the return of the tinted sky! Forecasts, duration … Info


SAHARA SAND. On Monday, April 11, the French sky suddenly turned yellow and a thin layer of ocher dust covered the cars. This is the new wave of sand coming from the Sahara, almost a month after the one that passed over our heads in March.

Rebel! On April 10, a month after the wave in March, sand from the Sahara flew up and covered the sky in France with an orange hue with deposits due to the passage of precipitation. First very visible in the Pyrenees, where the ocher dust crossed the mountainous relief, the phenomenon will gradually go up France in the coming days, first towards the “west of the great east”, according to the experts. The concentration will intensify on April 12, until the dust cloud covers “the whole of France”, especially on a band going from “Occitanie to Normandy and Hauts-de-France”, Météo -France explains. Last month, the Pyrenees-Atlantiques were the most affected area, according to the Central Air Quality Monitoring Laboratory. This time, the meteorological phenomenon was to leave traces on the cars with a thin layer of dust, but also in the air with radioactive particles. How do you explain this strange phenomenon?

The orange sky that the French can observe around April 11 and 12 is actually associated with an influx of sand from the Sahara. This meteorological phenomenon, if impressive, is quite common: Météo-Paris indicates that it occurs several times a year, or even every season depending on the period. It should be noted that the intensity of the phenomenon in March last year is linked to the period when winter is its preferred season, as the atmospheric circulation there acquires a very marked meridian component. This time it should be less intense, but similar to the previous ones. In France and Spain, it even has nicknames: sirocco and calima, respectively. It occurs when an Atlantic depression dives south and settles over the Iberian Peninsula, raising a strong warm wind from south to southeast over the Maghreb. If the wind is sufficiently sustained between this sector and France, it produces a “pumping phenomenon”: this dust directly reaches our territory and can lead to precipitation.

It is at this point that we observe deposits on the earth and a change in the colors of the sky. This time, the depression is particularly important: a depression off the Atlantic Ocean connected by a thalweg induces winds from the southern sector, bringing desert dust back from the northern part of the Maghreb, details Meteo France. For orientation, a thalweg corresponds to the line formed by the points that have the lowest elevation, either in a valley or at the bottom of a stream.

The wind strength, the geographical extent and the duration of the phenomenon make it an event, despite the frequency of this type of event in France. This south-to-southeast current, dynamic enough to send sand dust to our countries, first spread large amounts of sand dust to southwestern Spain on April 7th. But according to David Minguet, forecasts at MétéoFrance: “This episode will be less intense than the previous one. This Monday, April 11, there is already some desert dust, in fairly low concentration, arriving from the Pyrenees in the south of the country. East.” (comments reported by France 3). You are reassured: This time, the sand in the desert will not be as tenacious as encapsulating your car.

When was France hit by these deposits? On the evening of April 9, a cloudy episode filled with dust from the Sahara in France erupted. These sand dusts are currently extending north. David Minguet also clarified that these concentrations will “intensify this Tuesday, April 12” and that the cloud will spread across France, “especially with a band spreading from north to south”. Higher concentrations are expected to remain in the southwest before flowing out through the German borders.

This April 12, but especially April 13, Parisians will observe dry and wet deposits in the streets of the capital, a little after the French regions further south, which were hit by the 10th Guillaume Séchet, from Météo Villes explained precisely to the newspaper Le Parisien , that the massive phenomenon, when it reaches Paris, will make its sky “very milky, a little phosphorescent, before it manages under the influence of the north-easterly winds”. Note that especially in Paris the temperatures are higher! Compared to the 12 degrees that the Parisians suffered in the first week of April, the 21 degrees that this cloud brings will change the situation.

Significant dust concentrations in the west, especially in the southwest, which were first hit on Saturday, April 9, moved toward Aquitaine. It is expected that the cloud on Wednesday 13 April will “shift slightly towards the eastern part of the country” with a “strengthening of concentrations” expected in “Western Occitan”, specifies MétéoFrance. Last time, in March, experts had noted a deterioration in the Atmo air quality indices in the region’s departments. The prefect of the Pyrénées-Atlantiques had even triggered the warning procedure for fine particle pollution in those two days.

The peak will be reached in the northern half of France on Wednesday 13 April … the day when all the French regions will be flooded with sand from the Sahara and where deposits were visible on the bodies of vehicles. The normalization was to come on Thursday, April 14, when the cloud begins to evacuate via the southeast axis, with a change in the meteorological situation via a “ridge”, which is set up on the “Atlantic facade”.

However, the dust that this phenomenon spreads is harmful (because it contributes to the increase in the level of fine particles), it is recommended to wear a mask when traveling outdoors, especially for people with respiratory problems. . But is there radioactivity in this phenomenon? In fact, experts agree that the fallout from nuclear tests carried out in the 1960s left a lasting mark on the Sahara desert, as the Institute for Radiation Protection and Nuclear Safety reminds us. These falls come from hundreds of atmospheric tests carried out by several great powers: in the end result, the USSR and the United States are neck and neck with 219 shots, followed by Britain with 23 shots, China with 22 and France with only 4 in the Sahara (but 46 in Polynesia).

The sand contains cesium 137, a radioactive element that has a half-life of 30 years and can therefore act on these particles. However, radioactivity specialists want to be reassuring, as the phenomenon had already occurred in February 2021, without it having major consequences for air quality. Indeed, if the activity concentrations of cesium 137 during this February month had been higher than the average of the activities measured in February 2019 and 2020 (measurements made by the IRSN as part of its mission to monitor airborne radioactivity), the concentration of cesium 137 to present in the fine particles of sand from the Sahara was “in February 2021 extremely low in the atmosphere and on the earth’s surface” remembers Jean-Christophe Gariel, Deputy Director General of Health and Environment at IRSN (comments reported by Le Parisien). The health impact of these meteorological episodes is therefore considered negligible by the IRSN. If there are health risks, they are no worse than with classical air pollution: Like in March, Météo-France did not communicate an operating color forecast, because this phenomenon will not normally have any real impact on human safety.

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