In today’s Academic Minute, Dr. Philip Marcus of the University of California Berkeley explains the persistence of Jupiter’s Great Red Spot.
Philip Marcus is a professor of fluid dynamics at the University of California Berkeley where he heads the Computational Fluid Dynamics Laboratory. His research group is focused on the fluid dynamics of vortices, waves, turbulence, and hydrodynamic stability.
Dr. Philip Marcus -Jupiter's Red Spot
Why do storms on Earth last no more than a month, yet a whirlpool in the atmosphere of Jupiter, known as the Great Red Spot, lasts for centuries?
The Great Red Spot is huge -- 36 times larger than the United States, and its winds, which clock in at 250 miles per hour, surpass those of the most violent hurricane. But, its most baffling property is its multi-century lifetime.
Scientists believe that the Red Spot should have lasted just a few years. It avoids being torn apart because it is sandwiched between layers of cold and hot air. But, those layers should have warmed and cooled their ways to oblivion in only 5 years and taken the Red Spot along with them.
So why is the Red Spot still here?
One explanation is that the Great Red Spot merges with, and absorbs, smaller “spots”. It was thought that by cannibalizing smaller spots, the Red Spot could stay alive indefinitely, but now we know. That diet is too meager.
We recently found a new explanation for the Red Spot’s longevity – it has weak, vertical winds. Like storms on Earth, the vertical winds of the Great Red Spot appear to be negligible; they are hundreds of times smaller than the horizontal winds. Therefore, previous studies ignored them. To our surprise, when we accurately calculated the vertical winds, the Red Spot’s lifetime in our computer models increased from 5 years to 800 years. The vertical winds escaped the Great Red Spot and then threaded through the atmosphere, where they harvested energy from the surrounding air. When the winds returned to the Red Spot, they brought their bounty, and that excess energy sustained the Great Red Spot for centuries.