Satellite view of the Pyrenees on Saturday February 6, 2021. -

Copernicus - European Union - Twitter account

  • After a call to walkers, researchers from Toulouse and Grenoble were able to collect some 200 samples of snow tinted by the famous Saharan cloud.

  • A first estimate assesses the extent of the phenomenon at several tens of thousands of tonnes of dust.

  • Effect on the melting of the snowpack, radioactivity ... The famous samples have not finished being exploited.

An influx of jam jars, freezer bags and plastic boxes of all kinds on bench tops and in laboratory fridges.

Here, in addition to the spectacular images and the peaks of pollution, the other effect produced by the famous cloud of the Sahara which repainted the Alps and the Pyrenees in ocher during the first weekend of February.

Faced with the scale of the phenomenon, and with the aim of quantifying it, the center for spatial studies of the biosphere in Toulouse (Cesbio-CNRS), and laboratories of the National Meteorological Research Center of Grenoble had launched an appeal to mountain people, residents or Sunday walkers, to collect samples.

Mission successful.

The researchers received nearly 200 submissions, Pyrenean or Alpine, French or even Swiss.

The parents of the friends of the colleagues of the researchers mobilized, but not only.

“A lady, who worked at the closed ski lifts, had time.

She sent me three samples, ”says Simon Gascoin, the Toulouse researcher behind the call, who applauds the efforts of amateurs to respect the instructions, to calibrate their samples and therefore allow the phenomenon to be quantified per square meter. .

Challenge observation satellites

If some “cores” of orange sand have been frozen, most have been emptied and filtered to keep only the Saharan content - not really sand strictly speaking but rather dust - and to weigh it.

Verdict of the first episode, the most impressive?

"According to our initial calculations, several tens of thousands of tonnes of dust fell," says Simon Gascoin.

Samples of orange, alpine snow.

- Marie Dumont - Snow Study Center

Analyzes will continue.

At the Grenoble Snow Study Center (CNRM), Marion Réveillet just finished on Wednesday labeling, with colleagues, the last Pyrenean samples.

It is waiting for the precise result of the weight analyzes to run its weather models and assess “the impact of the episode on the melting of the snowpack”.

“We already know that it can be very strong because when the snow is darker, it absorbs more heat, more energy and melts faster,” explains the specialist.

This participatory science experiment, organized at the outset, will also make it possible to challenge Earth observation satellites.

"We are going to check whether they are able to quantify the dust properly", specifies Simon Gascoin.

This will prevent, at the next exotic cloud, sending a horde of walkers.

Finally, samples will also be sent, at their request, to researchers at the French Atomic Energy Commission (CEA), to cross-reference the first data obtained by an association, and for the time being on the basis of a single geographical point, on the worrying presence of radioactive particles in this dust.

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