**FTS-NASA**

**March 29, 2005**

**1:00 p.m. CST**

Coordinator Excuse me. I'd like to remind all parties this call is being
recorded. If anyone has any objections, you may disconnect at this time.
Thank you. You may begin.

T. Ray Thank you, everyone and welcome to our CHARM telecon for the
month. This month we have a terrific speaker, Dr. Andy Ingersoll, who's
one of the Imaging team members. He specializes in atmospheres of giant
planets. He's going to be talking to us today about the mighty winds of
Saturn. There are some movies to download in addition to the PowerPoint
presentation. If you download the movies now they'll be all ready to go
on your own computers when we get to that point in the presentation. If
everybody tries to download right at that moment, then we end up having
trouble. So you might want to go ahead and download those movies ahead
of time. We have the line for the full two hours, but usually with one
speaker we'll go somewhere around one hour. We will take all the
questions that we have. Andy, I'll turn it over to you.

Dr. Ingersoll Hey, terrific. I'd be very happy to have interruptions and
questions. If they get out of hand, I'll just tell you to shut up, but I
would welcome them. So feel free to interrupt at any time. The movies
are a little tricky on my computer. So I might defer the movies until
the end, because I've got some still sequences that pretty much show the
same thing, but maybe not as graphically. Let me tell you about myself.
I was trained as a meteorologist but somewhere along the line realized
that I didn't want to forecast every day and I would much rather study
other planets, where we knew much less about their atmospheres. Somehow
the problems seemed more challenging. We were struggling with more basic
issues than the weather forecasters were, but of course I'm sure there
are some weather forecasters on the line here who might take issue with
that. Perhaps it's just a temperamental thing that suits me.

So, you can see the first slide, it's got a little number one in the
bottom right. It's sort of an outline of what I want to talk about:
winds and temperatures, a very fundamental subject to every atmospheric
scientist. The strange thing is that Saturn, even though it receives one
percent of the amount of sunlight that the Earth does, has winds that
are ten times stronger than the Earth's winds. For a while, and that's
part of the subject, it was the windiest planet in the solar system.

The way we measure winds on Earth is relative to the solid parts of the
planet. That gets a little tricky when you have a gaseous planet, so
determining the reference range from which to measure the motions of the
clouds gets a little tricky. That's the second subject I want to talk
about. What we have to do is use the magnetic field of the planet and
the radio emissions that are tied to the magnetic field. It's sort of an
indirect way of deciding how fast the inside of the planet is rotating.
Then the storms in the giant planets are very interesting because they
last for so long. Saturn doesn't have anything quite like Jupiter's
great red spot, which has been around since the telescope was invented,
but it's got some long-lived storms. Some of them we even have evidence
of lightning going on in those storms. Probably that, itself, is
evidence of falling ice particles and even raindrops somewhere down
inside the clouds. Then I'll close with work in progress on all the
interesting chemistry when you have a hydrogen helium atmosphere and
just about everything in the periodic table, carbon, nitrogen,
phosphorus. Probably even oxygen down deep, but it's locked up with
hydrogen, so I'll talk a little bit about that.

Please switch to the second slide, and that's actually sort of
Meteorology 101, this is descriptions of the Earth. The upper left is
the radiation budget. One curve there is labeled "Absorbed Solar." That
is the watts, that's power per square meter, absorbed by the Earth. This
is averaged over the year. It's greater at the equator because the sun
is shining down at normal incidence at the equator and it's oblique at
the poles. Then there's the emitted long-wave radiation that's in the
infrared, and that is a more gently humped function. That depends on the
temperature at each latitude. It's colder at the poles, so there's less
emission in the emitted long-wave band. The area under the two curves is
the same, because the Earth isn't gaining or losing that energy, but at
each latitude the two curves don't balance out. What's going on is the
atmosphere and the oceans are transporting heat out of the equator to
make up for the extra sunlight that's being deposited there. They're
moving it to the poles, where there's extra cooling going on and there's
long-wave radiation. That's the way the Earth keeps itself in balance.

