1. We will investigate inter-regional and inter-basin linkages on sub-seasonal to interannual time scales, achieved mainly through atmospheric teleconnections. At present, the role of air-sea interactions among different latitude belts in the Atlantic and Pacific, and of stratosphere -troposphere coupling in these linkages has not been clarified. We will explore those linkages in existing observational and reanalysis data sets and through sets of coordinated multi-model experiments  with  state-of-the-art  atmospheric  general  circulation  models  (AGCMs),  where possible remote climate impacts of daily distributions of observed SST and sea ice (1980-2015) in certain key regions (e.g. Arctic, North Atlantic, North Pacific, Tropics) will be assessed. We will further perform experiments with suppressed stratospheric pathways. We will also examine the interaction between the Madden Julian Oscillation and high-latitude weather patterns.

2. We will examine Inter-regional linkages on decadal-scale time scales in existing CMIP5 historical simulations and include oceanic teleconnections through sets of coordinated multi-model partially coupled climate model and pacemaker7 experiments, covering the entire 20th century. Partial coupled model simulations, which are forced by observed wind stress or SST anomalies, maintain a more consistent thermodynamic coupling compared to SST-driven AGCM experiments. To investigate the resolution-dependence of the identified linkages, we will make use  of  high-resolution  climate  model  (~25km  resolution)  simulations  (1950-2050)  to performed within the Horizon 2020 PRIMAVERA project

3. Based on the results of part 1 and 2, we will assess the predictability of societally relevant climate variations and extreme events. Examples are the recent period with fast Arctic sea loss, periods with enhanced/reduced African and Asian Monsoon activity or extreme Eurasian summer and winter temperatures. We will explore the limits of predictability related to the identified processes and linkages by analysing existing multi-model repositories of seasonal-to-decadal hindcast simulations (CMIP5/CMIP6, SPECS, MiKlip, S2S). Additional pacemaker type prediction  experiments  will  be  performed  to  further  explore  the  potential  to  enhance predictability in certain cases such as sharp climatic shifts or transitions.

Cooperative approach

53             Our proposed research requires a comprehensive approach through international collaboration.

54             The usage of already existing simulations in combination with new dedicated experiments

55             assures an optimal use of the requested funding. The coordinated multi-model approach is crucial

56             for assessing the robustness of the results and quantifying uncertainty, but cannot be achieved on

57             a  national  level.  The  NordForsk  GREENICE8   project  is  performing  such  a  multi-AGCM

58             ensemble focusing on the role of sea ice changes, but is limited to Scandinavian partners. We

59             will extend this initiative to include other AGCMs from German, UK, Chinese and Japanese

60             partners, and to perform additional experiments targeted at Arctic-lower latitudes linkages.

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62             Our consortium brings together expertise in North Atlantic/European, North Pacific/East Asian,

63             Arctic and Tropical climate, as well as in atmosphere and ocean dynamics, and teleconnections.

64             The consortium has extensive expertise in climate variability and response, and seasonal-to-

65             decadal predictability studies. This complementary expertise not only ensures that the scientific

66             questions will be answered in a comprehensive manner, but also most efficient use of the

67             resources at the different partner institutions as well as enhanced cooperation among institutions

68             inside Europe and Asia. By combining project meetings with other international meetings and

69             virtual project meetings, we will minimize travel cost and reduce the carbon footprint of this

70             project.

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72             Societal benefits

73             Societies are vulnerable to weather and climate extremes by setting agriculture and infrastructure

74             at risk, increasing the risk for forest fires or causing health problems. Systematic analysis of

75             inter-regional  linkages  between  Arctic,  mid-latitudes  and  Tropics  will  lead  to  a  better

76             understanding of extreme events such as monsoon breaks and intensifications, Eurasian mid-

77             latitude cold spells and heat waves or rapid declines in Arctic sea ice. Identifying key regions

78             driving decadal-scale variations can lead to more reliable decadal predictions, which in turn can

79             improve disaster prevention and mitigation strategies, especially in densely populated areas.

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81             The climate processes and time scale considered here are of high relevance for climate services

82             and Future Earth-related research activities. Partners of the consortium have close connections to

83             climate service centres and stakeholders within current projects (e.g. NordForsk GREENICE,

84             BMBF MiKlip, FP7 EUPORIAS, FP7 SPECS, GRENE-ArCS, S2S). Key results of this project

85             will be disseminated through a project website, fact sheets, participation in users’ workshops,

86             and  sharing  the  model  data.  The  poor  anticipation  of  the  recent  global  warming  hiatus

87             highlighted the existing communication gap9  among climate scientists, stakeholders and the

88             general public. The better attribution of regional weather and climate fluctuations to large-scale

89             decadal-scale climate variations will help in this regard.