Less Summer Arctic Sea Ice Cover Means Colder, Snowier Winters in Central Europe

[jpak]

http://www.sciencedaily.com/releases/2012/02/120201105126.htm

Even if the current weather situation may seem to speak against it, the probability of cold winters with much snow in Central Europe rises when the Arctic is covered by less sea ice in summer. Scientists of the Research Unit Potsdam of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association have decrypted a mechanism in which a shrinking summertime sea ice cover changes the air pressure zones in the Arctic atmosphere and impacts our European winter weather.

These results of a global climate analysis were recently published in a study in the scientific journal Tellus A.

If there is a particularly large-scale melt of Arctic sea ice in summer, as observed in recent years, two important effects are intensified. Firstly, the retreat of the light ice surface reveals the darker ocean, causing it to warm up more in summer from the solar radiation (ice-albedo feedback mechanism). Secondly, the diminished ice cover can no longer prevent the heat stored in the ocean being released into the atmosphere (lid effect). As a result of the decreased sea ice cover the air is warmed more greatly than it used to be particularly in autumn and winter because during this period the ocean is warmer than the atmosphere. "These higher temperatures can be proven by current measurements from the Arctic regions," reports Ralf Jaiser, lead author of the publication from the Research Unit Potsdam of the Alfred Wegener Institute.

The warming of the air near to the ground leads to rising movements and the atmosphere becomes less stable. "We have analysed the complex non-linear processes behind this destabilisation and have shown how these altered conditions in the Arctic influence the typical circulation and air pressure patterns," explains Jaiser. One of these patterns is the air pressure difference between the Arctic and mid-latitudes: the so-called Arctic oscillation with the Azores highs and Iceland lows known from the weather reports. If this difference is high, a strong westerly wind will result which in winter carries warm and humid Atlantic air masses right down to Europe. If the wind does not come, cold Arctic air can penetrate down through to Europe, as was the case in the last two winters. Model calculations show that the air pressure difference with decreased sea ice cover in the Arctic summer is weakened in the following winter, enabling Arctic cold to push down to mid-latitudes.

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