> The slide on the lower left shows that that transport from the equator
> to the poles is about equally taken up by the atmosphere and the
> oceans. This is kind of interesting when you start thinking about the
> giant planets, because the giant planets are completely gaseous, right
> down to the core. In a sense they're like an atmosphere with an ocean
> underneath so you wonder how does this pole ward heat transport take
> place on a giant planet? Furthermore, at least some of these things we
> can measure. For instance, we can measure the absorbed sunlight on the
> giant planet from spacecraft and we can measure the emitted long wave.
> What we find, and I'll show you in a second, is that at least on
> Saturn and most of the giant planets, the temperatures are pretty much
> the same at the equator as they are at the poles. It's not like the
> Earth, where there's a 30 degree Celsius difference between equator
> and poles. The giant planets' temperatures are just about the same at
> the equator and the pole and the emitted long wave is pretty much a
> flat curve, the same at the equator as it is at the poles. The
> thinking is that the ocean of these giant planets, which is nothing
> more than the atmosphere that goes on below the clouds, is much more
> active than it is on the Earth. It transports the heat very
> effectively and effectively wipes out all of the temperature gradients
> between equator and pole. So we're going to talk a bit about that.
>
> On the right of this slide are the zonal winds, zonal meaning to the
> east. Just focus on the upper right, those are the winds. Those sort
> of bullseyes in each hemisphere are the winds in meters per second.
> Those two centers of the bullseyes are the jet streams that we use to
> fly from west to east, get a little boost. 40 meters per second is
> about 90 miles per hour, so those are the jet streams on Earth. Let me
> now show you the jet streams on the giant planets. So let's go to
> slide number three.
>
> Look at the lower right, there's Saturn at the time of Voyager in the
> early '80s. You can see that at the equator of Saturn the wind speed
> is 450 meters per second, which is ten times the speed of the Earth's
> jet stream. Jupiter looks kind of puny next to Saturn there---it's got
> jet streams that get up to 150 meters per second. Uranus and Neptune,
> just as windy, almost as windy as Saturn, not quite. That's a mystery,
> because there's just so little energy in the outer solar system, why
> should the winds be so much stronger than they are here at home? Well,
> since it is a mystery I'm not going to answer that for you, although
> we've got theories.
>
> One theory is that dissipation of energy, the turbulence in these
> atmospheres, is less, much less, than it is on Earth. The turbulence
> is somehow connected to sunlight, and since there's so much less
> sunlight there's that much less turbulence. Without the turbulence the
> winds can just build up and coast along with nothing to slow them
> down. That's why, at least according to this speculative theory, the
> winds don't decrease as you go out in the solar system.
>
> How do we actually measure the winds? Well, let's go to slide number
> four. This is just a small portion of Saturn's atmosphere in a picture
> taken by the imaging system, which is basically a camera like your
> handheld ECD camera, not video camera but your movie camera. We take
> sequences. The planet rotates at approximately a ten hour period, so
> you can see the same real estate, so to speak, every ten hours. You
> take a picture every ten hours, and you can see the clouds move over
> that ten hour period. Then it becomes a simple---well, it's sometimes
> a fairly complicated---programming challenge to teach a program to
> recognize the same cloud ten hours later, because that cloud may have
> changed. It's actually somewhat easier to teach a junior high school
> student to recognize the same cloud. It's a little harder to get a
> computer program to do it automatically. Nevertheless, it's these
> little curly-Q's and wisps that we track from one ten hour period to
> the next. That's how we measure the wind.
>
> Next slide, this is the one labeled "ISS Tracking Spots in Sequence of
> Images." Sometimes we track these little amorphous wisps, and
> sometimes we track these well-defined spots. Now, you have to remember
> we're looking at an object that's ten times bigger than the Earth and
> so these spots are not small, really. They're the size of a
> terrestrial hurricane, these dark spots and light spots. In fact, they
> probably are somewhat analogous to terrestrial hurricanes. Some of
> them are emitting radio signals that look very much like the radio
> signals emitted by a thunderstorm when there's lightning,
> electrostatic discharges going on. I'll tell you more about that. Now,
> so far I've been showing you the images taken by the camera, which
> operates in the visible and just beyond the visible range, both sides,
> ultraviolet and near infrared.
>
> But, let me show you some pictures that were taken way out in the
> infrared, where we're looking at the heat, the thermal emission of the
> planet. That's slide number six. This actually was not taken by
> Cassini. This was taken by Glenn Orton at one of the telescopes at
> Hawaii, the IRTF telescope. I show this slide just to show you the
> different options we have when we peer at the atmosphere of a planet
> and the different interpretations of what you see.
>
> When you look at an ordinary picture, like the ones I showed before,
> you're basically looking at cloud particles, some of which are bright
> colored and some are dark colored. The contrast is just tied in with
> the composition of the cloud particles. Here, the contrast is tied in
> with the holes in the clouds. When there's a hole in the cloud you see
> into deeper levels where it is warmer and so bright in this image.
> Especially in the right hand image, but actually both of them, bright
> is something that's a hole in the clouds. You're seeing the deeper,
> warmer levels. So what you see there is that right at the pole there
> is this hole in the clouds surrounded by another ring shaped hole,
> whereas up near the equator there's a number of bands that are quite
> cold, indicating those are high clouds sticking up high up in the
> atmosphere where it's quite cold. The same kind of technique is used
> in daily weather images of the Earth. They show you visible images but
> they also show you infrared images. The high clouds show up as cold
> things, and the holes in the clouds at the surface of the Earth show
> up warm, for the same reason as we're seeing here.
>
> So, let's go on to one of the hot topics when Cassini got to Saturn.
> This concerns whether Saturn is still the windiest planet in the solar
> system, or whether it's somehow slowed down and lost its standing. So,
> the next slide, which doesn't have a number but it's a graph has a
> bunch of colored points on it. What's plotted here is latitude running
> up and down the figure. The equator is not labeled, but you can see
> it's in between plus ten and minus ten. We couldn't see the northern
> hemisphere very well because the rings were in the way. The ring
> shadow was blocking the sun, so the northern hemisphere wasn't
