Predicting hurricanes, warning about earthquakes, controlling global atmospheric phenomena - this is the dream of modern science, which studies the complexes of causes underlying an event. Hurricane wind is one of the areas of research in atmospheric physics, which has been quite successfully predicting the trajectories of vortices for many years, but still cannot predict their strength, and therefore the scale of possible destruction.
For 20 years now, research has been hovering around the "hurricane equation", which is derived from our understanding of the mechanism of its formation. Let's say a hurricane forms over the ocean. This was due to the convective rise of warm and humid air, condensation of water vapor with the release of latent heat of vaporization. But if we set the necessary numbers instead of variables, we in no way get such a high wind speed that can be observed in reality.
It is well known that the more wind, the more waves on the water surface. Waves are a natural "roughness" that creates the force of friction between the wind and the surface. If we consider the balance between the energy input and its absorption due to friction, it turns out that the stronger the wind, the larger this absorption will be. That is, the waves should "extinguish" the wind, but in reality this does not happen.
Whirlwind over Hamburg. June 7, 2016 / AP Photo / DPA / Monika Zucker
In the late 90s, American researcher Kerry Emanuel put forward a "crazy" hypothesis that did not find any response in scientific circles. He suggested that friction decreases, and the resistance of the ocean surface, on the contrary, decreases with increasing wind. But this cannot be?
Then, in 2003, an article was published in the journal Nature describing a similar phenomenon. Since the late 1990s, the US National Oceanic and Atmospheric Administration's Hurricane Observing Center has been regularly conducting field measurements of wind speed inside tropical cyclones using falling GPS probes. Based on the generalization of the results of these measurements, it was also shown that the coefficient of resistance of the sea surface is significantly lower than the value obtained by extrapolating the measurement data under "normal" winds.
Then the employees of the Department of Nonlinear Geophysical Processes of the Institute of Applied Physics of the Russian Academy of Sciences from Nizhny Novgorod joined in the understanding of this problem.
Institute of Applied Physics RAS in Nizhny Novgorod / Photo: Public domain
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“Our idea was simple: let's repeat these experiments in the laboratory. Let's create a "slice" of the hurricane and see what happens to the water surface. Moreover, there is where! " - said Yulia Troitskaya, Doctor of Physical and Mathematical Sciences, Head of the Department of Nonlinear Geophysical Processes.
She explained that the institute has a unique installation, the "Complex of large-scale geophysical stands", which includes a thermostratified basin with a high-speed wind-wave channel. This complex is included in the register of installations of national importance in Russia.
USU "Complex of large-scale geophysical stands" (KKGS) / Federal Research Center Institute of Applied Physics of the Russian Academy of Sciences
Experiments on hurricane modeling carried out at the Nizhny Novgorod Institute of Applied Physics have produced amazing results. With the help of a high-speed Japanese video camera with a shooting speed of up to half a million frames per second, it was possible to record the processes that gave an understanding of the basics of the formation of a strong wind during a hurricane. It became clear that indeed there is a "smoothing" of the waves, which leads to a decrease in friction and resistance. It was possible to prove a fact that was impossible to believe.
Formation and detachment of drops during hurricane winds / Institute of Applied Physics RAS (Nizhny Novgorod)
In addition, the scientists realized that the "smoothing" effect is not even that important for the formation of strong winds compared to the effective mechanism of splashing.
Yulia Troitskaya explains: “We were interested to know: how exactly does this 'smoothing' take place? How does the wind blow off the ridges? And suddenly, in slow motion, we saw a certain "sail", inflating into a kind of bubble, which bursts, forming a lot of splashes. In studies related to liquid fragmentation, such “sails” have already been discovered, as scientists actively studied the mechanism of liquid fuel injection into internal combustion engines. In English literature, this effect is called a bag breakup - "torn bag". In our scientific literature, it is sometimes called "parachute type" fragmentation.
The process of formation of drops in hurricane winds / Illustration by RIA Novosti. A. Polyanina
Scientists counted the droplets and realized that the most efficient mechanism for generating splashes was found, which greatly changes the picture of the occurrence of hurricanes. Previously, it was believed that splashes are formed at the rupture of floating bubbles and their amount is incommensurably less. It turned out that if we recalculate the results of the Nizhny Novgorod laboratory experiment for natural conditions, then the formation of such strong hurricane winds becomes more understandable. Scientists have realized that it is an effective mechanism for the flow of energy into hurricane winds, so it will soon be possible to predict the destructive capacity of one or another hurricane.
Anna Urmantseva
