Five departments are currently on Heatwave Orange Vigilance, and thirteen are on Storm Yellow Vigilance. According to the Meteo France, the temperature in the southeast will reach 40.1 °C and will begin to drop by the morning of Sunday, 15 August. “Thursday (August 12, 2021, editor’s note), we reached an absolute heat record in Europe with a temperature of 48.8 °C in Syracuse, Sicily, but 50.3 °C in Kairouan in Tunisia.”, said Frédéric Nathan, forecaster of Meteo France, during a press conference.
High pressure and low pressure: between good weather and rain
Why this temperature in the southeast of France? A cluster of warm air has been present in North Africa for weeks. An anticyclone coming from Sicily supported this warm air mass to rise up to the edge of France, close to the Maghreb shores. DThe atmospheric pressure or the weight of the air column is greater in a region of high pressure. The high pressure system acts like a full balloon that is deflated: the air is released from the sides. It is replaced by air from the upper layers of the atmosphere. While going down, the air heats up and dries, inhibiting the development of the precipitating clouds, hence the constant association between high pressure and good weather. This warm air mass can further heat up under air inertia, as in Canada in June, forming a heat dome. opposite of this, A depression will adsorb the ambient air mass. When the air cools during its rise, it blows up and escapes upwards. The water vapor present in it eventually condenses to form clouds and leads to bad weather. Recently the same thing happened in France.
According to Météo France, the heatwave currently present in the southeast of France is significant, but not exceptional, for example compared to June 2019, which reached a temperature record of 46 °C in Hérault. This is a localized heat wave, which will be more and more frequent due to global warming. “On a European scale, France is a slight exception due to the cold drops in July. It has been very hot in South-Eastern Europe, in Greece, in the Balkans, in Bulgaria, in Romania, up to Turkey, but so far we have had a cool summer, even though the month of July was close to normal., says Frederick Nathan. In the week of August 16, temperatures are expected to drop and return below the seasonal average over the northern part of the country. The southern half will be around the seasonal norms and an average of 27°C will mark the end of this scorching event.
The dome of a drop of heat and cold: nature hates imbalance
Christophe Cassou, climatologist, lead author of the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) and director of research at CNRS, declared science and the future She “Climate change increases the incidence and intensity of these extreme events, whether it is torrential rains or, conversely, heat waves and droughts, as global warming is deeply disrupting the entire water cycle. “
At temperate latitudes, these heat waves or flood events are linked to atmospheric circulation. There is a western wind tube called a jet stream, like a river that circles the planet and is found at an altitude of about 10-12 km. This “river” is turbulent and can form spontaneously, trapping small ridges that spin for a while and then dissipate. These meanders and eddies are responsible for extreme summer events at temperate latitudes. When the jet stream is bent and trapped in this position, this condition leads to the development of a stable heat dome. “Nature hates imbalance and if there is a dome, there is also a cold drop.“, specifies Christophe Cassou. A cold drop is a cold hole, with fresh air at its height, so unstable air causes thunderstorms. They were responsible for floods in Belgium and Germany in July. Today, cold droplets are less cold than in the past due to global warming but they contain more water, which explains the higher intensity of rainfall.
According to the latest report from Group 1 of the IPCC, reducing our greenhouse gas emissions over the next ten years will reduce the occurrence of these extreme climate events. At the same time, bringing vegetation back to the city will refresh and restore the ecosystem, giving a dimension to the flood management infrastructure to promote resilience in the face of these events.
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