> illuminated at the time these data were taken, when Cassini arrived.
> Then along the lower part of the graph you can see it's labeled in
> velocity and meters per second. I'll just remind you again that 400
> meters per second is 900 miles an hour. The solid curve, the black
> curve, is the Voyager data. You can see the 450 meters per second wind
> at the equator. The yellow dots were taken by the Hubble Space
> Telescope. Sanchez La Vega is the scientist who led the team that made
> those observations. You can see that the yellow dots agree with the
> solid line in the southern hemisphere, until you get up to about 15
> degrees south latitude. Then closer to the equator the yellow dots
> indicate a much slower wind speed, just a little less than 300 meters
> per second, which is an enormous change in the wind.
>
> The Hubble data were taken in the late '90s, over a several year
> period. So when Cassini got to Saturn we were all wondering have the
> winds permanently slowed down or have they sped up again? What had
> happened? So we started measuring winds. We're able to look at a
> number of different wavelengths (this is the camera again), and the
> different wavelengths allow us to look at different altitudes. In the
> red and green filters we're just looking at wavelengths where we can
> see down to the main cloud deck. Different people did the analysis and
> you can see that the red and green, at least in the equatorial zone,
> fell somewhere in between the Voyager data and the Hubble data from
> the mid and late '90s. So, yes, the winds seemed to have slowed down
> from the Voyager days, but no, not as much as they had slowed in the
> 1990s. But that's not the whole story, because we have the methane
> filter, which allows us to look at very thin clouds that are almost
> transparent in the continuum filters, like red and green, but show up
> in the methane filter. These thin clouds are higher up, sort of like a
> Cirrus cloud filter. There, you can see that the blue dots agree with
> the Hubble data. The green and red and blue dots are all from the same
> time, so what we're seeing is the wind seems to be decreasing with
> altitude. We're not getting the same speed when we look at the methane
> filter as when we look at the continuum filters.
>
> Just to put this in perspective, when you're out at a very cold
> planet, the energy that the planet radiates is not very great. It's
> roughly one or two percent of what the Earth radiates on a per area
> basis. Yet the winds have a huge kinetic energy. If you took that 450
> meters per second wind, slowed it down to below 300 meters, and
> converted all that kinetic energy into heat, it would take several
> years for the planet to radiate away that much heat and the equator
> would have heated up in the meantime. We don't see much evidence of
> that. So, we're still arguing about whether the winds actually slowed
> down or whether the different groups have just been looking at winds
> at different altitudes.
>
> That brings up the next slide, which is labeled slide number eight.
> This is another instrument of Cassini, CIRS. It's an infrared
> spectrometer, and it can measure temperatures in the atmosphere. The
> upper panel shows just that, temperatures in the atmosphere. You can
> see again the southern hemisphere; latitude goes from zero out to
> minus 90 in the southern hemisphere. The vertical is altitude in
> pressure units, millibars. (The Earth's sea level pressure is about
> 1000 millibars.) You can see the lines are very flat and horizontal
> near the bottom. In fact, they're pretty flat everywhere. That's one
> of the things I alluded to earlier, that really the temperatures at
> the poles on the giant planets, including Saturn, are pretty much the
> same as the temperatures at the equator. There's no 30 degree
> temperature difference as there is on Earth. That's probably, as I
> said, because the atmosphere is so efficient in transporting heat pole
> ward. However, you can see closer to the equator, right over on the
> left side of that upper curve, the lines aren't quite flat. They bulge
> upwards or bulge downwards. That represents a temperature contrast
> between the equator and the latitudes like around ten, fifteen degrees
> south latitude.
>
> From the temperature differences you can compute pressure differences.
> With a little understanding of Coriolus forces, you can turn that into
> winds. The winds are plotted at the lower scale, the lower graph.
> These winds are not measured the way the camera measures them, by
> tracking clouds. They're inferred from something called the thermal
> wind equation. So it's a somewhat indirect way to compute winds, but
> you can see that the winds fall off with altitude from maybe 400
> meters per second in the lower left, down to 200 meters per second by
> the time you get up to one millibar. That is consistent with, or at
> least qualitatively consistent with, the graph I showed earlier, which
> is the higher you look, the slower the wind.
>
> So as I said, we're still arguing about whether the winds have
> actually slowed down. Maybe we're just looking at the clouds having
> risen, and we're seeing winds at higher altitude now than we were,
> say, during the Voyager era. Perhaps we were seeing winds at lower
> altitude where they're moving more rapidly.
>
> There's another instrument, let's move on here, on the Cassini
> spacecraft called VIMS, which is Visible Infrared Mapping
> Spectrometer. It has a different handle on the altitude that you're
> looking at. It can see, in certain wavelengths, the thermal emission.
> The upper left panel shows five microns for reference. That's about
> ten times the wavelength of visible light. This is thermal emission;
> the little bright places are holes in the clouds. I'm not going to
> talk about the other wavelengths that they look at, but the next slide
> shows how VIMS has tracked the holes in the clouds. So the little
> arrows point to little bright spots. They are seeing quite deep at
> this particular wavelength. The gases in the atmosphere are very
> transparent at this wavelength. So they're seeing holes in, not just
> any old cloud, but in a deep cloud. They've tracked these little
> bright spots. You can see it's a difficult observational task because
> their resolution is not all that great. But they can measure the
> winds. From the spectroscopy and knowledge of their instrument, they
> know that they're looking deep into the atmosphere. The next slide
> gives the basic results, the second bullet there. They're measuring
> high speeds. They're measuring speeds like 465 meters per second right
> at the equator, or two degrees north of the equator, which is
> consistent with the Voyager data from the early '80s, but not with the
> Hubble observations in the 1990s. The last bullet says that they're
> more sensitive to the deep clouds---cloud base---and not the cloud
> top.
>
> That's where we stand right now on winds and whether Saturn is still
> the windiest planet or not. My own feeling is it probably still is and
> what's happened is that the clouds that we see in the various
> wavelengths have moved up and down over the past few decades.
> Sometimes we're sampling high altitudes and sometimes low altitudes.

