Tuesday (19 July) it will be hot in the Netherlands. In fact, every summer in Europe we are confronted with more heat waves, according to a worldwide study. That’s how they arise.
The upcoming heat wave. The annual drought in summer. We can no longer escape it. Can we still look forward to a sunny and warm summer day, while deaths in Portugal and Turkey and burn down dozens of football fields of forest due to the heat wave?
Predicting the weather is like watching coffee grounds. But you can look back in time. It turns out that the number of summer heat waves is increasing faster here in Europe than in other areas in the northern hemisphere, such as the United States and China. That researched and proved an international team of scientists early this month.
Sweating carrots: it only gets hotter
The researchers studied daily climate data for the two warmest months in Europe – July and August – over the past 42 years. Because satellite data is available during that period, they were able to analyze how the air moves over our continent and what that does to the temperature. Their conclusion: the increasing heat wave trend is due to a phenomenon they call the ‘double jet stream’.
“In Western Europe, the weather systems usually come from the Atlantic Ocean and therefore have a cooling effect,” says lead author Efi Rousi . “But during a double jet stream, the course of the weather systems changes towards the north, causing prolonged heat waves over Western Europe.”
Wait a minute: what is a jet stream?
Heat wave trends, twin jet streams, the course of weather systems. That’s a lot of scientific jargon. That’s why below an explanation (with many pictures) based on the hot Tuesday that lies ahead.
A jet stream is very strong wind at about 10 kilometers height. We have two major jet streams in the Northern Hemisphere: the polar and the subtropical. These rush like meandering rivers from west to east. And the wind is so strong that the air around it is sucked in. This is how they look today Friday 15 July ) from:
The northerly wind is blowing right over our country. What we noticed today: elongated clouds, a few showers and strong winds. Slightly closer to the ground (at a height of 3 kilometers) you can also clearly see how the wind of the jet stream splits the warm and cold air.
Below you can see the effect of all those high air currents on the temperature on the ground.
The birth of a heat wave
You might notice something else in the animations above: the vortex of wind off the coast of Portugal and Spain. It splits the polar jet stream just off the coast of Western Europe. Part of the wind goes above and part below.
This has two effects: it shields Spain and Portugal from the cold air coming from the Atlantic Ocean and warm air from North Africa is pumped to Europe. The result: heat. If this ‘double jet stream’ remains in the same place for a long time, as the researchers saw, then you get heat waves .
Next week: slowly but surely warmer
Let’s see what the wind is likely to do. And what that means for the temperature in the Netherlands and Europe. Note in the animations below (the dates for Sunday 17 July ) on the shifting of the jet stream and the vortex.
And on tuesday 19 july , according to expectations the hottest summer day for us, the jet stream has been turned in such a way that the warm air passes directly over France and the Netherlands. You also see that it is cooling down in Southwestern Europe at that time, they get cooler air from the ocean again.
Global warming
For example, structural changes in how the wind blows at high altitudes mean that our summers are getting warmer. But what causes the jet stream to change? What creates such a heat pump vortex?
“A possible explanation is the accelerated warming in the far north, especially over land regions such as Siberia, Northern Canada and Alaska,” says researcher Dim Coumou of the KNMI. Those areas warm up faster than the Arctic Ocean. land and sea contribute significantly to the splitting of the jet stream, or, in Coumou’s words, “This is beneficial for the persistence of dual jet streams.”
The live satellite images and models in this article were developed by developer platform nullschool and are freely available to everyone. Do you want to experiment with the data yourself? earth.nullschool.net