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Azores cyclone for years in hiding, probably never to return. What climate? »ILMETEO.it

Weather: Azores cyclone for years in hiding, probably never to return. What climate?

Why so runaway in the last summer periods? Let’s try to understand something…

Location and average impact of high pressure in the AzoresThe famous Azores cyclone, responsible for the pleasant Mediterranean summer, has been in hiding for many years. He seems to have disappeared, and is in fact a fugitive, who knows if he will come back again, let’s see what prospects there are.

HOW ANTICYCLONE WORKS Let’s remember some of its features. It is an anti-edematous character derived from the circulatory system that characterizes the famous Hadley Cell.
The Hadley hive is nothing more than a typical circulation of the tropics. In this part of the planet, the sun beats more strongly than in any other part of the globe. Thus, it is a highly heated region where the lighter warm air from the ground rises to the top according to the convention.
The rising air causes a depression over the land itself with extreme instability and the consequent torrential rains characteristic of the tropics. The air that has gone up, after it has cooled, ends up being heavier, accelerating down, more perpendicular to the north, in the hemisphere, in the subtropics.
Going down involves heating the air itself by pressure, and increasing pressure on the ground, resulting in semi-permanent anticyclones appearing in these subtropics. The Azores high pressure is one such area and occupies the Atlantic subtropics, with peaks often in correspondence with the Azores, west of Portugal, from which the name derives.

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Anti-African Cycles – Another Italian anticyclone, that is, those that directly interest us, cousin of the Azores, isNorth African subtropical cyclone We have gone through a number of fiery seasons in recent years.

Why did the Azoreans go? – But why wasn’t the summit of the Azores, the one that brought a mild and pleasant summer in the 1960s/80s, more pronounced? In our opinion there is an underlying reason. The high pressure effect of the Azores is closely related to the trend of Atlantic surface temperatures.

index love – There is an indicator, in particular, that determines its direction and is called the AMO indicator which stands for Atlanti Multidecadal Oscillation. The ocean surface temperatures vary, and according to this indicator, a more significant variation from positive to negative occurs in the 20/40 year phases, which is an average phase calculated with the latest systems, over 30 years or a little more.
In phases with positive average temperatures, the high pressure of the Azores finds it more difficult to survive with good continuity, since the atmospheric circulation, also resulting from the surface thermal state of the ocean, is more dynamic.
Moreover, there are greater fluctuations in the subpolar jet stream in the ocean strip, often near Portugal and the eastern Atlantic, precisely where the Azores should have maximum high pressure.

Positive love indicator – From 1995 The AMO index is in a positive phase, discouraging the state of good shape in the upper Azores. Average Summer Circulation Derived from Positive AMOAverage Summer Circulation Derived from Positive AMO
On the contrary, the more frequent eruptions of the subarctic jet west of Portugal are the cause, instead, of the altitude, the most numerous, in recent years, of high pressure in North Africa, with burning mostly in the central Mediterranean and in Italy (some of the fiercest past centuries) that occurred, especially in the last fifteen years (second picture ). Average Summer Cycle Passive DeadAverage Summer Cycle Passive Dead

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during periods I like the negativesa greater level of pressure is found in the Atlantic, especially in the summer months, with the Azores pressure rising further up to the northern mid-ocean latitudes and an unstable flow to the north, without many basins towards the mid-Atlantic latitudes especially in the east.

Conclusions and Reflections By doing a little math, compared to the above data, we realize that a positive AMO phase can turn into a conclusion, about 25 years after its fairly documented inception. Considering also that a sign change estimated at about 30 years is quite an indicator and volatile, the AMO+ phase could, within a few years, end with a gradual change of sign. It is reasonable to expect, therefore, that Possible return of high pressure to the Azores more frequently in the next five years, With a pleasant and warm summer, but without excesses. At the same time, there is less presence of high pressure in North Africa and associated flames.