By Elisabeth Halvorsen, UiT/The Nansen Legacy
Arctic sea ice and the weather in northern Europe
In atmospheric science, teleconnections are linked, climate anomalies that occur in widely separated regions on the globe. One well-known example is the North Atlantic Oscillation (NAO), a fluctuating weather phenomenon controlling the strength and direction of westerly winds across the North Atlantic. It has been postulated that reduced sea ice concentrations in the Barents- and Kara Sea in autumn may trigger changes in the stratosphere that force the NAO into a negative phase. Camille Li (UiB) and colleagues were able to find evidence for this proposed causal linkage, meaning that reduced Barents-Kara sea ice in autumn can lead to decreased storminess, below-average precipitation, and lower-than-average temperatures in northern Europe – all weather phenomena of a negative NAO. However, the linkage is highly intermittent: it has been particularly apparent in recent decades, but may not be a systematic feature of the climate system.
Spring Siberian snow and the Atlantic jet stream
Another teleconnection, described in a publication by Nansen Legacy researcher Fei Li (UiB) and co-authors, is the mechanism by which anomalously little snow in Siberia in spring result in significant tropospheric warming that ultimately leads to a weakening of the Atlantic jet stream – a fast flowing meandering air current over the northern hemisphere – and influence sea surface temperatures over the North Atlantic.
Photo: Christian Morel/ christianmorel.net
Hot cyclones traveling in from the south
The Atlantic jet stream also has an impact on how many cyclones reaches the Barents Sea from the North Atlantic. In a recent study, Erica Madonna (UiB) and Camille Li (UiB), with others, were able to show that more cyclones reach the Barents Sea when the jet stream is angled towards the Barents Sea. On the other hand, there are fewer cyclones entering when a quasi-stationary high-pressure system over the Barents Sea blocks the cyclones. Cyclones transport warm and moist air from the mid-latitudes. Consequently, they can have a strong impact on the Arctic sea ice through warming and ice melt, sea ice drift and break-up. Both the birthplace and the path cyclones take to reach the Barents Sea have a say in their impact. The study shows that winter cyclones originating in the North Atlantic south of 60°N produce the strongest warming in the Arctic. The location of the sea ice edge has also been proposed by previous studies to affect the path of cyclones, because it creates a strong surface temperature gradient that the cyclones may use as fuel to grow. The recent retreat of sea ice in the Barents Sea could thus be steering the cyclones further north and not east into the Barents Sea, resulting in a poleward shift of the storm tracks. However, the study could not find evidence to support this effect of the sea ice on cyclone paths.
“Thus, we conclude that the atmospheric circulation rather than the sea ice location controls the path of cyclones at high latitudes.”
Erica Madonna, UiB
References:
Madonna E, Hes G, Li C, Michel C, Siew PYF (2020) Control of Barents Sea wintertime cyclone variability by large-scale atmospheric flow. Geophysical Research Letters 47: e2020GL090322. doi.org/10.1029/2020GL090322
Shen H, Li F, He S, Orsolini YJ, Li J (2020) Impact of late spring Siberian snow on summer rainfall in South-Central China. Climate Dynamics 54: 3803-3818. doi.org/10.1007/s00382-020-05206-5
Siew PYF, Li C, Sobolowski SP, King MP (2020) Intermittency of Arctic–mid-latitude teleconnections: stratospheric pathway between autumn sea ice and the winter North Atlantic Oscillation. Weather Climate Dynamics 1: 261-275. doi.org/10.5194/wcd-1-261-2020