快猫短视频

WHETHER it will be a harsh winter in London and New York at the end of this
year may depend on how much snow falls in Siberia. Researchers in Massachusetts
have found that high levels of Siberian snow cover in autumn lead to
particularly cold snaps in Western Europe and the Eastern US a few months
later.

鈥淭hink of Siberia as the refrigerator for much of the northern hemisphere,鈥�
says Judah Cohen, a climate dynamics researcher with Atmospheric and
Environmental Research, in Lexington, Massachusetts. Although the researchers
haven鈥檛 finished analysing their most recent data, early results suggest that
snow cover in Siberia was high last autumn, explaining the colder weather in the
eastern US this winter.

Cohen and his colleagues at the Massachusetts Institute of Technology in
Cambridge believe that Siberian snow directly affects a massive pressure system
known as the Siberian High, one of three dominant winter systems in the northern
hemisphere. Heavy snow reflects sunlight away from the Earth. This cools the
pressure system, making the air denser and heavier, so the Siberian High spreads
out more than usual.

Mountains prevent much of this air moving east and south. Instead, the
Siberian High sends colder air first west into Europe and then north over the
pole and down into the eastern US. Lower than average snowfall in Siberia has
the opposite effect, causing the High to shrink.

Cohen says the relationship, uncovered through analysis of data from 1972 to
1999, is strong enough to account for about one third of the variation in winter
temperatures in affected regions.

The Siberian High appears to dominate one of the other two main northern
hemisphere pressure systems. The second system sits mainly over the Pacific and
is relatively unaffected. But high pressures spreading over the Arctic help to
control the North Atlantic Oscillation, a complex flip-flopping of atmospheric
pressure over the Atlantic that plays a major role in determining the region鈥檚 weather
(快猫短视频, 13 January, p 18).

Martyn Clark, a climatologist at the University of Colorado in Boulder, says
one of the most important aspects of the work is that it moves beyond the focus
on sea surface temperature changes such as El Ni帽o and La Ni帽a in
predicting regional climate.

鈥淗e鈥檚 made some really important steps to uncover new relationships between
snow cover and climate,鈥� says Clark. However, Cohen and Clark agree that a
fuller understanding of these relationships will be needed before government
forecasters can begin using them to make long-term predictions.