Transcription
All right, good morning. My name is Dave Siskind. I'm from the Naval Research Lab Space Science Division. I think I might be the second from NRL to speak here. I think Brian Wood spoke, and he represents our solar physics branch. I represent the Geospace Science and Technology branch. Our domain of research pretty much starts at the cloud tops and encompasses the middle atmosphere—stratosphere and mesosphere—that's one group. Neutral thermosphere is another group, sort of my—my little group. We have an ionosphere modeling section and then a hardware group, that with the emphasis typically on optical remote-sensing of the upper atmosphere. Okay.
So the charge was to talk about comparative upper atmospheres of the terrestrial planets, I think motivated in part by upcoming NASA missions. I mean, typically you think of that as Earth, Venus, and Mars, and motivated by upcoming NASA missions, I'm really gonna focus more on Mars and Earth. That's just stuff we've been working on. There are two parts to the talk, and we'll have a break. The first part is more of what I would call a one-dimensional view of upper atmospheres. We'll look at composition, chemistry, thermal structure, its variability due to solar effects, anthropogenic effects—so far as far as we know, Earth is the only planet that has anthropogenic long-term effects. Mars has dust. The thing with the 1D approach is that all the dynamics, the meteorological—meteorological variability is parameterized away, and we'll talk about what that—what that is.
Then the second part, we'll look more at the 3D variability, and the emphasis really will be lower atmospheric effects on the upper atmosphere: the whole spectrum of dynamical disturbances, planetary scale waves, tidal oscillations, small-scale gravity waves. I believe you've had a fair amount of discussion of electrodynamical effects, so I'm really just gonna superficially touch on that here, only because there's now a lot of evidence that neutral atmospheric variability coming from below can affect the electrodynamics, so we should at least touch on that.
Just to summarize where a lot of the data comes from: the composition data—and for the Earth, there's just too many datasets to—to really go through—is ground-based, satellite. I really just want to just talk about the planetary—the composition data for Mars that the United States has is very old, and as some spectra taken from Mariner 9 and some in situ samples from the Landers on Viking 1 and 2. Dating back to the early to mid-70s, and then for 20 years there was nothing. Starting in the mid-90s, there's a slew of missions, really more focused on a lower atmosphere and the surface, but to achieve a circular orbit what they'll do is they'll dip deep down into the thermosphere and use the—the atmospheric drag to help circularize the orbit, and these aerobraking maneuvers and the variations in the thermosphere density that we have observed have provided a lot of data, and I'll be showing the aerobraking results. There is some composition data from the European Mars Express. The Europeans have a Venus flavor of that as well, Venus Express. In the late 70s into the 80s, there was a fair amount of composition data taken from the Pioneer Venus mission.
Now, as I said, a lot of what I'm going to talk about is motivated by upcoming NASA missions, of which there were three. The Ionosphere Connections Explorer will be in low-Earth orbit; it'll be in a low inclination, and so it's really gonna be focusing on the tropics, in the lowest—the low to mid-latitudes specifically to look at the effect of thermosphere winds and the ionospheric response. That's gonna be scheduled for 2017 launch. Another satellite scheduled for 2017 launch is GOLD, and that's going to be in a geostationary orbit, so they'll be able to take more high time resolution images of the entire upper atmosphere to be able to look at dynamical variability on timescales more rapid than a typical orbital period. And then finally, there's MAVEN. MAVEN is gonna really focus intensively on the Martian thermosphere and ionosphere with the ultimate goal to address the question as to how did Mars lose its atmosphere over geologic time. MAVEN is on its way, and it will arrive at Mars in a few months, and so we're—we're involved in these missions, and I think that really is what guided what I was going to talk about. You'll see a lot of references to models in the talk, and patterning the—the—the two halves—the lecture, there's two categories I'll be talking about: sort of the global mean one-dimensional models where they're very flexible—again, the dynamics is all parameterized away, but you can really play a lot of games with them; you can really do a lot of sensitivity studies to learn about particularly chemistry and thermal effects. These were pioneered by Ray Roble in the late 1980s in NCAR, and then Steve Booker expanded that to encompass Venus and Mars. And I should acknowledge Steve because he has given me some—some of his slides, and some of the work in here is stuff that he's done. He was of great help in putting this talk together.
