Does the Arctic sea-ice loss have an impact on the winter weather patterns in Europe? (EuropeWeather)

The rise in near-surface air temperatures in the Arctic has been almost twice as large as the global average in recent decades, known as Arctic Amplification (AA). At the same time, cold, snowy winters have been found over mid-latitude land areas, known as 'warm Arctic - cold continents' pattern. This pattern has had severe socio-economic impacts across the Northern Hemisphere. What happens in the Arctic does not stay in the Arctic. Several studies suggested a possible linkage between the AA and the change of weather pattern in the mid-latitude: 1) AA weakens the poleward temperature gradient and upper-level westerly winds; 2) wavier polar jet stream makes weather patterns move eastward more slowly; 3) extreme weather more likely. However, the physical mechanism of this linkage is still under debate. The goal of EuropeWeather is to create new knowledge of cold winter extremes in Europe in response to the AA. The project consists of the following activities: (1) analysis of the temporal and spatial changes of winter surface air temperature in Europe, with a focus on the extremely cold winters; (2) investigation of the changes in polar jet stream in response to the proceeding summer sea ice minima; (3) studies of the cold winter weather patterns in Europe and Atlantic sector according to the changes of the polar jet stream; and (4) synthesis and dissemination of results by publishing papers in high impact journals and dissemination of results from to a broader user community. The media, project webpage, Facebook etc. will also be efficiently used to communicate with the general public. In general, this project is progressing well according to our plan: 1) AA and 'warm Arctic - cold continents' pattern can be found both in the early 20th century warming period (1920s-1940s) and the current warming period (1990s - now). So far, we've analyzed the dynamical features of those severe winters during both warming periods based on the ECMWF ERA 20th Century Reanalysis data. The purpose is to provide better understanding and long-term perspective of the drivers of temperature variability in the mid-latitude. These results have been presented at seven workshops/conferences, which were specifically dealing with the 'linkage' issue. This is such a hot topic now, and we managed to get good scientific results, and valuable feedback from other scientists. A report from one of the workshops is published in Bulletin of the American Meteorological Society. Two peer-review papers are to be submitted to the International Journal of Climatology and the Environmental Research Letters. 2) International cooperation has taken place with our US partner. Prof. Jennifer Francis visited Nansen Center in January 2015 and October 2016. She made three guest lectures, which highlighted the research progress and chanllenges in this field, and particularly pointed out the difficulties of quantifying the impact of AA and associated sea ice and/or snow cover change on the mid-latitude weather, and the importance of compounding effect of sea surface temperature and sea ice on the extreme weather. One internal workshop with scientists/students who are working on 'linkage between Arctic climate change and mid-latitude weather' has also taken place in NERSC. 3) Project related work has been presented on Bjerknessenterets klimaforskningsdag in 2015 as a popular science presentation, which was given after the show of a documentary movie called ?Ice & Sky? by Luc Jacquet. The presentation was a good example of why the changes in ice matters, and was a successful cooperation with local community at Bergen International Film Festival.

Arctic region has been warming strongly in recent decades with a dramatic decrease of sea ice extent, but the recent few winters appeared to be extremely cold both in North America and Europe. This has brought enough surprises to the society with issues r elated to safety, energy and resource supply, public transport, etc. Both observational and modelling work suggested that the Arctic sea ice loss might have played an important role on the winter weather pattern. However, the robust dynamical link between proceeding summer sea-ice loss and winter weather in Europe still remains an open question. Francis and Vavrus (2012) hypothesized that the recent decline in Arctic summer sea ice extent has led to increased meandering in polar jet stream in the troposph ere. The increased meandering of the polar jet stream would cause the weather patterns in mid-latitudes to be more persistent, leading to an increased probability of extreme cold weather, following the record low sea ice minima. The EuropeWeather pr oject proposed here will carry out an innovative and fundamental research on investigating the impact of the summer Arctic sea ice loss on winter extreme weather pattern in European and Atlantic sector. The overall goal of EuropeWeather is to create new k nowledge of cold winter extreme weather patterns in Europe in response to the increased meandering of the polar jet stream caused by record low summer Arctic sea ice minima. The expected results of my research will be used to improve the understanding of this linkage and the winter extreme weather in Europe.