In recent years, the Northern Hemisphere midlatitudes have suffered from severe winters like the extreme 2012/13 winter in the eastern United States. These cold spells were linked to a meandering upper-tropospheric jet stream pattern and a negative Arctic Oscillation index (AO). However, the nature of the drivers behind these circulation patterns remains controversial. Various studies have proposed different mechanisms related to changes in the Arctic, most of them related to a reduction in sea ice concentrations or increasing Eurasian snow cover.
Here, a novel type of time series analysis, called causal effect networks (CEN), based on graphical models is introduced to assess causal relationships and their time delays between different processes. The effect of different Arctic actors on winter circulation on weekly to monthly time scales is studied, and robust network patterns are found. Barents and Kara sea ice concentrations are detected to be important external drivers of the midlatitude circulation, influencing winter AO via tropospheric mechanisms and through processes involving the stratosphere. Eurasia snow cover is also detected to have a causal effect on sea level pressure in Asia, but its exact role on AO remains unclear. The CEN approach presented in this study overcomes some difficulties in interpreting correlation analyses, complements model experiments for testing hypotheses involving teleconnections, and can be used to assess their validity. The findings confirm that sea ice concentrations in autumn in the Barents and Kara Seas are an important driver of winter circulation in the midlatitudes.
General news | 2018-03-19
In 2017, we surpassed one thousand published articles in peer-reviewed journals and we hosted the fourth international conference on resilience and sustainability science. Another year to be proud of, we think
Research news | 2018-03-14
Amid an increase in megacities, changes in ecosystems far away can affect local access to freshwater
Research news | 2018-03-12
Ten essentials for guiding action-oriented research on energy transformation and climate change
Research news | 2018-03-09
To celebrate International Women’s Day, we have been highlighting some of our women researchers at the centre. In our final profile this week, we showcase associate professor Beatrice Crona, whose work spans from small-scale fisheries governance to global drivers of change.
Research news | 2018-03-08
To celebrate International Women’s Day, we are highlighting some of our women researchers. We would now like to showcase Jennifer Hinton, a PhD candidate studying the social dynamics of a sustainable biophysical resource economy
Research news | 2018-03-08
New method to map livelihood benefits of ecosystem services for guiding future land use decisions in the Sahel