Jupiter, full of chaotic clouds and raging with violent winds, is famous and loved for its gloriously stormy atmosphere. Since the Juno spacecraft arrived there in 2016, we’ve had unprecedented access that has helped us understand what drives the gas giant’s crazy weather.
But Juno did not only provide answers, but other questions as well. Until the Juno mission, we had not been able to observe Jupiter’s poles well. What the spacecraft saw was a jaw-dropping: polygonal arrangements of storms both north and south, surrounding a storm in the center.
At Jupiter’s north pole, nine cyclones rage, one in the center, and eight others arranged neatly around it, all rotating counterclockwise.
At the south pole, Juno spotted six storms in 201
Since 2016, these massive storms – comparable in size to the continental United States – have persisted, not melted. And now, as set out in a new paper, we may finally have an idea why.
Jupiter’s arrangement is different from that of the other gas giant in the Solar System, Saturn, which has only a single, huge storm at each of its poles. It is also different from processes on Earth: on our planet, most cyclones form in tropical latitudes and move towards the poles, but they dissipate on the earth and cold ocean areas before they get there.
Since Jupiter has neither land nor cold oceans, it makes sense that its storms behave differently than Earth, but the question remains: why don’t they merge to create single storms a la Saturn?
Astronomer Cheng Li of the University of California, Berkeley and his colleagues at Caltech performed numerical simulations of storm patterns and discovered a number of conditions in which storms can remain discrete and stable for extended periods of time without kissing together in a mega storm.
It is basically a “goldilocks zone” for Jovian storms.
‘We find that the stability of the model depends primarily on shielding – an anticyclone ring around each cyclone – but also on depth,’ the researchers wrote in their paper.
“Insufficient shielding and shallow depth lead to melting and loss of the polygon pattern. Too much shielding causes the cyclonic and anticyclonic parts of the vortices to drift apart. Stable polygons exist in between.”
The team used equations that describe the movement of a single layer of fluid on a sphere and modeled the polygonal arrangements of the vortices. This is nothing new, but the team added polar geometry and beta drift – the tendency of cyclones to move due to an increase in Coriolis force with latitude due to wind speed – into their models, for an understanding. more detailed of the dynamics at play on Jupiter.
According to their findings, there are two things at stake and the conditions for both must be right. The first is, to a lesser extent, the depth of the cyclone – how far it goes into the Jovian atmosphere. Too shallow and the storms will merge.
But the biggest influence on the adhesion power of storms is a phenomenon known as vortex shielding. This is when the vortex – in this case, our Jovian cyclones – is surrounded by a ring moving in the opposite direction. Hence, each of the counterclockwise cyclones on the north pole is surrounded by a powerful wind blowing around the cyclone in a clockwise direction.
If this shielding is too weak, the storms will merge. If it is too powerful, the storm and its shield will pull away from each other, causing total disaster. So, to persist, both the depth of the cyclones and the strength of their swirling shields must be right.
And then, another series of mysteries.
“There are a lot of questions that we haven’t answered,” the researchers wrote.
“We have not explored how cyclones form, whether they form on the spot or move upward from lower latitudes. We also have not explained how a steady state is maintained, because the number of cyclones does not increase with time. Furthermore, we have not determined how the shielding develops, or why only the Jovian eddies are protected. “
The team has yet to test their models on Juno’s actual data. This, however, could lead us to some answers to these deeply intriguing questions.
The research was published in Proceedings of the National Academy of Sciences.