Saul Trabal
EF4
Here's an email exchange I had with a Cassini scientist about Jupiter and Saturn's lightning. Very educational, and I'm sure you folks will find it interesting.
Enjoy.
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Dear Saul,
>1) Galileo was able to take photos of lightning on Jupiter's night
>side. Will Cassini be able to do the same thing at Saturn? If not, why
>not?
Cassini also took pictures of lightning on Jupiter's night side as we
passed by, and we learned something from doing that. I'm attaching a paper
we wrote on that. As for Saturn, in principle we can do the same thing,
and we will try when the apoapses of the Cassini orbits move from the
dayside to the nightside of Saturn next year. Whether we will be
successful is anyone's guess, for several reasons. First, we expect Saturn
to have less frequent lightning than Jupiter (even though we lucked out by
having an apparent thunderstorm with lightning present on our first orbit),
because it has less internal energy that it needs to release to space than
Jupiter does, so we may have to look longer before seeing
anything. Second, water clouds on Saturn may be deeper down than those on
Jupiter, and thunderstorms, even if present, may not always penetrate high
enough in Saturn's atmosphere to get above most of the high ammonia clouds
and haze where we can see them. We'll know for sure in 2006.
>2) Jupiter's lightning is 1,000 times stronger than Earth's, whereas
>Saturn's lightning is 1 million times stronger than Earth's. Why the
>difference in lightning strength on each gas giant?
Jupiter's lightning is stronger than Earth's because on Earth, the unstable
layer of the atmosphere over which air rises and accelerates in a
thunderstorm is only 10-15 kilometers deep. The deeper the layer and the
farther the air ries,the more it accelerates and the more lightning it
makes, all other things being equal. On Jupiter, the unstable layer is
about 50 kilometers deep, so rising air may accelerate to faster speeds and
make stronger lightning. ON Saturn, we only have this one example of
electrostatic discharges so far, and that may have been an unusually strong
storm, so it's too early to conclude that Saturn's lightning is stronger
than Jupiter's. It could turn out that most of Saturn's storms don't get
high enough for us to detect them, so all we will see are the biggest ones,
so that could be a biased view of how strong Saturn lightning is on average.
>I wish you and your comrades the best of luck with Hyugens.
We're crossing our fingers that all goes well tomorrow morning!
Regards,
Tony Del Genio
Anthony D. Del Genio
NASA Goddard Institute for Space Studies
Enjoy.
----------------------------------------------------------
Dear Saul,
>1) Galileo was able to take photos of lightning on Jupiter's night
>side. Will Cassini be able to do the same thing at Saturn? If not, why
>not?
Cassini also took pictures of lightning on Jupiter's night side as we
passed by, and we learned something from doing that. I'm attaching a paper
we wrote on that. As for Saturn, in principle we can do the same thing,
and we will try when the apoapses of the Cassini orbits move from the
dayside to the nightside of Saturn next year. Whether we will be
successful is anyone's guess, for several reasons. First, we expect Saturn
to have less frequent lightning than Jupiter (even though we lucked out by
having an apparent thunderstorm with lightning present on our first orbit),
because it has less internal energy that it needs to release to space than
Jupiter does, so we may have to look longer before seeing
anything. Second, water clouds on Saturn may be deeper down than those on
Jupiter, and thunderstorms, even if present, may not always penetrate high
enough in Saturn's atmosphere to get above most of the high ammonia clouds
and haze where we can see them. We'll know for sure in 2006.
>2) Jupiter's lightning is 1,000 times stronger than Earth's, whereas
>Saturn's lightning is 1 million times stronger than Earth's. Why the
>difference in lightning strength on each gas giant?
Jupiter's lightning is stronger than Earth's because on Earth, the unstable
layer of the atmosphere over which air rises and accelerates in a
thunderstorm is only 10-15 kilometers deep. The deeper the layer and the
farther the air ries,the more it accelerates and the more lightning it
makes, all other things being equal. On Jupiter, the unstable layer is
about 50 kilometers deep, so rising air may accelerate to faster speeds and
make stronger lightning. ON Saturn, we only have this one example of
electrostatic discharges so far, and that may have been an unusually strong
storm, so it's too early to conclude that Saturn's lightning is stronger
than Jupiter's. It could turn out that most of Saturn's storms don't get
high enough for us to detect them, so all we will see are the biggest ones,
so that could be a biased view of how strong Saturn lightning is on average.
>I wish you and your comrades the best of luck with Hyugens.
We're crossing our fingers that all goes well tomorrow morning!
Regards,
Tony Del Genio
Anthony D. Del Genio
NASA Goddard Institute for Space Studies
