EGU2020-19188
https://doi.org/10.5194/egusphere-egu2020-19188
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Occurrence and mechanisms of extreme winter air temperatures in the Arctic and surrounding continents

Timo Vihma1, Petteri Uotila2, Tuomas Naakka1, and Tiina Nygård1
Timo Vihma et al.
  • 1Finnish Meteorological Institute, Meteorological Research, Helsinki, Finland (timo.vihma@fmi.fi)
  • 2Atmospheric and Earth System Research (INAR)/ Physics, University of Helsinki, Helsinki, Finland

The recent rapid warming of the Arctic atmosphere and ocean and related sea ice decline have been associated with increasing occurrence of extreme weather events in the Arctic. Applying ERA-Interim reanalysis, we identify 100 days with largest positive and negative anomalies (compared to local climatology) in 2-m air temperature (T2m) in the Northern Hemisphere in winter during 2005-2019, and address various physical mechanisms contributing to these events. The mechanisms responsible for warm extremes in the Arctic are often associated with a meandering Polar front jet stream, favouring cases of large transports of heat and moisture from mid-latitudes to the Arctic. In addition, subsidence heating often contributes to warm extremes in the Arctic, allowing them to occur also under high-pressure conditions. The coldest T2m anomalies north of 30oN mostly occur in regions that are also climatologically cold, i.e., cannot be strongly affected by cold-air advection. This suggests a dominating role local surface energy budget and boundary-layer processes.

Extreme weather events often interact with anomalies in sea ice concentration. Cases of strong winds transporting warm, moist air masses to the Arctic provide both dynamic and thermodynamic forcing for large sea ice anomalies, and during winter the openings in sea ice field contribute to air temperature extremes via large heat fluxes from the ocean to atmosphere.

Coldest winter extremes in mid-latitudes are typically associated with meandering jet stream and high-pressure blockings, but show differences between Central Europe, North America and northern China. In Central Europe the coldest events are typically associated with cold-air advection from the East or Northeast, whereas during the coldest events in North American East Coast the cold air is transported from the North. In northern China, the coldest events often occur under high-pressure conditions with weak winds. Accordingly, the role of cold-air advection is much smaller than in the case of the coldest events in North America.

How to cite: Vihma, T., Uotila, P., Naakka, T., and Nygård, T.: Occurrence and mechanisms of extreme winter air temperatures in the Arctic and surrounding continents, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19188, https://doi.org/10.5194/egusphere-egu2020-19188, 2020

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Display material version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-19188, David Docquier, 05 May 2020

    Dear Timo,

    This is a very interesting study.

    Are you planning (or have you already done it) to apply this methodology to CMIP-type models to see whether they can represent these features?

    Thanks for your response.

    David