual variability of the BSO heat transport. Ocean-ice model simulations were conducted in which the interannual variation of atmospheric forcing was maintained only in or outside the Arctic in two different simulations. The sum of their BSO heat transport anomalies reasonably replicated the trend and variability from a hindcast simulation. The upward trend of the BSO heat transport mainly stems from the increasing ocean temperature in the subpolar North Atlantic. For the interannual variability, the local wind and upstream forcing are similarly important. The location of the Atlantic Water boundary current in the Nordic Seas, influenced by the cyclonic atmospheric circulation, is crucial in determining part of the BSO inflow variability.

Presentation of an overview of the APPLICATE Project's purposes and objectives in occasion of the General Assembly of the H2020 fellow Arctic Cluster Project EU-PolarNet. The meeting took place on Monday, April 3rd 2017 in Prague (Czech Republic).

Presentation on the APPLICATE energy case study in the webinar 'Climate services for energy: sharing knowledge through case studies' organised by the European H2020 project Climateurope

Presentation given during the European Polar Science Week on October 28th, 2020.

Having a thorough model assessment capacity is critical for the APPLICATE project in order to establish the ability of existing models in simulating Arctic weather and climate along with Arctic-midlatitude interactions, provide guidance for APPLICATE model development activities, and to measure the impact and hence success of the APPLICATE project. This Model Assessment Plan outlines the project’s model assessment strategy, making extensive use of the concept of metrics and diagnostics, and utilizing comprehensive sets of observational data. In this context the Plan focuses on evaluating the model’s ability to represent critical Arctic processes, linkages between the Arctic and mid-latitude weather and climate, and user-relevant parameters. The plan also outlines how the metrics and diagnostics will feed into the Earth System Model Evaluation Tool (ESMValTool), a tool used by the international research community for evaluating climate models. Importantly, the Plan also considers the evaluation of numerical weather prediction (NWP) models and seasonal forecasting systems. This assessment will not only provide the basis for enhancing prediction capacity; it will also lead to insight into the origin of model error and contributes to providing guidance for the design of the observing system. Regional Arctic heat budget analyses will be used to assess the ability of models to reproduce key processes in the Arctic and to identify important feedbacks and processes affecting Arctic climate variability and sea ice change. Towards the end of the project, the potential will be explored for the heat budget and process-based metrics developed within APPLICATE to provide observation-based constraints on the climate models to reduce uncertainty in future projections. To facilitate effective management of WP1 timelines are given for the different and critical relationships to other WPs are outlined. The APPLICATE Model Assessment Plan is a “living document” that will be updated regularly (approximately every 6 months).

Having a thorough model assessment capacity is critical for the APPLICATE project in order to establish the ability of existing models in simulating Arctic weather and climate along with Arctic-midlatitude interactions, provide guidance for APPLICATE model development activities, and to measure the impact and hence success of the APPLICATE project. This Model Assessment Plan outlines the project’s model assessment strategy, making extensive use of the concept of metrics and diagnostics, and utilizing comprehensive sets of observational data. In this context the Plan focuses on evaluating the model’s ability to represent critical Arctic processes, linkages between the Arctic and mid-latitude weather and climate, and user-relevant parameters. The plan also outlines how the metrics and diagnostics will feed into ESMValTool, a tool used by the international research community for evaluating climate models. Importantly, the Plan also considers the evaluation of numerical weather prediction (NWP) models and seasonal forecasting systems. This assessment will not only provide the basis for enhancing prediction capacity; it will also lead to insight into the origin of model error and thus contributes to providing guidance for the design of the observing system. Regional Arctic heat budget analyses will be used to assess the ability of models to reproduce key processes in the Arctic and to identify important feedbacks and processes affecting Arctic climate variability and sea ice change. Towards the end of the project, the potential will be explored for the heat budget and process- based metrics developed within APPLICATE to provide observation-based constraints on the climate models to reduce uncertainty in future projections. To facilitate effective management of WP1 timelines are given for the different and critical relationships to other WPs are outlined. The APPLICATE Model Assessment Plan is a “living document” that will be updated regularly. This version 2 (November 2018) is to be considered an update of the original deliverable (May 2017) and includes the progress achieved in the first half of the project and the outcome of the discussion following the first project review (September 2018).

