A lot of Saharan dust is to be expected in the air in Switzerland again, especially during the course of Monday and in the night to Tuesday with an elongated south to south-westerly current. This Saharan dust will be pushed further east on Tuesday or washed out with a cold front moving through. Saharan dust has a variety of effects on people and the environment in Europe, but also worldwide.
Lots of Sahara dust today Monday
As announced, there is a lot of Sahara dust in the air today, Monday, with only the Grisons still spared high concentrations in the morning (see Fig. 1).
Fig. 1: Aerosol (Sahara dust) forecast for Central Europe for this morning; Source: Copernicus Atmosphere Monitoring Service
As a result, the webcams in the west are showing significantly poorer visibility this morning than in the Upper Engadine, for example (see Figs. 2 and 3).
Fig. 2: Webcam La Dôle heute Morgen; Source: roundshot
Fig. 3: Webcam Sils in the Upper Engadine this morning; Source: roundshot
As the day progresses, there will also be more and more Saharan dust in the south-east.
The Saharan dust can also be seen in the PM10 particulate matter values, which are well above the limit value on the Jungfraujoch this morning (see Fig. 4).
Fig. 4: Pollutant levels this morning; Source: Bundesamt für Umelt BAFU
The highest Saharan dust concentrations are expected today (Monday) in the second half of the day and tomorrow night (Tuesday). Tomorrow, Tuesday, a cold front will then push the zone with the high concentrations to the east, with some deposition also taking place(blood rain).
Sequence of the next Sahara dust push
Today, Friday, and until Monday, a southwesterly to early week southerly high-altitude current will bring extremely warm air to Central Europe and thus also to Switzerland (for the weather and the expected (record) temperatures, see yesterday's blog). While there is still little Saharan dust in the air in western and central Europe today, a dust-weakened push over Spain and southwest France and northwest Germany will reach as far north as southern Scandinavia at the weekend (see Fig. 1).
Fig. 1: Aerosol (Sahara dust) forecast for Central Europe for Sunday noon; Source: Copernicus Atmosphere Monitoring Service
Switzerland will hardly be affected by this Saharan dust push at the weekend, with some Saharan dust most likely on Sunday and in the west. This will then change on Monday, when the zone with high Saharan dust concentrations will move further east and increasingly affect Switzerland (see Fig. 2).
Fig. 2: Aerosol (Sahara dust) forecast for Central Europe for Monday afternoon; Source: Copernicus Atmosphere Monitoring Service
This means that the air will become increasingly hazy from west to east on Monday, which will also promote the formation of high clouds. As a result, temperatures could also be slightly lower than calculated by the weather models.
On Tuesday, a cold front will then move from west to east, pushing the Saharan dust to the east and partially washing it out or depositing it here.
Effects on people and the environment in Europe
- Turbidity of the air : Saharan dust is clearly noticeable through clouding of the air. At high concentrations, the air turns yellowish. The sun usually only appears cloudy and as if through a frosted glass (see Fig. 3).
Fig. 3: Milky and pale sunshine with lots of Sahara dust; Source: roundshot Kronberg vom März 2022
- Highly elevated levels of particulate matter, especially at high altitudes: Saharan dust, as the name suggests, consists mainly of dust particles, which in turn consist of around 60% quartz. Concentrations are particularly high at high altitudes. Studies have shown that Saharan dust is significantly less harmful to health than traffic-related particulate matter, for example. Nevertheless, it can lead to increased problems for people with asthma and respiratory problems. It is also suspected, but not yet proven, that pollen becomes more aggressive in combination with Saharan dust.
- Blood rain: Blood rain is the reddish color of rain, which is mainly caused by precipitation with a Saharan dust shower. This blood rain washes the dust out of the air and can cover cars, window panes and garden furniture with a reddish-brown layer (see Fig. 4).
Fig. 4: Precipitated Sahara dust on cars; Source: UBIMET
- Yellowish/brownish snow: If Saharan dust is deposited on snow, it can take on a yellowish to brownish hue during heavy events (see Fig. 5).
Fig. 5: Discolored snow due to Sahara dust last Easter Saturday; Source: roundshot Paradiso St. Moritz
- Increased ice melt and thus increased glacier retreat: If a lot of Saharan dust is deposited on glaciers, this increases the melting of the ice. While around 90% of solar radiation is reflected on ice, dust-covered ice absorbs much more energy, causing it to melt more quickly. Saharan dust had a major impact on the record ice melt on Alpine glaciers the year before last. It could also have an impact this year, as we are already experiencing the second strongest Saharan dust event after Easter. Nevertheless, the amount of snow at high altitudes and thus at the height of the glaciers is currently above average compared to the long-term average (see Fig. 6). However, the situation could change quickly if there are further mild phases in spring like the one at the weekend.
Fig. 6: Current snow depth compared with the long-term average for April 5 (blue tones above average); Source: WSL-Institut für Schnee- und Lawinenforschung SLF
Effects worldwide
- Fertilizer effect: The colourful mixture of quartz sand, clay, goethite, gypsum and fossilized algae (the Sahara was not always a desert) serves as fertilizer. Not so much here, but in a roundabout way almost worldwide. In early summer, for example, the swirling sand and dust is transported by the trade winds across the Atlantic to the Amazon region, where it fertilizes the otherwise rather nutrient-poor rainforest. Without the Sahara, the Amazon rainforest as we know it today would probably not exist! In Europe, the Iberian Peninsula in particular benefits from Saharan dust, as the distance to the Sahara is naturally shorter here and Saharan dust surges are therefore more frequent. In total, the large-scale air currents transport an estimated 500 million tons of Saharan dust across the globe over the course of a year, with around 40 million tons reaching the rainforests of the Amazon.
- Saharan dust inhibits hurricanes: Studies have shown that the veil of Saharan dust reflects and absorbs sunlight, making the sea surface cooler, which deprives the hurricanes that form of the energy they need. When there is a lot of Saharan dust, there are hardly any strong hurricanes.
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