M A question.

Dr. Ingersoll Yes?

M The variation of the winds over the years, and I don't remember how
many years it is between Voyager and Cassini now, maybe 30 years or
something?

Dr. Ingersoll Yes.

M Would that possibly have something to do with the tilt of the rings
and maybe the shadow that's on the planet?

Dr. Ingersoll It certainly could. As I say, we haven't settled it yet,
and there are several possibilities. I've kind of focused in on the
possibility that nothing has changed except for the height of the clouds
where we're measuring the winds and the winds themselves have not
changed. But there's another possibility, which is the one you
mentioned, that seasonal changes on Saturn have actually caused a
genuine change in the heating of the atmosphere. Especially because of
the way the ring shadow switches back and forth from one hemisphere to
the other, and actually disappears when the rings are edge on to the
sun, this may have actually caused a genuine change in the wind speeds
at any given altitude. My own feeling is that because there's so much
kinetic energy that has to be shifted back and forth and you don't
really have a lot of power in that atmosphere because it's so cold, that
it's unlikely. But you could find other scientists who would disagree
with me. How's that for an answer?

M That's good. Thanks a lot.

Dr. Ingersoll Now, let's change gears a little bit. Everything I've said
so far about the wind assumes a certain reference frame. As you think
about the Earth's atmosphere, we don't measure our winds relative to an
inertial reference frame; we measure it relative to a rotating reference
frame, which is the solid planet. If you ignore that or if you were to
add in the speed due to the rotation of the Earth, we'd all be going
eastward at an enormous rate, supersonic speeds, in fact. Yet we have
eastward and westward winds relative to the solid planet.