Relaxation experiments with the atmosphere model from European Centre for Medium‐range Weather Forecasts are analyzed to understand influence of lower latitudes (south of about 52 °N) on climate variability and change over the Arctic region. Interannual variability of the Arctic troposphere is impacted strongly by both the tropics and the midlatitudes. In general, the link in winter is stronger than that in summer. Furthermore, the tropics and midlatitudes have different preferred pathways by which they influence the Arctic. Trend analysis suggests that winter surface warming trends over the Arctic are driven strongly by the local sea ice‐atmospheric interaction. Warming at higher altitudes is strongly tied to remote non‐Arctic drivers, with some local amplification. Summer warming trends in northeastern Canada and Greenland are driven strongly by sea surface temperature/sea ice changes and partly by the tropics. The summer warming in northern Europe and western Russia is more strongly driven by the midlatitudes.

The US CLIVAR Working Group on Arctic Change and Possible Influence on Mid-Latitude Climate and Weather has been established to further the understanding of the coupling between Arctic variability and mid-latitude climate and weather. Its aims relate strongly with those of APPLICATE WP3, i.e., to advance our understanding of the mechanisms by which mid-latitude weather and climate cold respond to Arctic climate change. The Working Group convened an international workshop at Georgetown University in Washington, DC, on 1-3 February 2017, to assemble experts across the fields of atmosphere, ocean, and cryosphere sciences to assess the rapidly evolving state of understanding and to identify consensus on knowledge and gaps in research, and to develop specific actions to accelerate progress within the research community. APPLICATE coordinator Thomas Jung (AWI) and WP3-leader Doug Smith (MetOffice) participated in the workshop on behalf of the APPLICATE Consortium to strengthen the link with the working group and to gather recommendations for the WP3 numerical experimentation plan. The workshop found that our understanding of Arctic amplification (AA) is incomplete, Arctic- midlatitude linkages aren’t yet well understood, and observations and analysis are currently incomplete. Recommendations for the modelling community included the creation of a modelling task force to coordinate MIP experiments drawing from the initial planning and discussions of the US CLIVAR Working Group and planned modelling element of the European Horizon 2020 projects (APPLICATE, Blue Action, and PRIMAVERA).

The main objective of the APPLICATE project is to develop enhanced predictive capacity for weather and climate in the Arctic and beyond, and to determine the influence of Arctic climate change on the Northern Hemisphere. To produce usable and trustworthy predictive information for decision making, APPLICATE will actively engage with users, including policy makers, businesses and society within and outside the EU. Only by effectively exchanging information with stakeholders and co-developing knowledge, can we assure the stakeholder-relevance of the project results, which can then enhance their capacity to adapt to long-term climate change. The proactive dialogue with users will be performed using modern and interactive user engagement mechanisms that will be developed and maintained throughout the project. This updated plan describes already applied engagement approaches and activities, as well as those planned for the rest of the project. It provides a detailed description of the three main user categories defined by the project – key, primary and secondary. It builds around three main mechanisms of user engagement to be applied in the project: i) User Group involvement ii) Participation in meetings and organization of workshops, iii) Case studies development iv) User blog and interviews. In order to maximize the projects impact in a meaningful, direct and measurable way, specific users have been and will be targeted and involved through the projects User-Group. Further identification of project relevant users, to be consulted and impacted through case-studies and organised events, will be on going. Project impact on identified specific users will be measured through the stakeholder engagement and collected stakeholder feedback. In addition, different communication channels that are also being developed and maintained as a part of the project, including the project website, social media channels and project dissemination material, will enhance information exchange and knowledge transfer, presenting the first step towards user engagement and reaching a broad and diverse group of users.

Keynote presentation at the EMS General Assembly in Lyngby, Denmark, 9th to 13th of September, 2019.

Proceedings of the 5th International Climate Change Adaptation Conference, Cape Town, South Africa, 18 -21 June 2018

