Why the great red spot of Jupiter will not die


“Getting involved in reading is a mistake,” Philip Marcus, a computational physicist and professor of mechanical engineering at the University of California at Berkeley, tells me over a cup of coffee at a coffee shop near the campus. “You learn too much. That is how I got hooked on the dynamics of fluids. ”

And it was in 1978, when Marcus worked for the first year as a PhD in Cornell, specializing in numerical simulations of solar convection using spectral methods. But he wanted to study the evolution of the cosmos and the general theory of relativity; the problem, he said, was that people argued that they had never seen the results of the work of the UTO in their entire life. As a result, “this area has calmed down a bit, and all GR specialists dispersed to other areas”.

It was in 1978 that Voyager 1 began to send pictures of Jupiter taken at close range to Earth. When Marcus needed, as he says, “to relax, relieve tension, and all that,” he went to a special laboratory located near the building of astrophysics and admired photos of the Big Red Spot made from Voyager. The storm has already passed hundreds of millions of miles, at least since 1665, when Robert Hook first saw him. “I realized that almost no one in the field of astronomy was aware of the dynamics of fluids, but I was,” he told me. “And I said, well, I have the opportunity to study this issue, and it’s no worse than the others.”

So he has not stopped since. Today he is an expert on the most famous storm in the solar system. Possessing a mountain biker's physique, he answers my questions, actively moving, and sometimes waving his arms in an attempt to refine his words. He admitted that his vitality could lead to clumsiness. “People are suspicious of me,” he says. “If I enter the laboratory, I immediately break something.” Fortunately, according to him, “I was very lucky to be friends with several experimenters.”

What strikes you in the big red spot?

A few things. People have long thought about why the Big Red Spot (BKP) lives so long? The OPF is a storm, and we are accustomed to earthly storms. The average hurricane lives a maximum of a couple of weeks, and the mechanism for its destruction is quite definite: it either passes over cold water and loses energy, or passes over land and abruptly loses energy. Tornado - impressive thing, but she lives only a few hours. So why does BKP live so long? People used to say: "These are clouds that linger at the top of a mountain." Or: "This is an iceberg in a sea of ​​hydrogen." Similar theories ended at once in 1979, when Voyagers 1 and 2 flew past the planet. No one then knew that it was a whirlwind, a huge hurricane, which took six days to turn. The United States would fit in the OPF a couple of hundred times. It really is huge. One of the great accomplishments of the Voyager missions was that they took hundreds of photographs of the clouds that make up the OPF, and we were finally able to see how this thing was spinning, and then we were able to say with confidence that it was a whirlwind. Before that, nobody knew that it was spinning.

How did the BKP appear?

The OPF probably appeared in one of two ways. This could be an upward flow of gas that reached the stratosphere and turned around, which is why the whirlwind turned out. If the ascending stream can reach a sufficiently stable layer of the atmosphere, it can spread horizontally, and when such a stream spreads horizontally on such a rapidly rotating system as Jupiter, this propagation leads to the formation of a vortex. Another possibility is that the jet flow in the atmosphere lost stability, wave oscillations began, and when the amplitude of the wave increased to a certain limit, it broke up, forming small vortices, which then merged.

Why did it appear on Jupiter, and not somewhere else?

On Earth, if you fly over the ocean, you can almost exactly say in which places beneath you will be islands, because clouds will hang over them - topographic features often attract clouds to themselves. But on Jupiter there is no hard surface, unless you go down to a very small nucleus. This is, in essence, a ball of fluid. There is no heating difference between continents and islands. Winds are not interrupted by mountain ranges. All this is not there, so there is a set of very well-organized jet streams on it. And if you have such currents, then whirlwinds appear naturally. Winds go in opposite directions, rub against each other. This is about as a bearing ball, located between two walls, moving in opposite directions. The walls make the ball rotate, and the oppositely moving currents on Jupiter cause the air between them to rotate. The vortices formed between the currents resist everything that runs into them. If I make a whirlpool in the bathroom and slap on it, it will disappear. If I make a simulation of the OPF on Jupiter, located between the zonal winds, and slap on it, trying to divide it into two parts, it will assemble again. Therefore, I imagine jet streams as gardens in which you can grow vortices.

And what physically does not allow the BKP to break up?

I think that the OPF in height is 50-70 km. It has about 26,000 km across. It turns out such a pancake. Just like with a tube of toothpaste, if I put pressure on the pancake in the center, then something will come out from its sides, as well as from the top and bottom. It is known that in the center of the OPT there is a high pressure, but its gases do not crawl horizontally from all sides due to the Coriolis force - they crawl out vertically from above and below. So what prevents the gases from getting out from above and below? I know only one way to prevent this. On top of the OPF there is a dense cold atmosphere cover. It is this additional density that pushes the BKP gases back down. And under the BKP there should be a warm floating atmospheric bottom, which prevents high pressure in the center from pushing the gases down from the BKP. This is a balance.

You can make numerical and analytical calculations and think: “Hmm, I wonder, but how tight is the cover needed? What kind of buoyancy should the bottom have in order to achieve such a balance? ”Kinetic energy is associated with the vortex winds, and potential energy is associated with the cold dense lid on the top and a floating warm bottom. Most of my colleagues who study BKP concentrate on kinetic energy, but I tell them: “No, no, guys, only 16% of energy is concentrated in it”. Most of the OPF energy is the potential energy of a dense cold cover and a warm floating bottom. If you want to stay up at night, thinking about what the BKP can attack, then think about what can attack its potential energy.