> So, the question is, how are we going to choose the reference frame
> for a gaseous planet? In the case of Saturn, we didn't have a
> reference frame until Voyager got there. Voyager detected radio waves
> with kilometer wavelengths, very long radio waves. Kilometric
> radiation, it's called. It came and went very regularly, with a very
> definite period, approximately ten hours and 40 minute periods. So the
> people in charge of that instrument took an average of all the
> kilometric radio waves and defined a period, and said okay, our best
> estimate of the Saturn radio period is ten hours and 39.4 minutes.
> Everyone said, okay, even though there's some uncertainty in that
> measurement, let's define that as the reference frame that we're going
> to measure winds and everything else relative to. So that became the
> period of Saturn that everyone used in their computation. The idea is
> that the radio source is somehow tied to the magnetic field, which is
> in this diagram here, figure number 12. The magnetic field is being
> generated inside Saturn, deep down. The idea goes it has some kind of
> a wobble to it; it's not just straight up and down axisymmetric. So
> that wobble translates into a periodic radio source. By measuring the
> radio, we're really measuring the rotation of Saturn's interior,
> that's the idea. Cassini kind of upset that idea and caused a lot of
> trouble, although there were hints from Earth based observations of
> Saturn that the idea was in trouble.
>
> The next slide, slide number 13, shows the Voyager period, 10 hours 39
> minutes and 24 seconds, plus or minus 7 seconds. But now it appears
> that that period of the kilometric radiation has changed. When Cassini
> went by it was 10 hours, 45 minutes and 45 seconds. There's no way
> that the interior of the planet could have changed its rotation rate,
> there's just too much angular momentum to be gotten rid of. What it
> really means is that the kilometric radiation is not a good handle on
> the rotation of Saturn, it's not as good as we thought it was. That
> really throws everything up in the air, everything to do with the wind
> up in the air. The current status is that although we can see things
> coming around on successive rotations and we can see at certain
> latitudes they come around with slightly different periods, we don't
> know what reference period to use anymore. We're struck right there,
> right now. Now, the way out of that, if the radio signals are not
> attached to the magnetic field, maybe we can use the magnetic field
> itself, if it has some kind of asymmetry. We can use it to determine
> the rotation of the interior directly.
>
> Well, slide number 14 shows the magnetic field data from the Saturn
> orbit insertion back last summer. These are three components of the
> magnetic field and the total magnetic field. These are extremely
> boring curves, so boring that it's discouraging. What it says is that
> the magnetic field, unlike Earth's and Jupiter's fields (which are
> tilted by about ten degrees or eleven degrees with respect to the
> rotation axis and therefore have a very definite wobble like a
> wobbling top) Saturn's magnetic field is straight up and down. It's
> like a top that is spinning perfectly up and down and doesn't wobble
> at all. Therefore, so far we haven't been able to use the magnetic
> field as a way of determining rotation, because it doesn't wobble. So,
> we're kind of waiting for more orbits and more close passes to the
> planet in the hope that we'll find some wobbling in the magnetic field
> that will nail down the rotation of Saturn's interior at long last.
> Right now it's too symmetric to tell.
>
> Let's go on. Let's move to nice colorful pictures on slide 15. This is
> a false color picture. False color means that we took an image through
> filters that the eye can't actually use, ultraviolet and infrared
> beyond the visible red, but these filters tell us a different story
> than what our eyes would see. For instance, with certain combinations
> of these filters, we can detect the height of the clouds rather than
> the colors of the clouds. Is there someone there? No. That very sort
> of ornate white cloud in the middle upper part, which we nicknamed the
> Dragon Storm, for obvious reasons, is a high cloud. In fact, there are
> certain latitudes where the storms are found. The blue dot at the same
> latitude and the Dragon Storm are all in a particular shear zone.
>
> Let me show you slide 16, which you've already seen. Look down at
> latitude between about 35 and 40. At latitude 35, that's a minimum in
> the velocity. Or you can say it another way, the winds are to the west
> right there. Most of Saturn's winds are to the east, but right at 35
> degrees the winds are weakly westward. Then as you move further south,
> at say 40 degrees south, the winds are eastward at about 125 meters
> per second. So, in that band between 35 south and 40 south is what we
> call, "Spot Alley," because that's where most of the storms that we
> saw, and in the movies most of the action was in spot alley. If you
> put a pinwheel or some kind of floating device at that latitude in
> between those two jet streams, the pinwheel would rotate in a
> counterclockwise direction. So we say this is anti-cyclonic, this is
> in the southern hemisphere, sort of like a high pressure center in the
> southern hemisphere on Earth, except it's a high pressure band. That's
> where all the spots are on Saturn.
>
> The next slide shows a time sequence, and the movies show this same
> time sequence. The way you look at it is, this is number 17, there's
> eight panels. Look across the top row and then shift your gaze and
> look across the bottom row. What you see is two little dark spots
> coming together, spinning around each other in a counterclockwise
> direction, and then merging with each other. The pictures were taken
> at different times and the spots are not always at the same place
> relative to the spacecraft. So, for instance, on the lower panel, the
> second from the left, these spots are way over near the right side and
> then the third from the left they're over on the left, that's not
> important, that's just the peculiarities of when the picture was
> taken. What you should see there is that a merger took place between
> these two guys. Some of these spots are months old. They're basically
> little hurricanes that lasted for months and then merged. If they
> merged, then of course you have fewer hurricanes, one fewer hurricane
> if two of them merged. You have to ask, well, where do they come from?
>
> The next slide is the Dragon Storm. This one is another time sequence.
> You have to look down the page on the left column, then down the page
> on the center column, then down the page on the right column. In the
> last column, in fact near the bottom three panels, if you study it a
> little bit you can see some dark spots forming. It's not entirely
> clear, even to us who have studied this sequence at great length, but
> we're pretty sure that we're seeing spots forming here. So our
> interpretation of the Dragon Storm is that it's a particularly active
> site of vigorous convection, upwelling of material from below, clouds
> forming high up in the atmosphere. We can tell it's high because of
> the way it appears in the different filters. It's also spawning little
> stable hurricanes that go spinning off east or westward. One other
> thing about the Dragon Storm (a very interesting thing about it) is
> that it seems to be a source of these radio emissions that look very
> much like the radio emissions from lightning strokes on Earth.
>
> The next slide, number 19, is kind of complicated, but I think I can
> explain it quickly. This is a ten or twelve day period. Each one of
> the little solid spiky curves is telling you how many of these radio
> electrostatic discharges were detected per hour. You can see that on
> some days, one day in particular around day 257, it was just flashing
> away---60 per hour of these short burst radio electrostatic
> discharges. Let's call them SEDs, Saturn Electrostatic Discharge,
> these pulses. Sixty pulses per hour is like 60 lightning bolts per
> hour. These were detected by the RPWS instrument on the Cassini
> spacecraft. You can see also that the storms are detected--- the SEDs
> are detected---every ten hours, approximately every ten hours. There's
> a spike that lasts for a couple hours. There are sometimes when
> there's no spike, like a little bit after day 252. There was nothing
> between day 258 and 259, there was a couple of days SEDs were missing.
> But mostly every Saturn day, which was ten hours and 40 minutes, there
> were electrostatic discharges.
>
> The little inset up in the upper left shows all of these over-plotted
> on top of each other, and then there's this little asterisk there. So
> the spikes, these curves that go up and then go down, those are the
> electrostatic discharges detected by the radio instruments. The
> asterisks are the Dragon Storm as observed by the camera. We plotted
> the asterisk at the time that the Dragon Storm was crossing the
> central line of the disk, as seen by the Cassini spacecraft. You can
> see that there's a connection, in the sense that every time the Dragon
> Storm was crossing the center of the disk, the SEDs were sort of dying
> down. The maximum SED rate preceded the Dragon Storm crossing the
> center of the disk by about a few tenths of a Saturn day, which means
> a few hours. So, just imagine yourself on the Cassini spacecraft
> watching the Dragon Storm. It comes up over the edge of the planet in
> the morning on the morning side, on the left side. Then as Saturn
> rotates the Dragon Storm crosses over and then sets on the right side.
> When the Dragon Storm is just coming up over the edge of the planet on
> the left, is when the SEDs start up. They go on for a few hours. Then
> when the Dragon Storm is near the center of the disk, the SEDs kind of
> die away.
>
> So, it's a little strange that the SEDs did not peak along with the
> central crossing of the Dragon Storms. On the other hand, the two are
> definitely synchronized. This is just a twelve day period and the
> relation between the two was a constant during the twelve day period.
> We actually have about twice that long, and they were synchronized for
> the whole period. So, current thinking is that the ionosphere of
> Saturn, or at least one theory, is that the ionosphere of Saturn turns
> on during the day. (Oh, I have to tell you one more thing---during
> this period Saturn was half illuminated. The day side of Saturn was on
> the right side of the image, and the night side of Saturn was on the
> left side, sort of like a half illuminated moon. So when the Dragon
> Storm was crossing the center of the disk, its local time was about
> 6:00 a.m., and it was actually moving from darkness into light.) One
> thing we know about ionospheres is that they sort of turn on when the
> sun hits them. You get a lot more charging of the upper atmosphere
> when the sun hits it. The charge in the upper atmosphere can block the
> radio waves from coming out and getting out into space. So one theory
> is that the electrostatic discharges were actually continuing as the
> Dragon Storm crossed the central part of the disk and moved over to
> the right side, but that we couldn't hear them from Cassini because
> the ionosphere was blocking the radio waves.

