What does a positive AO mean?
What does a positive AO mean?
Highlights. The Arctic Oscillation (AO) is a back-and-forth shifting of atmospheric pressure between the Arctic and the mid-latitudes of the North Pacific and North Atlantic. When the AO is strongly positive, a strong mid-latitude jet stream steers storms northward, reducing cold air outbreaks in the mid-latitudes.
What is AO mode?
The Arctic oscillation (AO) or Northern Annular Mode/Northern Hemisphere Annular Mode (NAM) is a weather phenomenon at the Arctic pole north of 20 degrees latitude. It is an important mode of climate variability for the Northern Hemisphere.
What is AO index?
The AO Index (Arctic Oscillation Index) describes the difference of the air pressure between the Arctic and mid-latitudes. The stronger this difference, the stronger the West Wind Drift blows air masses from the North Atlantic to northern Europe and Siberia.
How is AO index calculated?
The AO index is calculated by projecting 1000 hPa geopo- tential height anomalies onto the loading pattern of the AO. This loading pattern is de- fined as the leading empirical orthogonal function (EOF1) of monthly mean 1000hPa geopotential height anomalies poleward of 20◦N during 1979–2000.
What is a negative AO?
When the AO is in the negative phase there is higher-than-normal pressure over the polar region and lower-than-normal pressure at about 45 degrees north latitude. The negative phase allows cold air to plunge into the Midwestern/Eastern United States and Western Europe, and storms bring rain to the Mediterranean.
How does Arctic Oscillation influence local weather?
Pressure differences manifested in the AO affect Earth’s atmosphere and people’s lives, particularly in winter. “When the Arctic Oscillation is in its positive phase, the jet stream, which brings us much of our weather in middle latitudes, tends to shift to the north,” Serreze said.
What is the Northern Annular Mode?
Northern Annular Mode (NAM) also known as Arctic Oscillation (AO) or Northern Hemisphere Annular Mode, is a natural form of climate variability, being closely associated with the North Atlantic Oscillation (NAO), which has similar structure over the Atlantic but when looked at from above, the shape is more annular.
What is Northern Annular Mode?
Why is Nao important?
Especially during the months of November to April, the NAO is responsible for much of the variability of weather in the North Atlantic region, affecting wind speed and wind direction changes, changes in temperature and moisture distribution and the intensity, number and track of storms.
Why is NAO important?
Will there be a polar vortex in 2021?
The Polar Vortex has just returned for the cold season 2021/2022, yet it is already facing its first stratospheric warming event. An unusually early warming event is starting over the Polar regions, with more warming forecast to follow into the late month.
What causes the Arctic Oscillation?
The polar vortex does not come and go; it is a permanent feature of the Earth system. Still, the vortex’s shape changes over time, affected by shifts in atmospheric pressure and temperature. Scientists describe these pressure and temperature shifts as changes in the AO.