Weatherwatch: what is the North Atlantic Oscillation?

There is uncertainty over the future behaviour of this important weather phenomenon in a warming climateThe North Atlantic Oscillation is a numerical index and a large-scale expression of westerly wind strength over the North Atlantic, often associated with the strength of low pressure over Iceland. Positive values are usually defined by a deep area of low pressure here, while negative values often coincide with a nearby area of high pressure.In north-west Europe, a positive winter North Atlantic Oscillation (NAO) generally coincides with above-average temperatures, storminess and precipitation due to increased westerly wind strength. A negative winter NAO is often associated with drier and colder conditions owing to more frequent easterlies and northerlies. The summer NAO is less influential as relationships between weather and atmospheric circulation are more localised. Continue reading...