M A question there.

Dr. Ingersoll Yes?

M On this graph you have universal time, now is that in relation to
Saturn or is that ...?

Dr. Ingersoll No, that's Greenwich time. That's probably Greenwich time
at Saturn. We subtract off the light travel time between Saturn and the
spacecraft or Saturn and the Earth.

M Thanks.

Dr. Ingersoll So, this is another work in progress, I seem to be full of
them. We don't fully understand why the SEDs didn't peak up just as the
Dragon Storm was in the center of the disk, but one theory has to do
with the ionosphere blocking the radio waves during the daytime.

> So I'm going to leave that subject and really go on to my last
> subject, which is even more just kind of a status report of different
> instruments just to show you the power of what the different
> instruments can do, even though some of the data haven't been fully
> analyzed and some of the big questions haven't been answered.

Slide number 20 shows the ultraviolet spectrometer, and it gets the
ultraviolet spectrum in that long white slit, which, in this particular
image, runs from pole to pole on the planet. The green dots inside that
slit show you the intensity of the hydrogen band emission, and you can
see the two auroras. Saturn has an aurora, aurora borealis, produced by
the same kind of mechanism: Electrically charged particles that are not
resting on top of the atmosphere but are actually flying about trapped
in the magnetic field and moving at high speeds, crash down on the top
of the atmosphere and cause it to glow. That's what causes the auroras
on Earth, Jupiter, Saturn. The differences between the different auroras
on the different planets have to do with the nature of the charged
particles that are coming down, where they originate, and secondly, the
atmosphere that they're crashing into.

> On Jupiter, the charged particles in the magnetosphere, which is this
> region around the planet, actually come from sulfur, sulfur dioxide,
> that's emitted by the volcanoes of Io, Io being one of the moons of
> Jupiter. So, what you have is charged sulfur and oxygen in the
> magnetosphere and electrons. That mixture of stuff occasionally
> crashes into the planet and causes Jovian auroras. On Saturn, there's
> no volcanic moon so there's no sulfur dioxide that we know of, but
> there's lots of ice. The rings are, if not made of ice, certainly
> coated with ice. We can see the spectrum of ice when we look at light
> reflected off the rings, and the moons like Enceladus have icy
> surfaces. Particles crashing into that ice will knock loose hydrogen
> and oxygen. So a lot of the charged particles coming into the Saturn
> atmosphere are hydrogen and oxygen. In addition, what they're hitting
> is a hydrogen atmosphere. So you see the glow of, in this case, the
> hydrogen emission.
>
> Let's move on. You can look at the ultraviolet light, spread it out in
> its spectrum, compare that spectrum with lab spectra and you can see
> the agreement. The amplitude is maybe less important, because it
> depends on the rate at which you bombard things. The wavelength is
> mostly telling you the composition of the particles involved. You can
> see that there's a very close resemblance in the wavelength at which
> the spikes occur. That says that the materials in the lab pretty much
> match the materials on Saturn, even if the rate at which you're
> bombarding things don't quite match.
>
> There's really hydrogen all over the place. If you go to slide 22 you
> can see the hydrogen aurora. Some of it is just atomic hydrogen H and
> some of it's molecular hydrogen H2, but it's all over the place. In
> fact, they're trying to sort out what fraction of the hydrogen comes
> from the solar wind and what fraction comes from the ice in the
> atmosphere of Saturn. Of course, if you have solar wind then you also
> have helium, and that's one of the ways of distinguishing where things
> are coming from.
>
> Let's move on to slide 23, which again shows ultraviolet spectra. The
> solid line is the measured ultraviolet spectrum from Saturn and the
> dashed line is a laboratory spectrum of acetylene, which is C2H2, two
> carbons, two hydrogens. You can see that where acetylene is an
> absorber, where the dash line is low---let me see here, what are we
> getting---try and understand the anti-correlation between these two
> curves. It's quite clear that where acetylene---okay, I'm beyond my
> depth here---you can certainly see that this is acetylene, because
> every spike corresponds to a dip in the other curve, but exactly
> what's going on, I guess I don't quite know. Let's just take this
> slide as an illustration of how clear the signature is of each gas.
> When you take a spectrum, each gas leaves a very clear signature and
> you can certainly see the signature of acetylene in this slide.
>
> Incidentally, acetylene is sort of interesting. In a hydrogen rich
> atmosphere at chemical equilibrium, if you toss in a little carbon,
> that carbon will form methane, which is CH4. You won't get very much
> acetylene at all. So the fact that you do have some C2H2 in addition
> to the CH4, says that there's some interesting chemistry going on in
> the atmosphere, probably driven by the charged particles and the
> ultraviolet light that's coming in from the sun.
>
> Moving on here, we're getting close to the end. This is a different
> wavelength altogether, now out in the thermal infrared. This is
> thermal emission just around ten microns, twenty times the wavelength
> of visible light. Here you see the signature of different gases. CH4,
> which is methane. CH3D where D stands for deuterium, which is a heavy
> isotope of hydrogen. It's chemically the same as hydrogen, but it's
> got a proton and a neutron in the nucleus instead of just a single
> proton. The CH3D is there in much lower abundance than the CH4, but
> yet you can detect it. Then phosphorus, in combination with hydrogen,
> is present.
>
> Different portions of the spectrum show the signatures of different
> gases.
>
> Here's another one. It doesn't have a number, but it would be slide
> number 25. Even farther out in the infrared you can see CH4, which is
> methane; NH3, which is ammonia; and phosphine, the PH3.
>
> I guess there are several questions that the spectroscopy is
> addressing, fundamental questions. One is: What are the giant planets
> made of, really? We know that they're mostly hydrogen and helium, and
> they have trace amounts of just about every other element in the
> periodic table. In that sense, they resemble the composition of the
> sun. The sun's composition is presumably the composition of the
> original stuff out of which the planets formed, but the ratio of
> things like carbon to hydrogen, or nitrogen to hydrogen, or phosphorus
> to hydrogen, or so on, those ratios are not quite the same as those
> ratios on the sun. In fact, on Jupiter these things like carbon,
> nitrogen, sulfur, are enriched by approximately a factor of three
> compared to their abundance on the sun. By that I mean, let's take
> carbon: the C to H ratio on Jupiter is a very small number, it's like
> ten to the minus three or ten to the minus four, but that very small
> number is nonetheless three times larger than the C to H ratio on the
> sun, which we can get from spectroscopy also. That tells us something
> about how Jupiter formed and how it got its heavier elements, like
> carbon, nitrogen and so on. So we're very much interested in doing the
> same thing for Saturn, because there's already good evidence that
> Saturn is different from Jupiter. It has an even higher enrichment in
> the heavier elements relative to Jupiter and relative to the sun.
>
> That's all work in progress and I can't really tell you how it's going
> to go. I'll just move to my last slide, which is, "That's All for Now,
> Expect Monthly Updates." Really, that's the end of my presentation. I
> can take questions, we can talk and we can look at movies.

