Azores high
The Azores high is a high pressure area that is effective as a center of action , which develops in the area of the Azores in the North Atlantic and plays a decisive role for the weather in Central Europe .
Emergence
The Azores high belongs to the subtropical high pressure belt of the North Atlantic and arises on the edge of a vortex of the polar front jet stream . In general, the Azores high and Iceland low play the decisive role for the large-scale weather conditions in Europe : Mostly the low pressure systems (cyclones) driven by the general west drift in the northern hemisphere come from the North American coast across the Atlantic ( Atlantic west weather). Depending on the characteristics of the two systems (expansion and pressure difference), the low pressure eddies ( North Atlantic lows) are shifted to the south or north, so that the individual areas of Europe are hit by the center, by the warm front or the cold front .
The Azores high moves in a seasonal rhythm. In the long-term mean (1881–1995) the Azores high center is 33 ° N in winter and 34.5 ° N in summer, the mean location varies from the Azores 1400 nautical miles to the northeast and about 1500 nautical miles to the southwest, with extreme locations being present Ireland , Newfoundland and the Canary Islands as far as the West African coast were measured, both in summer and winter. The mean air pressure is 1025 hPa , with monthly mean fluctuations between 1034 and 1016 hPa.
At some times the Azores high extends in the form of a wedge, mostly over the Biscaya to Central Europe ( Western Europe high ); if a high-pressure cell becomes detached, it can move as far as Scandinavia . If the wedge connects to a continental high ( e.g. over Russia) , it is also known as an omega high (after the Ω- shaped, far northward expansion between two centers) - such a highly stable situation led to the 2003 heat wave , which lasted two weeks in August led to temperatures of around 40 ° C in Central Europe.
In addition, the Azores high also affects the formation and trajectory of the hurricanes : On the one hand, the southern extension of the Azores high influences the formation of the Atlantic tropical cyclones, on the other hand, the western extension steers the more mature cores either towards the Caribbean or they circle the Azores high off the American east coast, and then sometimes transform into normal Atlantic lows that can also reach Europe.
Effects over the course of the year
If the Icelandic low and the Azores high are pronounced in the winter and there is therefore a large difference in air pressure , a mild westerly wind occurs, the winter is rather humid. With a low pressure difference, on the other hand, the cold, dry air over Eastern Europe (Russia high) determines the winter weather in Central Europe.
In spring, when the sun rises at its zenith and the Azores high migrates north, more air that has warmed up over the Gulf Stream is transported to Europe. At this time, the weather is typically unstable (late winter, often heavy fresh snow events, late winter storms and winter thunderstorms up to April weather , with rapid build-up of the Azores high also premature heat waves)
Even in summer, the Icelandic low and the Azores high determine whether the summer is rainy, changeable or stable. According to current interpretation, the “dormouse rule” (the weather on / around the dormouse day lasts 40 days) corresponds to the meteorological question of where and how powerfully the Azores high built up after the summer solstice .
At the beginning of autumn there are often only slight differences in air pressure when the temperatures of the sea and land masses are equal: The weather is calm ( Indian summer ) , when it cools down, the westerly weather arrives unhindered (autumn orca) until the wintry Azores high has stabilized again .
- Examples of the effects of the Azores high
Atmospheric waves in the tropics ...
... and the location of the Azores / Bermuda highs control the formation and migration routes of the hurricanes
An Azores high (Biskayalage) and a North Sea low lead to an ingress of polar cold air into the Mediterranean area: Mistral
Long-range effects: The North Atlantic and Arctic Oscillation
In multi-year cycles (around every 7 years), winter weather conditions with large pressure differences between the Azores high and Iceland low are replaced by winters with minor differences. This phenomenon is called the North Atlantic Oscillation (NAO). Your index describes the relationship between the position and extent of the Azores high and the jet stream . The effect of the polar vortex on the location and intensity of the Icelandic lows is represented by the Arctic Oscillation (AO). This index represents a relationship up to the Pacific area ( teleconnection ).
media
- Azores high & Iceland low . Series universe . Kurt Mayer (book), Dieter Pochlatko (producer), Andreas Jäger (moderation), Kurt Adametz (music); ORF , undated ( shop.orf.at )
Web links
- Azores. Weather kitchen of Europe . The main topic of the week, scinexx (May 2, 2003)
Individual evidence
- ↑ meteorologically speaking, according to the direction from which the wind is coming
- ↑ a b c Azorenhoch ( Memento from November 1, 2013 in the Internet Archive ) , DWD (pdf; 163 kB)
- ↑ see graphic in Azorenhoch , DWD
- ↑ a b Weather rule cases / singularities: dormouse , severe weather center
Coordinates: 34 ° N , 30 ° W