It is the iris of Jupiter’s great eyeball, rotating to gaze menacingly at the cosmos: the Great Red Spot, the largest and longest-lived storm in the entire solar system.
Humanity has been observing it for centuries, it is a colossal anticyclone currently a little larger than the Earth, with winds blowing counterclockwise at speeds of up to 680 kilometers per hour.
As powerful as its rage is, however, the Great Red Spot has diminished considerably since the first accurate records of its existence in 1831. The storm was once much stronger; over time it has diminished, and it continues to diminish.
Scientists now think they understand why: the Great Red Spot feeds on other, smaller storms that mix with it. If it were not for these small storms which the Great Red Spot could devour and swallow up, it would be unable to maintain its prodigious dimensions.
“Many people have looked at the Great Red Spot over the past 200 years and have been as fascinated by it as I am,” says Caleb Keaveney, a PhD in astronomy at Yale University.
“We discovered through numerical simulations that by feeding the Great Red Spot with a regime of smaller storms, as occurs on Jupiter, we could modulate its size.”
At the end of the 19th century, the Great Red Spot was 39,000 kilometres wide. Today, it is just over a third of that width, or 14,000 kilometres. The diameter of the Earth, just over 12,742 kilometres, could still fit inside, but the volume is getting smaller and smaller. We have never seen the Spot this (relatively) small.
Scientists are studying this strange phenomenon, but it remains mysterious. Jupiter is very different from Earth, and its climate is much more capricious. Despite these differences, fluids, such as atmospheric gases, behave in certain ways that can be studied using the mathematics of fluid dynamics.
While we can’t exactly extrapolate how Earth’s climate will behave on Jupiter, we can use our understanding of Earth’s atmospheric processes to try to figure out what’s happening on Jupiter. That’s what Keaveney and his colleagues have done.
We know from research published in 2021 that Jupiter’s Great Red Spot effectively “eats” the small storms it encounters, growing larger in the process. So the researchers used a similar phenomenon observed here on Earth to inform their models of Jupiter’s atmosphere.
In jet streams that flow through Earth’s atmosphere, long-lasting high-pressure systems called heat domes or heat blocks can form where the jet stream slows to a halt. These blocks can play an important role in heat waves and droughts because they trap warm temperatures below them for long periods.
The longevity of these blocks has been linked to anticyclones and other smaller weather phenomena. Using this information, the researchers created a model of Jupiter’s atmosphere and the Great Red Spot, simulating the interactions between the storms.
They found that when a smaller storm encountered the Great Red Spot, the former storm maintained its size, or grew, compared to simulations without these interactions. And the degree to which the Spot was maintained was stronger if there were more interactions. Finally, the strength of the smaller storm also played a role. A stronger storm gave the Great Red Spot a bigger boost.
There’s nothing we can do about the Great Red Spot. Jupiter is headed toward Jupe, we’re just here to enjoy the show. But learning more about its amazing atmosphere can help us better understand how the climate works on our own planet, which is pretty cool.
“Our study has compelling implications for weather events on Earth,” Keaveney says.
“Interactions with nearby weather systems have been shown to sustain and amplify heat domes, which motivated our hypothesis that similar interactions on Jupiter could sustain the Great Red Spot. By validating this hypothesis, we provide further support for this understanding of heat domes on Earth.”
The research was published in Icarus.
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