Then there are the general circulation models where you don't have the parameterizations, or you have fewer, and you're beginning to resolve, at least depending on the gridding of your computer model, some of the large-scale dynamics. There's a whole slew with different acronyms; typically they end in GCM for general circulation model. There's the Community—the WACCM—Community Climate Model, some Mars flavors. This last one at the bottom is a little different than the ones above because this is a weather forecast model: there's the Navy's operational weather model. Up until very recently, they've renamed it; they've changed—changed a few things, but what we did is we—we extended the top of the model, which pretty much did the surface to the lower stratosphere; we pushed the lid up to the edge of space to about 95 kilometers. The idea is that then you have the top of that model can be forcing functions for the bottom of some of these thermosphere ionosphere models, so it's a way to transmit information—whether real weather—from the lower atmosphere to the upper atmosphere. And I'm going to talk about—are the trials and tribulations of how we—of what happened when we did that.
I think ultimately probably the goal of the—of my presentation is for people, when all is said and done, to look at a slide like this, which just lays out some of the fundamental planetary parameters for Venus, Earth, and Mars, and to be able to comment as to what some of these implications—the implications of some of these parameters are for the thermosphere and atmosphere of the different planets. And so we'll—we'll hopefully we'll cover all these. Obviously, the gravity is different. Mars is the—is the outlier there with the weakest gravity. We'll talk about the scale heights of the—of the planets. Obviously, there are different distances from the Sun, and Mars is a little unique in that it's got a much more eccentric orbit, so its distance varies more. Perihelion is when you typically get the bigger dust storms. They're obviously different sizes, and they rotate differently. Well, the Earth and Mars pretty much have the same rotational frequency. Venus really doesn't rotate in a significant way. What that means is that the Coriolis parameter for Earth and Mars is the same, and Venus it's completely—it's—it's not a factor, and that affects the dynamics. Seasons—Venus again is the outlier. Earth and Mars have pretty much similar seasons. So between the seasonal similarity and the Coriolis effect, there is a fair amount of similarity to some of the—the progression of the seasons and the meteorological variability in the Earth and Mars, even though, of course, Mars doesn't have all the water that Earth does. In terms of magnetic fields, Earth is the big outlier; they're the only one with a real complete dipole magnetic field with—with an aurora, but there is some residual magnetism on Mars, and we'll talk about that a little bit. Finally, this is really a very derived parameter; it's not a fundamental planetary parameter, but we'll talk about this. This is a measure of how the upper atmosphere is heated up, and you know, you can imagine if you send in all the cyanide and radiation from the Sun and it just radiates away, well that's a low heat efficiency, but if it drives exothermic chemistry and that releases heat, then you have a higher heating efficiency, and—and that's where the Earth stands out, whereas these other planets, dominated as they are by CO2, they radiate a lot of what they—of what comes in. Let's say I'll skip this.
So let's just start, as I said, I really like to think of this as coming from the ground up, so let's start at the ground. Both planets have mountains. By one important point is that the mountains on Mars are almost three times the size as the highest peaks on the Earth. Now you might say, well, that's not fair; the Earth's—it's got, you know, if you took away the oceans, you'd have the ocean floor, and if you really did from the bottom of the ocean to the top of Mount Everest, you'd get a bigger number, and actually you wouldn't. I mean, that would give you another ten, eleven kilometers; you'd still be short of 25 kilometers. But from the standpoint of meteorology, what really counts is where the surfaces, because these mountains are obstacles to wind flow, and so the fact that the Earth's half the topography is covered by seawater, it is important that the Earth has nine-kilometer-high obstacles, and Mars has 25—25-kilometer-high obstacles to the tropospheric wind flow. I will admit this is not a real photo; this is a computer-generated from topographic data.