H. Nauert Hello. I have a question. This is Hank Nauert in Lenexa,
Kansas, Solar System Ambassador. On slide 18 where you show the
spots---Is this an infrared image?

Dr. Ingersoll No, it's the camera, which means that it's visible light
or slightly beyond visible. I guess it could be called near infrared.
It's just beyond the red, probably around .7 microns. It's not thermal
emission like I showed you--- ten microns or things like that.

H. Nauert Does the dark spot indicate deeper, toward the center of the
planet?

Dr. Ingersoll Yes. But it's not a big difference; it's maybe a ten
kilometer difference.

H. Nauert I see.

Dr. Ingersoll But yes, the white stuff you can think of as a towering
cumulous ten kilometers above the rest of the cloud deck.

H. Nauert Each of the dark spots seem to be encircled by a lighter spot,
is that similar to the indications of a hurricane or a thunderstorm here
on Earth?

Dr. Ingersoll You're sort of thinking maybe this is the eye of a
hurricane. Possibly so. I guess I don't really know. Someone may know,
but I don't think any of us know, the exact details of these things. For
one thing, we have to get closer to them to really probe into their
detailed structures. Right now they look like dots.

H. Nauert What kind of distances were these images taken?

Dr. Ingersoll The pixel size, which is the smallest block of the grid
our camera projected onto the planet, for some of these images is 100
kilometers. The very best one is 100 kilometers. We can do much better
later on.

H. Nauert What kind of distance would the camera be from ...?

Dr. Ingersoll Let's be more specific. When the camera is a million
kilometers from Saturn the pixel size is six kilometers. Most of our
images that we have here, the spacecraft was more like tens of millions
of kilometers. So when the camera is a million kilometers---we have a
powerful telescope on the spacecraft obviously---we can resolve a six
kilometer pixel. But we weren't that lucky on the initial images. We had
to share the time with other instruments, basically, and other targets
we were looking at.

H. Nauert I sure do appreciate the information that you've given us
today.

Dr. Ingersoll Thank you.

T. Ray Andy, I have a question. What is one of the things that you're
looking forward to as the mission goes on, what are the most interesting
things that you think are coming down the line?

Dr. Ingersoll I'm very interested in the magnetic field. I really want
to settle this issue of what is the rotation rate of the inside of the
planet, because we can't really say that we know the wind speed until we
know what reference range to use. So I'm very interested in that. Later
on in the mission, when the orbit of the spacecraft tilts up and we get
some views of the night side in the northern hemisphere, I'm very
interested to see if we can see the lightning flashes. It's one thing to
see the radio emissions from the lightning, but when we are looking down
on the northern hemisphere in the darkness, from up out of the plane of
the planet, we should be able to see the lightning flashes themselves
with the camera. I'm looking forward to that. I'm also looking forward
to just getting a long time baseline on the spots, and really nailing
down their life cycles, their births, their deaths and how they come and
go, and whether they are acting as parasites on the eastward, westward
jet streams, or actually doing the reverse, helping the eastward jet
streams maintain themselves. We have ways, by watching them over time,
to answer that question too.

