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EXCEPTIONAL HEAT WAVE, NEITHER NORMAL NOR CLASSIC, FOR THIS – The heat wave that affected a large part of Italy yesterday can be defined as anything but normal or even worse ‘summer classic’, as we have had the opportunity to read or hear on several occasions. Without the data that speaks for itself, with peaks of 46-47°C in Sicily, 45°C in Sardinia, and 41-42°C not only in the South but also in the Center (including Rome which in some districts broke its July record), let’s examine this heat wave in its characteristics to understand how anomalous it is.
First point: the intensity of the hot advection. The air mass we are interested in is directly extracted from the Sahara, therefore already very hot at this time of year and in a context of constant global warming, but accentuated in the central-western Mediterranean due to what is defined as anticyclonic subsidence. Specifically, the African high pressure, in this case characterized by particularly high geopotential values at an altitude of 5500 m, compressed the air mass downwards which became superheated and dried even more (due to the physical laws of gases). HEIn a free environment we find ourselves thus above the head, at about 1500-1600m of altitude, temperatures of 24-26°C and up to 28°C over Sicily and Sardinia. These are temperatures above average, even by 10-12°C, taking into account that at that altitude, always in a free environment, we should generally find temperatures between 14 and 18°C maximum. Let’s make one point clear right away: we are talking about air that is warmer and drier due to the effect of high pressure, but this is especially at high altitudes. On land, however, the warm advection ‘picked up’ moisture from the Mediterranean Sea, resulting in markedly muggy conditions, especially along the Tyrrhenian coasts and in northern Italy in general.
Second point: extension. The intense core of the heat wave icovers almost the entire western Mediterranean and south-central Italy, while the North stayed further out even though temperatures were still above average and the heat was skyrocketing. So we are not talking about temperatures above average 10-12°C in restricted areas of the Peninsula, but essentially over a large part of south-central Italywhile in the North the anomalies were less marked (in fact, only in this macro area was the heat not exceptional, no matter how intense it was)
Third point: duration. That’s not all: this heat wave will continue with intensity for the next few days, although it will subside in the Center-South over the weekend (even earlier in the North), but it will probably regain strength next week, especially in the South, so we are not talking about an exceptional heat hit and run, but a phase that could last another 8-9 days, although with some physiological modulations.
THE COMPARISON WITH THE TEMPERATURES OF NORTH AFRICA AND SAUDI ARABIA – To minimize this heat wave, comparisons were also made with temperatures in North Africa and Saudi Arabia, where the peaks were higher than those in south-central Italy, in some cases not even as high, labeling those peaks as true extreme heat. However it does not make sense to compare the Italian thermal peaks with those of the United Arab Emirates or North Africa, characterized by a context and climatic averages decidedly different from ours: in simple terms, it is wrong to think that if in Italy it is not 45-50°C as in Saudi Arabia, then the heat is not abnormal; for Italy it is already from the moment that 38-40°C is reached.
AFRICAN ANTICYCLONE, LET’S CLEAR – If it is true that the atmospheric pressure can be modest on land, since hot air weighs less, it does not mean that we are not facing an anticyclone, even if it is of exceptional power. This is what we are witnessing these days and its strength is measured by the so-called height geopotentials, which in this phase are particularly high between the coasts of North Africa, the western Mediterranean and central-southern Italy (it is the so-called dynamic anticyclone, which differs from the thermal one fed by heavy cold air on the ground during the winter season). Technically we are dealing with a subtropical anticyclonic promontory, whose roots are not oceanic (as in the case of the Azores anticyclone), but North African, and that is why it is called the African anticyclone, although its center of gravity may temporarily unbalance beyond North Africa towards Europe or Italy as in this case. It is always the protagonist of the fiercest heat waves over Italy, regardless of the imaginative names attached to it. The high pressure of the Azores is always part of the same family of subtropical anticyclones, it is a cousin of the African one, but with the difference that it is fed by oceanic air, still warm, but not as warm as that of the Sahara. For this reason, when we are facing the Azores anticyclone, the heat is generally less intense and more bearable. However, it must also be said that in an era of constant global warming, the air masses that feed the anticyclones, be they oceanic or Saharan, are already on average warmer than in the past.
HEAT WAVES HAVE ALWAYS BEEN THERE; TRUE BUT… – Yes, there have always been heat waves, even very intense ones: let’s remember the one in the summer of 1983 when Rome reached 40°C in July. The point is that events were once decidedly less frequent and long lasting than they are today. Particularly hot summers were also that of 1987, then that of 1994, but 1998 raised the bar: from that year to today, heat waves have experienced an increase in frequency. Let’s think back to a new bar in 2003 to the last decade that saw hotter and hotter summers with record after record gradually getting closer over the years. This is not to say that there aren’t cooler, more unstable phases or summers just above average or in the average, like 2002 and 2014, but it does mean that there are increasingly sporadic cases, exactly the opposite of what happened before the late 90s. You want to think in metaphors: before, everyone used to get sick from time to time, but if in recent years we’ve gotten sick much more frequently, it means something is wrong (even though sometimes we’re still fine). ). More details in this article.
THE CLIMATE HAS ALWAYS CHANGED; TRUE BUT… – The climate on earth has always changed reflecting precise natural cycles; certainly in the past there have been climatically warmer periods than at present. The crucial point, however, is the time scales: natural climate cycles occur over millennia.which also allows an adequate readjustment of the ecosystems. The climate change we are witnessing today is, in contrast, extremely rapid and acts on time scales on the order of decades, not millennia: we are all realizing it. And it is at this speed that anthropic forcing takes over, which is therefore added to the natural one, since this acceleration of climate change has been occurring since the industrial era. Going back to thinking in metaphors: it is natural that we age, but if we suddenly find ourselves at 40 with the equivalent of 80 years of age, something is wrong.
THE SIDE OF THE HEAT MEDAL, VIOLENT THUNDERSTORMS – Warm, moist air is the primary fuel for thunderstorms. Clearly in such an intense heat situation, the phenomena Once developed, storms can manifest themselves with particular violence, having much more energy available, yet being dangerous.. This has already happened in the Alps, but generally the north in the coming days will be at risk of very intense storms associated with large hail and sudden violent gusts of wind with potential damage. The price to pay for a partial upgrade.
Check the situation live also through the eye of geostationary satellites reworked by our team. Here the section >> Satellites.
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