The person responsible for the absence of winter in most of Europe, including Italy, where temperatures will be recorded from the end of April over the weekend, is a polar vortex that has reached record values. It is, as explained by the expert Meteorologist Rino Cutuli on IconClima, "of a large circulation of low pressure at high altitude, a real top with circular motion counterclockwise, full of very cold air inside, which is stationed in semi-permanent way above the vertical of the North Pole, at an average altitude between 10 and 30 Km approximately ". A measure of the intensity of the polar vortex is given by the Arctic Oscillation (Ao), an index calculated on the basis of the pressure difference detected between the Arctic and the medium-low latitudes. This index can go through two phases: a positive and a negative one.
When it is positive, the polar vortex is particularly deep and active, the cold air remains harnessed inside it without having the possibility of escaping from its natural location, generating a flow of temperate, slightly wavy western currents (from west to east), which they flow intensely from west to east and consequently limit heat exchanges between high and low latitudes. The result is a predominantly stable and milder than normal time on North America, Central and Southern Europe and much of Asia.
On the contrary, when the Ao is negative, the shreds of the polar vortex have the opportunity to migrate south, causing more or less intense irruptions of very cold air towards the medium-low latitudes. "Last February 10 - continues the meteorologist of Meteo Expert - the record value of + 6.34 of the AO index was reached, comparable to that measured in the winter of 1975-76, confirming a very strong polar vortex, from record, and a practically non-existent winter in over three quarters of Europe, with exceptionally mild temperatures and far beyond the norm. And it did not end there, because at the end of the month a new record peak is expected, higher than the latter just reached ".