Solving the strange storms on Jupiter

Date:
September 24, 2020
Source:
California Institute of Technology
Summary:
Geometric storm patterns on Jupiter's south pole have been a mystery
to scientists, but researchers may have uncovered how they form.



FULL STORY ==========================================================================
At the south pole of Jupiter lurks a striking sight -- even for a gas
giant planet covered in colorful bands that sports a red spot larger
than the earth.

Down near the south pole of the planet, mostly hidden from the prying eyes
of humans, is a collection of swirling storms arranged in an unusually geometric pattern.


========================================================================== Since they were first spotted by NASA's Juno space probe in 2019, the
storms have presented something of a mystery to scientists. The storms
are analogous to hurricanes on Earth. However, on our planet, hurricanes
do not gather themselves at the poles and twirl around each other in
the shape of a pentagon or hexagon, as do Jupiter's curious storms.

Now, a research team working in the lab of Andy Ingersoll, Caltech
professor of planetary science, has discovered why Jupiter's storms
behave so strangely.

They did so using math derived from a proof written by Lord Kelvin,
a British mathematical physicist and engineer, nearly 150 years ago.

Ingersoll, who was a member of the Juno team, says Jupiter's storms are remarkably similar to the ones that lash the East Coast of the United
States every summer and fall, just on a much larger scale.

"If you went below the cloud tops, you would probably find liquid water
rain drops, hail, and snow," he says. "The winds would be hurricane-force winds.

Hurricanes on Earth are a good analog of the individual vortices within
these arrangements we see on Jupiter, but there is nothing so stunningly beautiful here." As on Earth, Jupiter's storms tend to form closer to the equator and then drift toward the poles. However, Earth's hurricanes and typhoons dissipate before they venture too far from the equator. Jupiter's
just keep going until they reach the poles.



==========================================================================
"The difference is that on the earth hurricanes run out of warm water
and they run into continents," Ingersoll says. Jupiter has no land, "so
there's much less friction because there's nothing to rub against. There's
just more gas under the clouds. Jupiter also has heat left over from
its formation that is comparable to the heat it gets from the sun, so
the temperature difference between its equator and its poles is not as
great as it is on Earth." However, Ingersoll says, this explanation still
does not account for the behavior of the storms once they reach Jupiter's
south pole, which is unusual even compared to other gas giants. Saturn,
which is also a gas giant, has one enormous storm at each of its poles,
rather than a geometrically arranged collection of storms.

The answer to the mystery of why Jupiter has these geometric formations
and other planets do not, Ingersoll and his colleagues discovered,
could be found in the past, specifically in work conducted in 1878 by
Alfred Mayer, an American physicist and Lord Kelvin. Mayer had placed
floating circular magnets in a pool of water and observed that they
would spontaneously arrange themselves into geometric configurations,
similar to those seen on Jupiter, with shapes that depended on the number
of magnets. Kelvin used Mayer's observations to develop a mathematical
model to explain the magnets' behavior.

"Back in the 19th century, people were thinking about how spinning
pieces of fluid would arrange themselves into polygons," Ingersoll
says. "Although there were lots of laboratory studies of these fluid
polygons, no one had thought of applying that to a planetary surface."
To do so, the research team used a set of equations known as the
shallow-water equations to build a computer model of what might be
happening on Jupiter, and began to run simulations.

"We wanted to explore the combination of parameters that makes these
cyclones stable," says Cheng Li (Phd '17), lead author and 51 Pegasi
b postdoctoral fellow at UC Berkeley. "There are established theories
that predict that cyclones tend to merge at the pole due to the rotation
of the planet and so we found in the initial trial runs." Eventually,
however, the team found that a Jupiter-like stable geometric arrangement
of storms would form if the storms were each surrounded by a ring of
winds that turned in the opposite direction from the spinning storms,
or a so-called anticyclonic ring. The presence of anticyclonic rings
causes the storms to repel each other, rather than merge.

Ingersoll says the research could help scientists better understand how
weather on Earth behaves.

"Other planets provide a much wider range of behaviors than what you
see on Earth," he says, "so you study the weather on other planets in
order to stress- test your theories."

========================================================================== Story Source: Materials provided by
California_Institute_of_Technology. Original written by Emily
Velasco. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Cheng Li, Andrew P. Ingersoll, Alexandra P. Klipfel, Harriet
Brettle.

Modeling the stability of polygonal patterns of vortices at the
poles of Jupiter as revealed by the Juno spacecraft. Proceedings
of the National Academy of Sciences, 2020; 202008440 DOI:
10.1073/pnas.2008440117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200924101940.htm

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