A new explanation for Jupiter’s shrinking Great Red Spot

Jupiter’s Great Red Spot — the largest wind storm in the Solar System — is shrinking, and a new study may help explain why.

Located in Jupiter’s southern hemisphere, the Great Red Spot is a swirling reddish-orange oval of high pressure more than 10,000 miles wide. It consistently blows more than 200 miles per hour counterclockwise, making it technically an anticyclone.

And it’s been shrinking for the better part of a century, especially in the last 50 years. While its latitude has remained relatively consistent, its longitudinal extent has shrunk from 40 degrees in the late 1800s to 14 degrees in 2016, when the Juno probe flew by the planet for a series of flybys.

“Many people have looked at the Great Red Spot over the past 200 years and been as fascinated as I was,” said Caleb Keaveney, Ph.D. student at Yale’s Graduate School of Arts and Sciences and lead author of a new study in the journal Icarus.

“A lot of those people weren’t professional astronomers—they were just passionate and curious. That, plus the curiosity I see in people when I talk about my work, makes me feel like I’m part of something bigger than myself.”

Some of the interesting things about the Great Red Spot are related to the many mysteries that surround it, despite the fact that it has been studied extensively. Astronomers do not know exactly when the spot formed, why it was formed, or why it is red.

In the study, Keaveney, who is part of Yale’s Department of Earth & Planetary Sciences, and his co-authors, Gary Lackmann of North Carolina State University and Timothy Dowling of the University of Louisville, focused on the effect of smaller transient storms on the Great Red Spot.

The researchers performed a series of 3D simulations of the site using the Explicit Planetary Isentropic-Coordinate (EPIC) model, an atmospheric model for planetary applications developed by Dowling in the 1990s. Some of them simulated interactions between the Great Red Spot and smaller storms of varying frequency and intensity, while another set of control simulations omitted small storms.

A comparison of the simulations showed that the presence of other storms strengthened the Great Red Spot, causing it to enlarge.

“Using numerical simulations, we found that by feeding the Great Red Spot food from smaller storms like those found on Jupiter, we could modulate its size,” Keaveney said.

In part, the researchers based their modeling on long-lasting high-pressure systems observed closer to home, in Earth’s atmosphere. These systems – known as “heat domes” or “blocks” – regularly occur in the westerly jet streams that circulate in Earth’s mid-latitudes and play a major role in extreme climate events such as heat waves and droughts.

The longevity of these “blocks” has been linked to interactions with smaller, transient weather mechanisms, including high-pressure eddies and anticyclones.

“Our study has compelling implications for meteorological phenomena on Earth,” Keaveney said. “Interactions with nearby weather systems have been shown to maintain and amplify heat domes, motivating our hypothesis that similar interactions on Jupiter could sustain the Great Red Spot. By confirming this hypothesis, we provide further support for this understanding of heat domes on Earth.” “

Keaveney said further modeling will allow researchers to refine the new findings — and perhaps shed light on the initial formation of the Great Red Spot.