Having a thorough model assessment capacity is critical for the APPLICATE project in order to establish the ability of existing models in simulating Arctic weather and climate along with Arctic-midlatitude interactions, provide guidance for APPLICATE model development activities, and to measure the impact and hence success of the APPLICATE project. This Model Assessment Plan outlines the project’s model assessment strategy, making extensive use of the concept of metrics and diagnostics, and utilizing comprehensive sets of observational data. In this context the Plan focuses on evaluating the model’s ability to represent critical Arctic processes, linkages between the Arctic and mid-latitude weather and climate, and user-relevant parameters. The plan also outlines how the metrics and diagnostics will feed into the Earth System Model Evaluation Tool (ESMValTool), a tool used by the international research community for evaluating climate models. Importantly, the Plan also considers the evaluation of numerical weather prediction (NWP) models and seasonal forecasting systems. This assessment will not only provide the basis for enhancing prediction capacity; it will also lead to insight into the origin of model error and contributes to providing guidance for the design of the observing system. Regional Arctic heat budget analyses will be used to assess the ability of models to reproduce key processes in the Arctic and to identify important feedbacks and processes affecting Arctic climate variability and sea ice change. Towards the end of the project, the potential will be explored for the heat budget and process-based metrics developed within APPLICATE to provide observation-based constraints on the climate models to reduce uncertainty in future projections. To facilitate effective management of WP1 timelines are given for the different and critical relationships to other WPs are outlined. The APPLICATE Model Assessment Plan is a “living document” that will be updated regularly (approximately every 6 months).

This poster has been presented at the General Assembly of the EU project APPLICATE which has taken place in Louvain-la-Neuve, Belgium, from the 20th to 23rd of January, 2020. It is a summary of the paper by the same authors (Semmler et al., 2020: Quantifying two-way influences between the Arctic and mid-latitudes through regionally increased CO2 concentrations in coupled climate simulations, doi: 10.1007/s00382-020-05171-z). One of the main conclusions is: Arctic CO2 forcing shows limited influence on extra-Arctic regions, extra-Arctic CO2 forcing shows strong influence on Arctic including substantial sea ice melting leading to Arctic Amplification.

Polar amplification – the phenomenon where external radiative forcing produces a larger change in surface temperature at high latitudes than the global average – is a key aspect of anthropogenic climate change, but its causes and consequences are not fully understood. The Polar Amplification Model Intercomparison Project (PAMIP) contribution to the sixth Coupled Model Intercomparison Project (CMIP6; Eyring et al., 2016) seeks to improve our understanding of this phenomenon through a coordinated set of numerical model experiments documented here. In particular, PAMIP will address the following primary questions: (1)what are the relative roles of local sea ice and remote sea surface temperature changes in driving polar amplification? (2)How does the global climate system respond to changes in Arctic and Antarctic sea ice? These issues will be addressed with multi-model simulations that are forced with different combinations of sea ice and/or sea surface temperatures representing present-day, pre-industrial and future conditions. The use of three time periods allows the signals of interest to be diagnosed in multiple ways. Lower-priority tier experiments are proposed to investigate additional aspects and provide further understanding of the physical processes. These experiments will address the following specific questions: what role does ocean–atmosphere coupling play in the response to sea ice? How and why does the atmospheric response to Arctic sea ice depend on the pattern of sea ice forcing? How and why does the atmospheric response to Arctic sea ice depend on the model background state? What have been the roles of local sea ice and remote sea surface temperature in polar amplification, and the response to sea ice, over the recent period since 1979? How does the response to sea ice evolve on decadal and longer timescales? A key goal of PAMIP is to determine the real-world situation using imperfect climate models. Although the experiments proposed here form a coordinated set, we anticipate a large spread across models. However, this spread will be exploited by seeking “emergent constraints” in which model uncertainty may be reduced by using an observable quantity that physically explains the intermodel spread. In summary, PAMIP will improve our understanding of the physical processes that drive polar amplification and its global climate impacts, thereby reducing the uncertainties in future projections and predictions of climate change and variability.

