with videoWhoever looked up this morning saw a sky full of white streaks in many places in Holland; condensed aircraft steam. ‘Are there so many more flights today than usual?’, people wonder on social media.
Tom van der Meer
‘This makes you think,’ says forester Luc Roosen with a photo of a blue sky full of white streaks over the Kampina nature reserve in Brabant. “Is this the new normal?”
It’s normal, but certainly not new. It happens more often that flight tracks linger for a while, says Johnny Willemsen from Weerplaza. “There’s really a striking number of them today when I look outside,” he says. “But it can happen at any time of the year. It has to do with a cold northerly flow at about ten kilometers high. That’s the area where a lot of planes fly.”
The stripes are called contrails or contras in the aviation world; a portmanteau of condensation and trace. They are caused by airplanes blowing exhaust gases with a lot of water vapor into the cold air at high altitude. Because it is so cold, the gas quickly turns into a solid form: water vapor. So a real cloud.
That we see the tracks so massive today has more to do with the weather than with the amount of aircraft movement. On average, around 20 percent more people fly in the summer than in the winter, and many go on vacation during this period. But even if there were 20 percent fewer tracks, it would still have been a striking phenomenon.
Cold air, clear weather and a sun
It is connected to three factors, explains Willemsen. A cold and damp air current, the sun shining on it and the fact that it is clear. “At the moment there is a northerly air flow at a height of ten kilometres. It is relatively cold. Moist steam from the aircraft engines therefore concentrates and forms a kind of fog bank of ice crystals.”
When the air is warmer and drier, these crystals quickly evaporate again, but due to the favorable temperature and humidity, they remain for a long time today. The morning sun reflecting in the ice crystals ensures that we see the stripes extra well. During the morning the streaks disappeared again.
But hold on… a cold northerly air current? Isn’t there a heat wave coming? “The wind on earth comes from the east,” explains Willemsen. That air is warm, and will probably cause a number of days with more than thirty degrees Celsius. But it is precisely the cold air that makes it a little more pleasant. “It won’t be such a typical heat with sticky nights. It can get quite cold at night.” Despite top temperatures of 25 degrees today and almost 30 degrees tomorrow, it will cool down to 13 degrees tonight.
The weather forecast for the weekend with a preview of the coming days:
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