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6 minutes, 58 seconds heat dome, genesis of an exceptional heat wave
EXCEPTIONAL HEATWAVE, NOT NORMAL NOR CLASSIC, THIS IS WHY – 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. Net of the data that speak for themselves, 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 beat the its July record), let’s analyze this heat wave in its characteristics to understand how anomalous it is.
First point: the intensity of hot advection. The air mass we are interested in is of direct Saharan extraction, therefore in itself already very hot in this period of the year and in a context of constant global warming, but further exacerbated in the central-western Mediterranean by what is defined as anticyclonic subsidence. Specifically, the African high pressure, in this case also characterized by particularly high geopotential values at an altitude of 5500m, compressed the air mass downwards which was thus further overheated and dried (due to the physical laws of gases) . THEIn a free atmosphere we thus found ourselves on 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 the average, even by 10-12°C, considering that at that altitude, always in a free atmosphere, we should generally find temperatures between 14 and 18°C at the most. Let’s make one point clear right away: we talked about further overheated and dried air due to the effect of high pressure, but this above all at high altitudes. On the ground, however, the warm advection ‘collected’ the humidity of the Mediterranean Sea, which is why we instead suffered markedly sultry conditions, especially along the Tyrrhenian coasts and in Northern Italy in general.
Second point: extension. The intense core of the heat wave iencompasses almost all of the western Mediterranean and central-southern Italy, while the North remained more on the margins even though the temperatures were still above average and the heat was skyrocketing. We are therefore not talking about temperatures above the average of 10-12°C on restricted areas of the Peninsula, but essentially over a large part of central-southern Italywhile in the North the anomalies were less marked (in fact only in this macro area was the heat not exceptional, however intense)
Third point: duration. That’s not all: this heat wave will continue to continue with intensity over the next few days, even if it subsides in the Centre-South by the weekend (even earlier in the North), but will probably find new strength next week, especially in the South. We are therefore not talking of a hit and run from the exceptional heat, but of a phase that could last another 8-9 days, albeit with some physiological modulations.
THE COMPARISON WITH THE TEMPERATURES OF NORTH AFRICA AND SAUDI ARABIA – In order to minimize this heat wave, comparisons were also made with the temperatures of North Africa and Saudi Arabia, where the peaks were higher than those of Central-Southern Italy, in some cases not even that much, labeling those peaks as true extreme heat. However it makes no 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 it is not 45-50°C in Italy as in Saudi Arabia then the heat is not abnormal; for Italy it is already from the moment in which 38-40°C is reached.
Heat dome
AFRICAN ANTICYCLONE, LET’S GET CLEAR – If it is true that atmospheric pressure can be modest on the ground, as warm air weighs less, this does not mean that we are not dealing with an anticyclone, even of exceptional power. This is what we are witnessing these days and its strength is measured by the so-called geopotentials at altitude, which at this stage are particularly high between the coasts of North Africa, the western Mediterranean and central-southern Italy (we are talking about the so-called dynamic anticyclone, which differs from the thermal one fed by the cold heavy air on the ground during the winter season). Technically we are dealing with a subtropical anticyclonic promontory, whose roots however are not oceanic (as for the Azores anticyclone), but North African, and it is for this reason that it is called the African anticyclone, even if its center of gravity can temporarily lean beyond North Africa towards Europe or Italy as in this case. He is always the protagonist of the fiercest heat waves over Italy, regardless of the imaginative names that are attributed to him. The high pressure of the Azores is always part of the same family of subtropical anticyclones, it is the cousin of the African one, but with the difference that it is fed by oceanic air, still warm, but not as warm as the Saharan one. For this reason, when we are dealing with 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, whether 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 once events were decidedly less frequent and lasting than today. Particularly hot summers were also that of 1987, then 1994, but 1998 raised the bar: from that year to today, heat waves have undergone a surge in their frequency. Let’s remember a new bar in 2003 up to the last decade which saw increasingly hot summers with record after record gradually approaching over the years. This does not mean that there are no cooler, unstable phases or summers just above average or on average, such as 2002 and 2014, but there are increasingly sporadic cases, exactly the opposite of what happened before the end of the 90s Wanting to think in metaphors: in the past it happened to everyone to get sick sometimes, but if in recent years we get sick much more frequently, it means that there is something wrong (even if sometimes we are 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 today. The crucial point, however, is the time scales: natural climate cycles occur over millenniawhich also allows for an adequate readjustment of ecosystems. The climate change we are witnessing today is instead extremely rapid and acts on time scales of the order of decades, not millennia: we are all realizing it. And it is at this speed that anthropic forcing takes over, which therefore adds to the natural one, as this acceleration of climate change has occurred since the industrial era. Going back to thinking in metaphors: it is natural that we age, but if suddenly we find ourselves already at 40 with the equivalent of 80 years of age, something is wrong.
THE SIDE OF THE MEDAL OF THE HEAT, VIOLENT THUNDERSTORMS – Warm, humid air is the main fuel for thunderstorms. Clearly in a situation of such intense heat, the phenomena Once developed, storms can manifest themselves with particular violence, having much more energy available, resulting, however, dangerous. This has already happened in the Alps, but in general the North in the next few days will risk very intense storms associated with large hail and sudden violent gusts of wind with potential damage. The price to pay for a partial refresh.
Consult the situation live also through the eye of the geostationary satellites reworked by our team. Here the section >> Satellites.