Why doesn't the OPF disintegrate from friction?

Our intuition tells us that whirlwinds are not eternal, that they always break up due to some kind of friction. Friction is different, and one of the reasons that could destroy the BKP, according to people, will be Rossby waves . Rossby waves are one of the types of atmospheric waves that exist because the atmosphere is a rotating spherical shell, not a rotating plane. They are often found in the atmosphere, and move at low speed. People thought that the BKP would begin to radiate Rossby waves, which would take away his energy. When unexpected incidents occur in the atmosphere, for example, two eddies collide, as a result, Rossby waves appear. But usually after the formation of a whirlwind, he finishes emitting Rossby waves, so there is no evidence that the radiation of Rossby waves will destroy the BKP, which is in a quasi-equilibrium state.

What else can stop him?

If you begin to study the question of what the BKP can attack and destroy it, you will have to think not only about the influence on the kinetic energy of such factors as friction; you have to think about what is more important - what is attacking potential energy. There is a well-known reason for the potential leakage of potential energy - it is called " radiant equilibrium ". If I could cool one part of the earth's atmosphere, I could get a stopwatch and say: “So, I wonder how much time this area will heat up again and enter into radiant equilibrium with the surrounding atmosphere?” Or, if I did somewhere small the hot section, I could ask: “How long will it take to establish equilibrium due to the transfer of photons and everything else, after which my section will lose its temperature differences?” From the calculations of other scientists it is known that in the place of the atmosphere where the BKP is located, cold or hot the plots disappear in about four and a half years - this time is required for particularly warm or cold patches to become completely indistinguishable from the environment. So we made a lot of numerical simulations, and if we introduce the effect of warming or cooling into our computer model, it turns out that the OPF resolves in four and a half years.

And what feeds him?

The average speed of movement around this spot is about three hundred kilometers per hour. Jet streams also move at about the same speed. But their vertical speeds are considered very small. They are likely to be in the order of centimeters per hour, and therefore they are usually neglected. But in large parts of the atmosphere vertical winds constantly appear, and therefore we think that they cannot be written off. We think that the BKP is trying to destroy the heat transferred to the cold cover and from the warm bottom, and trying to establish radiant equilibrium. But we believe that the BKP manages to survive, despite this radiant heat transfer, because its vertical speed is very small.

Practically it can be considered that when the wind goes down, it becomes warmer, and when it rises, it cools. Thermal radiation of photons inside the BKP is trying to equalize the temperature of its cover and bottom with the temperature of the surrounding atmosphere. This should make the cold tight lid warmer, and it should eventually disappear, which will destroy the BKP.

But at the beginning of the dispersion of the OPT the pressure balance is lost. The loss of balance allows high pressure in the center of the BKP to push the gases vertically through a weakened cap. When lifting, the wind cools, which supplies the lid with new cold air, as a result it cools and becomes heavier. Approximately the same process occurs at the bottom of the BKP, and it restores the warm bottom, which is trying to destroy thermal radiation.

Plus, the gas moving vertically upwards, passing through the vanishing lid, goes outside the OPF and eventually stops rising, and flattens it horizontally in an area many times larger than the OPF area. Then he stops moving out and goes down. This descending gas pushes the atoms and molecules of the atmosphere surrounding the BKP down, reducing their potential energy. As a result, the gas ends its journey, returning to the OPF center. On the way home, gas collects potential energy released from the atmosphere surrounding the OPF.

Collecting this energy balances the loss of BKP energy through thermal radiation. In a computer simulation, you can measure the direction and power of all energies going in and out of the OPF, and the whole energy budget fits in perfectly. There is a large leakage of potential energy into the atmosphere surrounding the BKP due to the circulation of gas, but there is nothing to worry about, because the Sun restores the radiant equilibrium in this place and gives additional energy. So in the end it turns out that the sun serves as a source of energy that prevents the disappearance of the OPF.

What is the value of studying the atmosphere of a distant planet?

If you do not understand how Jupiter works in our own solar system, how can you understand how jupiter works around other suns? Now it is very fashionable to look for other Jupiters in other solar systems, since we are wondering whether there are other planets and whether life can exist on them. The study of the planets that revolve around other suns, you need to start somewhere, you need to make stupid mistakes. That is how the scientific field of research develops.

And now - the complaint. NASA is an excellent organization, and I am grateful to her for the funding allocated to me and my theoretical colleagues. But the amount of money we spend on equipment - in order to send instruments into space, compared to the amount of money we spend on analyzing data from those same instruments, is very unbalanced. Huge amounts of data were received from the Voyagers 31 years ago, and they have not been processed yet. To obtain funding for their processing is extremely difficult. Usually everyone says: “You need to do something new and interesting, with new data! No need to go back to the past and mess with old data! ”But there is a lot of everything in there too! But give Congress only the equipment.

Everyone loves equipment. And what NASA needs is another Carl Sagan. Karl had a talent to persuade people to respect our discoveries themselves, and not just the machines that made these discoveries possible.

Source: https://habr.com/ru/post/405915/

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