Okay, so we'll start at the surface; we'll move up in altitude. Obviously, the atmosphere, the density and the pressure go down, and I want to talk a little bit about how the density is changing with height, and just what are some of the differences. So this is a grand plot going from the ground to about a thousand kilometers. There are two curves spanning like 14 orders of magnitude in mass density. The blue is the Earth, and this purplish thing is Mars, and what you should see is right at the bottom there's about a two-order-of-magnitude difference in mass density, and if you look carefully you can see it looks like these curves converge. So I want to talk about that, just focusing on the atmosphere up to 100 kilometers. So you see that the densities here are different, but up here they've become much closer together, and the question I would just ask from the standpoint of maybe getting to jog your memories for some of the homework assignments you had is why is there this convergence such that by the base of the thermosphere the densities are not that different, where is it the surface they differ by over two orders of magnitude? So if people want to throw out any—anything you might remember from the homework, what is the—if you see these slopes, what—what really governs the decrease in an atmospheric density as you move up in altitude? What's the—you know, it varies exponentially, and the factor that controls that exponential is the—anybody? Scale height, right? So, in case people don't remember it all, so it's constant times the temperature. So Martian gravity is 40%, 38% of the Earth, so right away Mars' scale height is gonna be bigger; its density, all else being equal, density will fall off more slowly in the Martian atmosphere. Now some of that you get back because the Earth's mass—mean mass—is governed by N2 and O2; CO2 is 50 percent heavier, so it sort of counteracts the—the factor of two and a half you get from the density a little bit, and then also the numerator is not quite the same because Mars is colder—about 70, 80 percent the temperature of the Earth. If the Earth's middle atmosphere averages about 220 or so, Mars is like 180 or whatever, but fundamentally the—the scale height is different. So I know you've had these equations in other classes and in the homework, and so this just sort of summarized what I was saying is that in the end the scale height for Mars, when all is said and done, is bigger than the Earth's. As you go from the ground to 100 kilometers on Mars, you're maybe going through about 10 or 11 scale heights, and on the Earth you're going through about 14 or 15 scale heights. That three scale height difference—e to the minus three—is about a factor of about 25 or so, and that you can see sort of accounts for the convergence of densities. Now, if you just look on the right for a second, there is an additional effect: is the periodic dust storms. I can't see the curve, so Chloe, they're supposed to be one of them. Dust acts to heat the Martian middle atmosphere, and when it does that it puffs the atmosphere out a bit, and so the point was supposed to be that during dust storms the density at 100 kilometers is actually becomes much closer to Earth's density due to this sort of artificial—not artificial, but the inflating effects of dust. Meaning the other point is that again you can't really see that—hopefully when you look online you can see it—that the differences in density due to dust go away by 100—up to 150 kilometers or so. There's a recent model result, and that explains something because the guys who do the aerobraking didn't understand what the fuss was with dust storms—like we don't see any effect from—on the aerobraking whether it's dusty or not. The aerobraking typically is down to about 150 kilometers, and so the model results sort of explained that is like, well, it's—it's—it's gone by that altitude. There is also, just as a fun factor, for some people who are really trying to look at—to see if they can see meteors burning up in the Martian atmosphere from maybe some of the ground-based imagery and looking at the densities on Earth. Meteors burn up between about 85 and 100 kilometers when the density is around 10 to the minus 6, so on Mars you see that would be between 70 and 80, but other than that, meteors should burn up on the Martian mesosphere just like they do on the terrestrial mesosphere. That's sort of an area—it's not a lot of data on that. Okay.
So now we can go to the upper atmosphere. This is a plot where we—on Earth—go up to 500 kilometers; on Mars, going up to 320 kilometers, and now I've broken it out by the composition of the major gases. Both atmospheres convert from a relatively heavy gas like N2 or CO2 to a lighter gas such as O, and that's again related to the different scale heights. The lighter gases have a lighter scale height. There is one point that is going to come back a couple of times, and I want to point it out—start pointing it out now so we can start thinking about it. If you look over here, you see that the O and the CO2 and the CO—I'm sorry—track the CO2, and then you get a break here at about 120 kilometers where the O and CO2—I'm sorry, the O and the carbon monoxide—vary with this larger scale height. So the Martian composition is invariant up to about 120 kilometers, whereas on the Earth, pretty much below 100—starting at 95 kilometers—the light atom—the O—never really has this tracking of the N2; it's already increasing with its own scale height. So what we say is that the homopause—the altitude where the atmosphere begins to differentiate in composition—is different between the two planets. All right. And so we're going to talk about that several times for the rest of—the rest of the talk.