C. Marble Dr. Ingersoll, it's Chuck Marble here. It's nice to speak with
you. Thanks for being with us. I know it's a little bit outside of your
field but if the intense electrostatic discharges and magnetic field
around Saturn and of course the experience you had with Galileo as well.
Magnetic fields cause a lot of disruptions to Earth based satellite
communications. Have you had any communications problems with this
spacecraft or with Galileo as a result of the intense electromagnetic
fields?

Dr. Ingersoll You mean the communication link between the spacecraft and
the Earth, has it been disrupted by charged particles in the Saturnian
magnetosphere?

C. Marble Right. Does it have any effect at all, other than of course
when the spacecraft is in eclipse? Do we ever have periods where we
can't communicate or have difficulty communicating due to the intense
magnetic and electromagnetic fields?

Dr. Ingersoll I think the answer is no. On the other hand, there are
certain kinds of measurements you want to make where it's not so much
sending information encoded bits about instrument output or things. You
want to, for instance, watch the radio signal go through the atmosphere
to tell how thick is the atmosphere, how dense it is. You need to
understand all the charged particles along the entire path, and that
becomes a very tricky business. So they use several frequencies to do
it. There you do have to know about the charged particles in the
magnetosphere of Saturn, but I don't think it actually interferes with
the transmission of bits back and forth.

C. Marble Thank you very much.

T. Ray Actually, I can add one thing to that. There is one thing in the
solar system that we do know affects our communication with the
spacecraft, and that's the sun. So when the Earth is on the opposite
side of the sun from Saturn and the spacecraft is trying to send the
bits back through the solar corona, which is a highly charged field, we
actually cannot communicate with the spacecraft at that point for about
two or three days around solar conjunction. So that's just one time
where we know it does get affected.

Dr. Ingersoll You're absolutely right.

C. Marble Ham radio enthusiasts will really appreciate that. Thank you
for your time. One last question, I guess, Dr. Ingersoll, I know the
mission is still fairly young, but what's been the biggest surprise for
you as an atmospheric scientist?

Dr. Ingersoll I guess Titan. On those river channels on Titan, that's
not just a dead planet. That's a planet with real serious weather. The
polar cloud, those clouds look very much like puffy tropical
thunderstorms on Earth. They come and go on sort of similar time scales,
maybe a little more slowly evolving. All of that active meteorology on
Titan has really been an exciting thing.

C. Marble It sure has. Thanks again for being here and thanks to
everybody on the ... team for these teleconferences.

Dr. Ingersoll All right.

S. Petrus One or two more?

Dr. Ingersoll Sure.

S. Petrus This is Steve Petrus in the Strasenburgh Planetarium in
Rochester, New York. I'm trying to imagine myself flying among the cloud
tops of Saturn into the shadow of the rings. What's going to change? How
much colder will it get and what else would I see different going into
the shadow of the rings?

Dr. Ingersoll It will be dark. Of course, if you were watching the sun
it would wink out. It would be sort of like a solar eclipse, although
the rings are not perfectly opaque until you get down into the deeper
parts of the ring. So it might be a little more complicated than a solar
eclipse by the moon. The temperature will not change dramatically in a
very short time. The reason is that this is a pretty massive atmosphere,
and the sun is actually pretty weak. If you're very cold and you've got
a weak light bulb shining on you and you switch off the light, you don't
immediately get cold, because that massive atmosphere stores the heat
that it has. Another way to say it is that the time constant for
temperatures to change on Saturn is measured in years, just because the
heat fluxes out at Saturn's orbit are so small and the atmosphere is
really quite massive.

S. Petrus Is there a measurement of how much colder it is in the deep
shadow of the ring, where it's been shaded for years compared to a
sunlit part?

Dr. Ingersoll That's going to come, but I don't think we have it now.
We're sort of stuck. So far we've been stuck looking at the southern
hemisphere, which is bathed in sunlight. We're going to get a chance to
look at the northern hemisphere as we get out of the plane of Saturn's
equator. It's not going to be a big deal. I showed a slide that showed,
at least the southern hemisphere temperatures were really quite
constant, independent of latitude. I suspect that the northern
hemisphere, even though it's in shadow, it's going to look almost the
same. But we're going to measure that.

S. Petrus Thank you.

Dr. Ingersoll Sure. Anyone else out there?

T. Ray Okay, well it sounds like that's the end of the questions. Dr.
Ingersoll, we want to thank you very much for participating in the CHARM
telecon today. We really appreciate it. Everybody learned an awful lot.

Dr. Ingersoll Okay. It's my pleasure.

T. Ray We don't know exactly what the topic is for next month, folks,
we're trying to get an Enceladus talk going. We had an Enceladus fly by
a couple of weeks ago and it was really exciting. Lots of stuff
happening on the surface of Enceladus, so that's going to be our target
for April. We'll send out the e-mail and let you all know. You all have
a great evening.

M Thank you very much.

Dr. Ingersoll So long.