The Changing Arctic Cryosphere: Snow And Sea Ice Impact On Prediction And Climate Over Europe And Asia

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2015

End date

12/31/2019

Budget

597,903 EUR

Fundings

Abstract

Climate change is occurring rapidly in the Arctic, and climate models project further extensive changes later in this century. Global warming is enhanced at high northern latitudes where the Arctic surface air temperature has warmed at twice the rate of the global average in recent decades - a feature called Arctic amplification. The rapidly shrinking Arctic cryosphere has become the most visible aspect of climate change. On the other hand, North America, Europe, and East Asia have experienced anomalously cold winters with record high snowfalls during recent winters, associated with a negative phase of the North Atlantic Oscillation. These cold winters had increased occurrences of cold air outbreaks from high latitudes. These rapid changes in both the snow and sea ice extent observed in the northern regions may affect the atmospheric circulation and extreme weather events down to middle latitudes. There a need to better understand the connections between the decline in summer Arctic sea ice and the build-up of the Eurasian snowpack in the following autumn, and their impacts on the winter circulation. The overall goal of the SNOWGLACE project is to improve our understanding of the complex interconnections and feedbacks in the Arctic region, their role in the rapid and unprecedented climate changes in the north, their impacts on extreme weather events in mid- to high-latitudes. It also aims to assess the impact of changing sea ice and snow cover on the predictability of extreme weather events on the seasonal time scale. New results from the project are that climate re-analyses over both the recent Arctic warming and the early 20th century Arctic warming show similar linkages between sea ice reduction over the Barents Sea and build-up of snow over parts of Siberia. The Barents Sea has also been identified as a key region where the June sea-ice variability exerts the most significant impacts on the East Asian summer rainfall. A reduction in June sea ice excites persistent anomalous upward air motion due to strong near-surface thermal forcing, which further triggers an east-west Rossby wave train known as the Silk Road pattern, extending to East Asia. To demonstrate that snow initialisation influences surface temperature over Eurasia and can improve model prediction skill, we carried out a large ensemble seasonal simulations with the Norwegian Climate Prediction Model. NorCPM consists of the Norwegian Earth System Model (NorESM) and advanced initialisation and assimilation techniques to make initialised predictions. The results reveal that snow initialisation improved the prediction skill for wintertime surface temperature over Eurasia, up to 2 months in advance. The benefits and key practical implementations for the assimilation of sea ice concentration in the NorCPM have been investigated in a perfect model framework. First, it is found that a flow-dependent, strongly coupled ocean?sea ice assimilation method outperforms weakly coupled (sea ice only) assimilation. Extending the ocean updates below the mixed layer is slightly beneficial for the Arctic hydrography. Second, using a multicategory of sea ice greatly reduces the errors in the ice state. The role of snow depth as a predictor of temperature one month ahead in the Northern Hemisphere has been elucidated for different seasons, in comparison to other predictors like soil temperature or soil moisture. Snow depth is an important mediator when, and where, its interannual variability is large: in winter at midlatitudes and in spring and autumn at high latitudes. We found an important role of the Atlantic Multidecadal Oscillation (AMO) in modulating the atmospheric response to the declining Arctic sea ice, with Eurasian snow cover and the stratosphere playing a role in the linkages. We discovered that sea surface temperatures over the Atlantic modulate the atmospheric response to the sea ice decline. During a cold AMO phase, increased Ural blocking activity and associated northerly cold air advection and moisture transport from the Arctic leads to an extended snowpack and a cold continent anomaly over Eurasia in December. The enhanced upward propagation of planetary waves into the stratosphere over the Siberian?Pacific sector leads to a weakened stratospheric polar vortex and a negative Arctic Oscillation (AO) phase at the surface in February. We also found that the North American snow cover influences the Eurasian surface temperature downstream with a 1-month lag, through a mechanism involving sea surface temperatures and synoptic weather systems over the North Atlantic. Another result is that the stratospheric sudden warming of February 2018, linked to cold air outbreaks over Europe, Asia and North America was associated with a precursory ridge over the Urals and high snow cover over Eastern Eurasia, the latter contributing to intensifying upward planetary wave propagation.?