The first thing we need to understand—we want to understand what the homopause is all about—what governs it—is the two different types of diffusion: molecular diffusion—species dependent—separate scale heights for each gas. Molecular diffusion increases with altitude because there's a 1 over N, and so the scale height is always gonna be double that of O2 and N2 and triple that of CO2. The other kind of diffusion is so-called eddy diffusion, which is considered to be like bulk mixing—ah—containing a lot of lower atmospheric motion, turbulence, and as when these two are equal, that's the definition of the homopause. There's really not—it's not fair to call it an altitude; it's really a region because, as we'll discuss, eddy diffusion varies all over the place, and molecular diffusion is sort of different for each gas, so there's—we call it a homopause region, but the point is that D is fixed by basic kinetics; K is much harder to estimate, and I think over the last 50 years there's been a lot of trees killed to generate the papers discussing what K should be for the Earth's middle atmosphere and lower thermosphere. It's also—as you'll see—less data, but this has been a subject of interest from Mars as well. Now, when you look at a 1D model, since you don't resolve much of dynamics, all of meteorology gets swept up in K. K is really a tensor, so we typically call it Kzz for the straight vertical transport. Now the newer 3D models resolve more—what we're finding is that you don't need quite the high K; you can use lower K, but there's still stuff you don't resolve like small-scale turbulence, which again is very poorly constrained.
So here's a model calculation to show the homopause on the Earth. All right, this is again using one of the—those 1D global mean models from Ray Roble. I've got a bunch of calculations I've done with them too because it's very easy to use. So here's a representative K profile for the Earth; units are meter squared per second. This is going from 50 to 200; peak of about 10 to the 6 somewheres between 80 and 90 kilometers, and here is a molecular diffusion coefficient for O in N2 atmosphere, and you see where they cross is about 90, 95 kilometers, and that's roughly the homopause on Earth. Now, estimates of K on Mars vary by about an order of magnitude, but they are uniformly larger—about 10 to 50 times larger. So if you ignore for the fact that I really should have shown you from Mars—O and a CO2 atmosphere—that's not going to be more than a 50% difference, and you look at where the molecular diffusion coefficient intersects the Martian range of eddy diffusion, you see it's at a higher altitude, so it sort of makes sense that the homopause on Mars is up here—between 120, 130 kilometers—and on Earth it's down around 95 or 100. Now that's governed by the variation in composition from Mars, anyway. One of MAVEN's main objectives is to really scope this out, but getting—looking at the atomic oxygen and—and the carbon dioxide, and they're actually going to do some dipping to get down to these altitudes to try and sample it. So this is K—is—you see there's an order of magnitude variation from what we think it is on Mars, and the composition is still not totally—it's not that well-documented, but what we're gonna want to talk about is why K is so much bigger on Mars than on Earth, and so we'll come to that again. This is—we're just sort of beginning to work our way through this.
Now it's interesting to ask what happens if you change K, or if K varies, and so this is easily done in a global mean model, and so I did that. I lowered it starting here. Now remember, it only really matters in here because up here, yeah, there's a big difference in K, but it's all molecular diffusion, so it's really—I changed it by a factor of four in around the turbopause region to slightly change the altitude of the turbopause. Homopause—they're synonymous, so I apologize—so if I've been using those interchangeably. What you see is that the composition is affected at all altitudes up to—well—up into the thermosphere, and by lowering K we've increased atomic oxygen at all altitudes, and that's because it's more free; molecular diffusion takes over, and uh—it—that—that change in the bottom boundary condition diffuses all the way up. That affects the ionosphere. So on Earth, O+ is the dominant ion; if you change the O at those altitudes at the expense of some of the molecular species, you're gonna increase the O+, and since the electron density is the sum of all the ions, changing K at the 95 and 100 kilometers changes the peak electron density of the Earth's ionosphere. So to understand variability, and this is the fundamental sort of philosophical basis for a lot of what I'm going to talk about—in what I've been doing—is to understand variations in the peak electron density, you really need to consider the bottom boundary conditions at the base of the thermosphere where the atmosphere is going from well-mixed to diffusive equilibrium. So the link is: decreasing Kzz increases O at the homopause, gives you a higher ratio of atomic to molecular species. We'll talk about this in a second when I look at the chemistry. More O+, greater electron density. Now this figure is taken from
One of the earlier papers in the textbook series that I think you've been using, I just want to make up just a couple of comments. It shows the inputs at the top, which is the initial sort of ionizations of the primary ions. This is really a graphical indicator of ionization chemical potential energy. So N2 is takes more energy to ionize, an O+ takes the least. So that ion chemical reactions of with an O+, you're not gonna I announced it; it's just going to recombine. So recombination to neutrals occurs at the bottom; input ionization or at the top. And so the terminal ions are down here, and the primary ions are up there. And it's interesting on Mars; this is actually the dominant ion and the entire ionosphere, which is sort of ironic because there's no O2. So you have to be a little careful if you want to understand the composition of an atmosphere and say, well, as their oxygen is their life, don't look at ionosphere at composition because that could mislead you.
