Solar cycles & the weather
‘The sun’s activity waxes and wanes on an 11-year cycle, and over this cycle the amount of ultraviolet (UV) light the sun emits changes a lot more than does the total amount of energy. A study (published in Nature Geoscience in 2011) by Sarah Ineson of Britain’s Meteorological Office shows hows the severity of winters in Europe, and warming in the Artic, might be linked to changes in solar acitivity. The stratosphere is the part of the earth’s atmosphere which does most to absorb UV, and is thought to be most affected by the sun’s UV cycle. Dr Ineson found that at low UV levels the stratosphere in the tropics was cooler because there was less UV for it to absorb. This meant that the difference in temperature between the tropical statosphere and the polar stratosphere shrank. That changed the way the atmosphere circulated, and as those changes spread down into the lower atmosphere they made it easier for cold surface air from the Arctic to come south in winter. The Arctic was warmer than usual but northern Europe was colder,’ (abridged from ‘Climate and the solar cycle, Chilling out in the winter sun,’ The Economist October 15th 2011, p77).