it was not predictable, the fault of the African anticyclone

it was not predictable, the fault of the African anticyclone
it was not predictable, the fault of the African anticyclone
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Marche on its knees, especially the areas of Senigallia and the Alto Pesarese, on the border with Umbria. It is the consequence of the violent storm that struck two days ago and which at the moment has caused 9 deaths, enormous damage to homes and structures and hundreds of displaced persons. It was essentially the strongest storm ever recorded in the Marche in the last ten years, given that, in some areas, 400 millimeters of water fell in a few hours: in a year it normally rains 1,200.

We are facing yet another proof of climate change, he explained to us in this interview Vincenzo Levizzani, research director of the Institute of Atmospheric and Climate Sciences of the Cnr of Bologna and professor of cloud physics at the University of Bologna: “The extremely high temperatures of the last few months, completely out of the norm compared to what we were used to, have caused a large mass of hot air, especially from the sea, which collided with cold air from the north”. And unfortunately, events like what happened in the Marche are not scientifically predictable.

The term “water bomb” is used a lot when events like this happen. Is it a scientific term? What actually happened?

Water Bomb is colloquial terminology, it says nothing. What we have witnessed is a phenomenon that can be classified from the point of view of science as an extremely intense storm. They are found at the top of the statistic as the precipitation intensity of a single thunderstorm event.

Is the self-regenerating temporal term scientifically appropriate?

It is still another matter. The thunderstorms themselves, that is, the individual storm cells, last half an hour, up to an hour. On the other hand, when we see these phenomena of longer duration and which drain a lot of water, it means that the storm has produced, in the jargon “has given birth”, secondary storms.

How does this phenomenon happen?

The storm is essentially formed by the collision between an ascending current, which is that of hot air that carries the water vapor upwards, causing the storm, and a current of cold air, which is discharged together with the precipitation, because the latent heat stored. This current of cold air reaches the ground and expands in all directions, because it finds the obstacle of the ground. It is as if it were a cold front that we are used to seeing in the weather maps in winter. This cold front wedges itself under the warm air and generates more thunderstorms, as happened two days ago.

Is the fact that temperatures in recent months and even these days have been higher than normal the cause of these storms? And can a self-healing storm happen in winter?

It is very difficult. It is happening now because we have seen the African anticyclone stand still on the European continent for months, bringing the temperature to levels beyond the norm, even to 40 degrees. Everything has warmed up, even the sea. These storms in the Marche were also fueled by the very hot and humid air coming from the sea.

So the reason lies in climate change?

Exactly. Years ago we used to have the Azores anticyclone stationed in the summer, a high pressure area with good weather and maximum summer temperatures of 35 degrees. We live in that part of the globe called temperate latitude. This anticyclone brought air to 4 kilometers of altitude quite cool coming from the ocean.

Instead the African anticyclone?

It has always existed too, but the novelty is that it has moved further north of the globe, bringing extremely hot air to a height of 2-3 kilometers. In both cases the air at a certain point heats up by one degree every ten kilometers as it descends. If the air is already very hot, as in this summer, such thunderstorms occur.

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Are they predictable?

These thunderstorms are hardly predictable.

How come?

They are due, as we said, to the pre-existing hot summer air that we still have because the temperatures are still high. With descents of cooler air from the north it creates an energy release in local thunderstorms. There are also several reasons why they are unleashed in certain areas: for example, it may depend on the presence or absence of mountains. However, predicting them is an extraordinary difficulty. Meteorological models are very difficult, non-hydrostatic models are needed, and there are some. The only thing that can be predicted is whether there is a lot of atmospheric instability in an area ready for an energy release, but to say that there will be a self-generating thunderstorm at that exact point is practically impossible.

It is said that there will be strong instability in the north in the coming days, is that right?

Strong winds and rains are expected that will pass from the North to the Center and then to the South, it seems that temperatures are decreasing, but we cannot say that extreme events such as that of the Marche are possible. We are heading towards autumn, so obviously there will be instability, but it will take a while, because these temperatures are really still very high. But this instability is expected to end soon, already on Saturday.

(Paolo Vites)

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The article is in Italian

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