Destructive gusts of wind are at all times, but where do they come from?

The storms were so severe that roofs were blown off, buildings collapsed and trees were uprooted. “Not here as it used to be” Gerrit Janszoon Kooch closed, when on the first of August 1674 the summer storm passed our country. “One does not see a hex on the rock here / There are no trees on the side / And there too I miss a tower.”

That was the infamous storm that swept over the nave of the Dom Church in Utrecht, and it indicates: devastating gusts of wind at all times. All because the air does not go through an orderly arrangement, but quickly becomes subject to the strange physics of turbulence.

As a result, air currents can mix into unexpected gusts of wind and sudden gusts of wind appear seemingly out of nowhere, “like lightning in the sky,” as Koch noted in 1674.

Essentially what happens is that wind flow is affected by differences in speed. There are always such differences: after all, the wind speed on Earth is zero. Because of these differences, the air curls up into eddies of varying intensity and speed. Kelvin Helmholtz instability, Physicists say: a phenomenon that can also be seen in swirls of water or in a smoke plume from a chimney.

In the wind field, these compressions translate into thrusts: over 50kph a gust becomes “bursting”, a gust above 75kph becomes “heavy”, and over 100kph even “very severe”. According to the official definitions.

The fact that wind is accompanied by wind is an established fact, says Dries Allarts, who does research at TU Delft on wind farms, among others. “Wind is a turbulent phenomenon. Such a wind is a kind of spot in the wind stream where the speed is locally higher. A transverse pattern that comes and goes after a few seconds.

Wind flow can be disrupted in several ways. Air vortices can form around buildings, resulting in high winds. Autumn wind is a special case: cold air suddenly blows from an approaching thunderstorm. A local phenomenon, but on Earth the sky is “splattered”, KNMI visually notes.

The result is violent vortices and gusts of wind. Meteorologists use the word disaster akin to disaster movies.Gustenado“to use, abbreviated from words”wind gust(windstorm) and “hurricane”.

And anyone who thinks: good wind power, like this storm, will be disappointed. “I wouldn’t be surprised if no wind power was produced this morning,” says Allaerts. “Above a wind speed of about 23 or 25 meters per second, the turbines are turned off for safety reasons.”

The hardest batch

To measure wind gusts, take the strongest 3 second wind from a 10 minute period. The most powerful windstorm ever measured in our country dates back to 1948. A tornado accidentally hit the KNMI anemometer in Vlieland at a speed of 202 kilometers per hour.

The strongest “normal” wind gust occurred in 1921: 162 kilometers per hour. At the global level, this record is, of course, higher. In 1996, Tropical Storm Olivia recorded wind gusts of 407 kilometers per hour, which is currently the world record.

In 1674 the ruin was colossal. Countless church steeples, buildings, and trees were snapped down, and an unknown number of people were killed. An eyewitness stated that “most of the people accustomed to such a storm groaned and wept: it seemed that the last day was near.” Not good if this summer storm is repeated.