Anvil clouds tower more than 30 miles high. Amid the gathering gloom, 100 mph winds whip clouds across the sky. Painfully
brilliant lightning flashes punctuate the tumult. Meanwhile, clouds from another giant storm dump several inches of water,
every day, over an area more than 600 miles across.
Given the supernatural severity of these storms, and thunderheads three times higher than we see on our planet, we are
clearly not on the Earth. Welcome to the super-storms of Jupiter.
The giant planet of the Solar System is as different from the Earth as any planet could be. Jupiter is big enough to fit 1300
Earths inside, and it is made of gas and liquid throughout. Yet some of its storms are remarkably similar - though vaster in
scale - to thunderstorms on Earth. Even stranger, the latest results from NASA's Galileo spacecraft reveal that these storms
are powered in a completely different way from terrestrial thunderstorms.
There is a lot of activity we see on Jupiter that we see on Earth, says Peter J. Gierasch, professor of astronomy at
Cornell University. Along with colleagues from Cornell, the California Institute of Technology and NASA's Jet Propulsion
Laboratory, Gierasch has been studying views of Jupiter taken by Galileo on May 4, 1999. He continues: We see jet streams,
large cyclonic elements, large anti-cyclonic elements and many elements of unpredictability and turbulence.
They discovered that some of the storms here closely resemble clusters of thunderstorms found on Earth -
mesoscale convective
complexes. What is remarkable about the storm complexes on Jupiter, says Gierasch, is that they have the same physics as
thunderstorm clusters on Earth, but they are generated by a completely different type of heat source. Generally,
thunderstorms on Earth are small individual cells of cumulonimbus clouds, caused by summertime heat from the Sun. A mesoscale
convective complex is a cluster of many cells of thunderstorms, of the type that commonly strikes the midwestern United
States. These complexes are also formed by intense summertime heat.
The Sun's heat drives other weather patterns on Earth, of course, such as hurricanes and cyclones. The difference is the
source of the system's 'fuel'. Hurricanes and cyclones on Earth are fueled by the warm ocean. Mesoscale convective complexes
develop because of an instability in the atmosphere. Where it is warm near the Earth's surface in the summer and cooler
aloft, condensation rises and forms many cells of intense thunderclouds over a vast area. These summertime giants can last
for hours, even days, and dump unusually large amounts of rain.
On Jupiter, the colossal mesoscale convective complexes also last from 12 hours to several Earth days, producing
correspondingly huge deluges of rain over vast areas. The new results show that - contrary to previous belief - these
thunderstorm complexes are not fuelled by the Sun's heat, but instead develop from the intense heat emanating from Jupiter's
core.
The giant planet lies five times further from the Sun than the Earth, so it receives much less solar heat. On the other hand,
Jupiter's core is extremely hot. It still retains heat from the planet's original formation by collapse and compression of
the planet's huge gaseous bulk. It is in the process of cooling, and it will likely continue to cool for at least another
five billion years, Gierasch says.
Heat leaks upwards from a reservoir of highly compressed hydrogen in the planet's center, so this gaseous giant emits nearly
70 percent more heat than it absorbs from the Sun. The source of the stormy turbulence on Jupiter thus seems to be the planet
itself.
Mesoscale convective complexes on Earth are riven with lightning, seen dramatically from the space shuttle. What about
Jupiter's giant storm systems? Galileo's instruments are not able to detect lightning on the planet's sunlit side. But once
thinto the dark side, astronomers are able to see the lightning and confirm the existence of Jupiter's
mesoscale convective complexes .
These lightning bolts dwarf anything on Earth, according to Andrew. P. Ingersoll of the California Institute of Technology
and Blaine Little of ITRES Research, Calgary, Canada. They have measured the Jovian lightning strokes as several times the
size of the largest terrestrial bolts.
Jupiter's storms are not only spectacular. The new Galileo results suggest that the mesoscale convective complexes provide
the energy that drives the whole of Jupiter's powerful weather system. It's an almost-continuous cycle, Gierasch explains.
The storms develop and drop rain; the raindrops evaporate prior to reaching Jupiter's core heat-source, and rise again as
water vapour that convect upwards to start the next round of storms.
In the 400 years since the Italian astronomer Galileo first turned his telescope towards Jupiter, astronomers have puzzled
over its spectacular bands and whorls of swirling clouds. Now the giant planet's secret is out. Its turbulent clouds and
ferocious weather systems are fueled by its hidden superhot core, and driven by the greatest thunderstorms in the Solar
System.