In which direction is the influence larger: from the Arctic to the mid-latitudes or vice versa? To answer this question, CO2 concentrations have been regionally increased in different latitudinal belts, namely in the Arctic, in the northern mid-latitudes, everywhere outside of the Arctic and globally, in a series of 150 year coupled model experiments with the AWI Climate Model. This method is applied to allow a decomposition of the response to increasing CO2 concentrations in different regions. It turns out that CO2 increase applied in the Arctic only is very efficient in heating the Arctic and that the energy largely remains in the Arctic. In the first 30 years after switching on the CO2 forcing some robust atmospheric circulation changes, which are associated with the surface temperature anomalies including local cooling of up to 1°C in parts of North America, are simulated. The synoptic activity is decreased in the mid-latitudes. Further into the simulation, surface temperature and atmospheric circulation anomalies become less robust. When quadrupling the CO2 concentration south of 60°N, the March Arctic sea ice volume is reduced by about two thirds in the 150 years of simulation time. When quadrupling the CO2 concentration between 30 and 60°N, the March Arctic sea ice volume is reduced by around one third, the same amount as if quadrupling CO2 north of 60°N. Both atmospheric and oceanic northward energy transport across 60°N are enhanced by up to 0.1 PW and 0.03 PW, respectively, and winter synoptic activity is increased over the Greenland, Norwegian, Iceland (GIN) seas. To a lesser extent the same happens when the CO2 concentration between 30 and 60°N is only increased to 1.65 times the reference value in order to consider the different size of the forcing areas. The increased northward energy transport, leads to Arctic sea ice reduction, and consequently Arctic amplification is present without Arctic CO2 forcing in all seasons but summer, independent of where the forcing is applied south of 60°N. South of the forcing area, both in the Arctic and northern mid-latitude forcing simulations, the warming is generally limited to less than 0.5°C. In contrast, north of the forcing area in the northern mid-latitude forcing experiments, the warming amounts to generally more than 1°C close to the surface, except for summer. This is a strong indication that the influence of warming outside of the Arctic on the Arctic is substantial, while forcing applied only in the Arctic mainly materializes in a warming Arctic, with relatively small implications for non-Arctic regions.

Relaxation experiments with the atmosphere model from European Centre for Medium‐range Weather Forecasts are analyzed to understand influence of lower latitudes (south of about 52 °N) on climate variability and change over the Arctic region. Interannual variability of the Arctic troposphere is impacted strongly by both the tropics and the midlatitudes. In general, the link in winter is stronger than that in summer. Furthermore, the tropics and midlatitudes have different preferred pathways by which they influence the Arctic. Trend analysis suggests that winter surface warming trends over the Arctic are driven strongly by the local sea ice‐atmospheric interaction. Warming at higher altitudes is strongly tied to remote non‐Arctic drivers, with some local amplification. Summer warming trends in northeastern Canada and Greenland are driven strongly by sea surface temperature/sea ice changes and partly by the tropics. The summer warming in northern Europe and western Russia is more strongly driven by the midlatitudes.

The main objective of the APPLICATE project is to develop enhanced predictive capacity for weather and climate in the Arctic and beyond, and to determine the influence of Arctic climate change on the Northern Hemisphere. To produce usable and trustworthy predictive information for decision making, APPLICATE will actively engage with users, including policy makers, businesses and society within and outside the EU. Only by effectively exchanging information with stakeholders and co-developing knowledge, can we assure the stakeholder-relevance of the project results, which can then enhance their capacity to adapt to long-term climate change. The proactive dialogue with users will be performed using modern and interactive user engagement mechanisms that will be developed and maintained throughout the project. This updated plan describes already applied engagement approaches and activities, as well as those planned for the rest of the project. It provides a detailed description of the three main user categories defined by the project – key, primary and secondary. It builds around three main mechanisms of user engagement to be applied in the project: i) User Group involvement ii) Participation in meetings and organization of workshops, iii) Case studies development iv) User blog and interviews. In order to maximize the projects impact in a meaningful, direct and measurable way, specific users have been and will be targeted and involved through the projects User-Group. Further identification of project relevant users, to be consulted and impacted through case-studies and organised events, will be on going. Project impact on identified specific users will be measured through the stakeholder engagement and collected stakeholder feedback. In addition, different communication channels that are also being developed and maintained as a part of the project, including the project website, social media channels and project dissemination material, will enhance information exchange and knowledge transfer, presenting the first step towards user engagement and reaching a broad and diverse group of users.

