Expert: The frequency of Saharan sand is higher in the last decade | iRADIO

Saharan sand appeared again over the Czech Republic. Meteorologists estimate that because of it, temperatures may drop and the sky will become cloudy. How long will he be here? And how serious is the situation compared to the one in the Czech Republic at Easter? “The situation, at least at the moment, is not at all dramatic,” Jáchym Brzezina, head of the air quality department at the Czech Hydrometeorological Institute (ČHMÚ), tells iROZHLAS.cz.

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Prague
12:24 p.m April 28, 2024

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Was the Sahara sand unexpected this time?
It wasn’t completely unexpected. In the models, we have that it generally gets here in the spring probably most of the year.

And of course there are different models. There, the problem is not so much estimating the movement of the sand, the model can do that quite well. But it is rather more complicated in our country in that very often the Czech Republic is almost the most remote place where sand can reach.

So it sometimes happens that the model estimates that it will reach us, for example, but it can end up maybe 100 or 200 kilometers from the border. Then the biggest problem is how well the model can estimate at what height the particles will move.

That was the problem last time. The episode that was at the turn of March and April was completely non-standard precisely in how very low the sand moved, how high the concentrations were. At the time, the model estimated it would make landfall, but underestimated it by about eight times.

Is the situation on Sunday better or worse than last time? How would you compare it?
At the moment, if we look at the pollution map, in terms of PM10 particles (of dust particles, editor’s note)so in the whole country the map is blue, which is the very best value as it is.

This means that at the moment the concentrations are on average around twenty micrograms throughout the country, it can be even less, because the blue category is from zero to twenty.

At the turn of the month, we saw values ​​above 250 micrograms, which is more than tenfold. So the situation, at least at the moment, is not dramatic at all.

It has to do with how high the sand dust particles move. If they are higher in the atmosphere, then a person will notice it perhaps as much as an intermediate turbidity in the sky.

Anyone who has, for example, a photovoltaic power plant can recognize this by the reduced output.

But it is not detectable at our measuring stations, which monitor the air approximately two to three meters above the ground, which corresponds to what a person breathes.

More common, but not very common

You said that dust from the Sahara is a fairly common phenomenon in the spring. How often can we expect Saharan sand in the atmosphere?
They are usually units per year, say up to ten cases per year. It is most common in the spring months, then perhaps in the fall. It also happens in October and November. Of course, it can theoretically occur at any time of the year, but it is most common in the spring.

There are studies that show that frequency has been increasing in the last decade or so. They have various hypotheses including that the gradient between pole and equator temperatures is changing. There are also hypotheses claiming that the flow is changing a little in connection with climate change.

But basically the articles agree that these episodes are more frequent recently. So it’s relatively common for Saharan dust to appear here every year, but then again, it’s not every day.

If it is hypothesized to be related to climate change, does this mean we can expect more frequent occurrences of Saharan dust in the future?
No one will probably tell you that right now, because there aren’t many studies on it. It is difficult to examine precisely because the frequency is not very high. In short, there are not many cases on which to analyze it in detail,

Therefore, even scientific articles can differ on why these cases are increasing in the first place. I don’t think anyone would dare to guess what the future will be like.

When will the air clear?

Going back to Sunday, when can we expect the atmosphere to clear of Saharan dust?
According to the most recent predictions, it should be relatively quick. According to one model, it could manifest itself mainly tomorrow. Then again on Tuesday, rather in the western part of the country, so roughly in the Czech Republic. That’s what’s down to earth.

Conversely, dust that moves higher in the atmosphere could be here for a relatively long time. According to the model I’m currently looking at, until Friday. But this model distinguishes between what is moving aloft and what can be detected on the ground.

From measurements on the ground, the model for Sunday shows dust moving higher in the atmosphere. According to the forecast for Monday, it looks like the dust may lessen. This means that some concentrations at ground stations could, for example, increase. The question is how low the dust will be.

So, according to the latest forecast, the dust could be in the atmosphere above us until the end of the work week, with the fact that if it shows up on the ground, then it should be possible on Monday. And maybe it shouldn’t be significant.

But as we saw last time, this modeling is really quite complex. At the turn of March and April, it was possible to predict that there would be an increase in dust, but it was not possible to predict the value.

It is also necessary to take into account that what we had here at the turn of March and April was absolutely exceptional. None of us who were talking with our colleagues had ever encountered it to such an extent, even though we had Saharan sand many times in the Czech Republic.

Katherine Vašíčková

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