Study prompts rethink of atmospheric circulation models
New research suggests that scientists may have to radically rethink their understanding of how air circulates in the atmosphere. The study, published in the journal Science, reveals that warm, moist air rising in the mid latitudes plays an important role in the circulation of air around the globe. The findings will help us to refine climate models and also boost our understanding of weather patterns in the mid-latitudes, which lie between 30 and 60 degrees north and south of the equator and take in much of Europe. 'With more attention than ever before being focused on understanding our planet's climate, weather systems and atmosphere, it's important that scientists challenge their own assumptions and current theories of how these complex processes work,' commented Dr Arnaud Czaja of Imperial College London in the UK, one of the authors of the paper. 'I think our study sheds new light on the driving forces behind the weather in the mid latitudes.' Previously, scientists thought there were two major air circulation 'cells' in the atmosphere: one in the northern hemisphere, the other in the southern hemisphere. According to this theory, warm air rises in the tropics and flows northwards before sinking back down to Earth at the poles. Together with colleagues in the US, Dr Czaja carried out a detailed analysis of meteorological data. Their results suggest that there are in fact two circulation cells in each hemisphere. In the first cell, air rises at the equator and falls at the subtropics. In the second cell, air rises in the mid latitudes and falls in the polar regions. According to Dr Czaja, previous theories failed to take into account the important role water vapour plays in mid-latitude weather systems. By allowing for this factor, the scientists found that much more air rises in the mid-latitudes than was previously thought, and as much as half of the air rising into the upper reaches of the atmosphere comes from the mid-latitudes. 'Our model suggests that there is a second cell of air in each hemisphere which is characterised by air rising, clouds forming, storms developing and other processes associated with moisture in the air occurring in the mid-latitudes,' said Dr Czaja. The findings have important implications for our understanding of climate change. 'As Earth's temperature rises, the amount of water vapour present in the atmosphere is extremely likely to increase as well,' the article concludes. 'Understanding how changes in temperature and humidity affect the dynamics of [...] circulation is a critical issue for better predicting mid-latitude climate in a warmer world.'
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