The Sahara dust returns to Switzerland – and brings with it stunning effects

Suddenly everything is yellow and clouds gather in the sky, in the worst case it even rains “blood”. What seems to be the beginning of the apocalypse is in fact a weather phenomenon that we experience several times a year in Switzerland: Saharan dust.

At the moment, the dust particles have just reached southern Europe. According to forecasts from the EU Atmosphere Service Copernicus, the red-orange wall should also roll over Switzerland by the end of the week. But what does this weather situation mean? And is it even dangerous? Here are the most important things you need to know about the weather phenomenon:

Let’s start with the basics: the dust comes from the African Sahara desert. Here, wind, erosion and chemical weathering break rock into smaller and smaller pieces – the dust is created. Depending on the type of weathering, the minerals are left behind. The Sahara dust carries a lot of calcium and magnesium and is therefore also called mineral dust. When these particles end up in the air, they are called aerosols or particulate matter.

When the soil in the Sahara desert heats up, thermal turbulence is created, propelling the dust particles several thousand meters into the air. In the meantime, if the ground cools down, a layer of air is created through which the aerosols can no longer pass. If there is no wind, the particles can remain at this height as aerosols for several months.

However, often the Sahara dust is spread in almost all parts of the world. A large part reaches South America via the trade winds. However, for the dust to reach us in the north, a certain weather situation must exist: when a low-pressure area forms over the Mediterranean, cold air flows from Europe to Africa at low altitude, while warm air accumulates dust. particles move to Europe at higher altitudes.

This leads to a dust event in the Sahara and the sky over Switzerland turns yellow to red. In Switzerland, these events have been measured since 2001 by a MeteoSwiss measuring station on the Jungfraujoch in the Bernese Oberland. They are most common in spring or fall, even when Mediterranean lows are particularly common.

The MeteoSwiss dataset shows that half of the dust events in the Sahara have dissipated after just a few hours. Only about a quarter of an hour lasts longer than a day. Between 10 and 35 events are measured annually on the Jungfraujoch.

If precipitation falls during dust events in the Sahara, it is colloquially referred to as blood rain. This is because the iron-rich aerosols leave rust-brown deposits. In the 19th century people thought that there was a permanent layer of dust in the atmosphere, but now we know that the deposits come from dust from the Sahara.

The Sahara dust increases the amount of particles over Switzerland. This keeps temperatures low despite the warmer air. The reason is that the particles reflect part of the sun’s rays and the amount of radiation is therefore lower. In addition, water condenses on the mineral dust particles, especially at high altitudes. This leads to more cloud formation.

It’s hard to believe, but: Saharan dust is the main nutrient supplier for the Amazon rainforest. Providing the forests with minerals is like natural fertilizer. In addition, researchers suspect that the Sahara dust contributes more to temperature fluctuations than previously thought.

However, the mineral dust could also play a role in the formation of hurricanes over the Atlantic Ocean. Meteorologists now believe that the particles affect how strong a hurricane is.

Dust events in Switzerland’s Sahara even lead to more air pollution. Preventing fine dust particles in the air is an additional burden, especially for allergy sufferers. However, in smaller concentrations, Saharan dust does not damage the health of healthy people.