WP7: user engagement, dissemination and training, aims at increasing awareness of the impact of Arctic changes on weather and climate of the Northern Hemisphere by developing relevant forms of communication to spread the project results and maximise the impact and exposure of the science produced to end-users, policy makers and the public at large. To achieve this objective, WP7 has from the start of the project, developed several outreach materials as per deliverables D7.5 and D7.6. The WP will continuously update and add as relevant outreach materials targeted at various specific audiences that will be disseminated by the projects outreach team and its communication channels such as the project website and social media channels, by project partners on the occasion of seminars, conferences and at appropriate public exhibitions. Several dissemination materials have been developed as per deliverables D7.5 and D.7.6 and are maintained and available to stakeholders, the public and project partners to use through the project website and / or its internal document management system. These include: the project logo, the project website, social media channels (Facebook and Twitter), a project flyer/brochure, a rollup poster and an introductory presentation of the project, project poster,a newsletter and frostbytes videos. New additions since deliverable D7.6 in November 2017 include: - The project logo has been updated. - The project website has been updated. - Project publications library has been implemented. - Project flyer has been updated with projects highlights todate. - A project poster and template for use at conferences updated with project highlights todate. - Further important additions to the the Year of Polar Prediction (YOPP) blog, as a result of the APPLICATE partnership. - The third organised webinar in cooperation with the Association for Polar Early Career Scientists (APECS) was given in early January 2018 by Doug Smith who talked about atmosphere-ocean interactions (WP3). - Form for collecting information on partners outreach activites has been initiated. - First newsletter published, June 2018. - You Tube channel with project related video material established - Project promotional video produced, October 2018 and first view during the Arctic Circle event. - Frostbite videos based on the summer training school produced and avialable on the project website and the project You Tube channel. Further dissemination materials will continuously be developed as needed throughout the project lifetime, tailored to specific end-user groups to disseminate project results, inform and impact stakeholders and policymakers and engage with end-users. Some foreseen materials are: a series of fact sheets, a series of policy briefs in cooperation with the EU project Blue-Action and the EU Arctic Cluster and an overview video.

Keynote presentation at the EMS General Assembly in Lyngby, Denmark, 9th to 13th of September, 2019.

The session “Ocean and Polar Processes” at the Climate Science2Policy Workshop on 17 November 2020 was organised by the H2020 projects Blue-Action, APPLICATE, SO-CHIC and NUNATARYUK. A summary of policy recommendations and of the research gaps is presented in the slides uploaded here.

Understanding the influence of the Arctic troposphere on the climate at midlatitudes is critical for projecting the impacts of ongoing and anticipated Arctic changes such as Arctic amplification and rapid sea ice decline over the Northern Hemisphere. In this study, we analyze a suite of atmospheric model experiments, with and without atmospheric relaxation toward reanalysis data, to study the impacts of the Arctic troposphere on the midlatitude atmospheric circulation and climate variability. The Arctic troposphere is found to strongly impact the interannual variability of the atmospheric circulation and temperature over the midlatitude continents. The major mechanisms for the impacts of Arctic troposphere include the modulation of the large-scale atmospheric circulation, the associated heat transport over the continents, and the impacts on synoptic variations in the North Atlantic-European sector. The impact of the Arctic troposphere on the intensity of the Siberian High is an important factor for how the Arctic can influence temperature variability in south Siberia and East Asia. The trends in the Arctic troposphere in recent decades are closely linked to the recent winter cooling in Northern Eurasia. These recent cooling trends are not driven by the trends in sea surface temperature/sea ice, tropical atmosphere, and the stratosphere. It is argued that the temperature trend pattern of warm Arctic-cold Eurasia is a manifestation of two possibly independent phenomena and the cooling trend is contributed to by the Arctic troposphere through impacting the large-scale atmospheric circulation, the atmospheric blocking frequency, and the intensity of the Siberian High.

Presentation given at the 2020 AAAS Annual Meeting in Seattle, Washington, during the session "The Future of Earth’s Climate: A World of Extremes?" organised by the European Commission EASME.

Coupled climate simulations were performed with four different combinations of atmospheric and oceanic horizontal resolutions in our mixed-resolution experiments (OCE_LR+T63, OCE_LR+T127, OCE_HR+T63, OCE_HR+T127). We investigated the effect of horizontal grid resolution on volume and heat transports through the Arctic gateways and found that the difference in ocean resolution accounts for most of the differences in simulated present-day and future volume and heat transports through the gateways - most prominently in the Atlantic sector through the Fram Strait and at the Barents Sea entrance. In Fram Strait, with the lower ocean resolution a higher increase in net outflow is predicted for the end of the 21st century than with higher ocean resolution. This is mainly driven by a predicted decrease in inflow through Fram Strait. For the Barents Sea entrance the net inflow is predicted to increase towards the end of the first century. This predicted increase is also higher with lower resolution. At the Barents Sea entrance all simulations predict a considerable increase of heat transport into the Arctic. In accordance with the predicted higher volume transport into the Barents Sea in the lower resolution ocean, the heat transport is also significantly higher with lower ocean resolution. Between low and high atmospheric resolution, the predicted end-century heat transport into the Barents Sea is higher with higher atmospheric resolution on both ocean grids.