Environmental Engineering Reference
In-Depth Information
The North Atlantic Oscillation (NAO):
This is the name given to year-to-year variations in the relative strengths and locations of the
Azores High and the Icelandic Low. A large difference in pressure between the two systems
(known as an index of NAO + ) leads to increased moist westerly winds, giving cool summers
and mild wet winters in Europe. Alternatively, when the pressure difference is low (NAO ),
the moist westerly winds weaken, resulting in cold winters in Europe. Cyclones then track
further south into the Mediterranean and over North Africa.
Under NAO + conditions, northern Canada and Greenland are colder and drier, but this
situation is reversed during a NAO phase. The NAO also exerts an influence on winter
weather over much of eastern North America. When the index is high (NAO + ), the Icelandic
Low reflects a strong south-westerly circulation of air over this region at the expense of Arc-
tic air moving south. Particularly during El Niño years, this results in warmer winters over
the north-eastern United States and south-eastern Canada. During NAO years, cold air is
able to penetrate further south and the eastern and south-eastern North American continent
experiences winter cold outbreaks as far south as Florida.
Search WWH ::




Custom Search