Okay. Now the effect of changing the KZZ enters in through the dissociative recombination. So if you are increasing the molecular species, then this reaction of O+ with N2 is going to go more rapidly, and once you make NO+, that recombines very quickly. So it's the where is if you don't have a lot of N2 and you have more atomic oxygen, O+ on its own doesn't recombine very quickly; it's got to have N2 to recombine. And then on Mars, the equivalent reaction is O2+ + electrons. It's worth noting that these recombination reactions vary inversely as temperature. So if you increase the temperature, you'll slow these down, and you should see an increase in electron density. And I'll show you an example of that on Mars. So just change the electron density; you can change the Sun, which changes the inputs; you can change the composition, the molecular atomic to molecular species, which is what the KZZ change did; or you can change the temperature. I'll show some examples.
Ah, this is just a comparison of the ionosphere of Earth and Mars. Mars has what we call an F1 ionosphere; it doesn't have all this high-altitude O+, which on Earth can flow in in the presence of the magnetic field. So it doesn't have this dynamical region where you have all this complicated electrodynamics that you have on Earth. Instead, if you look at the F1, the chemically dominated region, which is a peak of about 10 to the 5 at 150, you see that Mars looks kind of like that. So it's a chemically dominated ionosphere. This is just some more detailed summaries. We have some data for Venus; we've got an empirical model for the Earth, which is a summary of lots and lots of data; and then from Mars, there's some data, but really is a model result. And this is what Maven is gonna be looking to to change to populate that with real data. It's probably can't even see the species, but this is O2+ here; this is O2+ on Venus. Earth he's got this big old plus bulge, and then down low you have the molecular ions.
One thing that was a little interesting is uh when Mariner 9 got to Mars and was measuring the electron density, and it should normally rise and set with the Sun due to this changing zenith angle, there was a population that was sort of anomalous. And this was during the global dust storm. And again, although you couldn't really see it on that other slide, the idea that the dust puffs up the middle atmosphere due to heating will get transmitted to the height of the Martian F1 peak. So instead of peaking at 120-130, it was about 130 to 140 kilometers; it's about 10 kilometers higher. And as the dust decayed, they showed a fairly monotonic decay in the altitude of the ionospheric peak, going from September 1971 to January 1972.
All right. So to summarize to this point, we've discussed the lower-middle atmosphere up to the homopause; that the homopause altitude is different between the two planets; how conditions at the homopause infect the entire thermosphere and ionosphere; very briefly some of the chemistry; and now we're going to consider the densities above 100 kilometers. And here you see that they diverge, so that the Earth falls off more slowly than the Martian thermosphere, and that again comes back to the scale height. Now we're not thinking of gravity so much, but we're thinking about temperature; temperatures bigger, the scale heights bigger; and we're thinking about mean mass. So here are a lot of three thermospheres: Venus on the left, Earth and Mars on the center and right. There is a just as I was talking about the homopause for composition, maybe an analogous key altitude for the thermal structure is the mesopause, which is the temperature minimum above which the temperatures increase. And you see that is different on all three planets. You see that the if you look, I since you probably couldn't see this, I just put the scales in red, you know the temperature in Earth at solar maximum is up over a thousand Kelvin, much higher than any of the other planets. This is the solar minimum values, and the - curve Mars seems to come in second place, and Venus is the coldest. And also if you look carefully, and we'll talk about this a little bit, the variation on Earth from solar min to max is greater than the other planets. So we have sort of three differences in thermosphere temperature profiles: peak temperature, solar cycle amplitude, and mesopause altitude; Earth is the lowest, Mars is in the middle, Venus is the highest.
Now, as I said, it really wasn't going to get into much detail on Venus, but there is one sort of fun thing to to know, which is since Venus doesn't rotate, the night side of Venus in the upper atmosphere where the CO2 can just radiate to space gets very cold, and it's actually not a thermosphere; it's called the cryosphere. This is a model simulation: local time noon, local time 2400, so midnight. And you see there's no mesopause; maybe that's the mesopause, I'm not sure, but this is 110 Kelvin all the way up. So Venus has got this huge day/night contrast in the thermospheric temperature.
All right. So to understand the differences in the mesopause, the differences in the solar cycle effects and the amplitude, got to look a little bit at the heating and cooling. May be hard to follow the spaghetti curves here, but both of these are altitude profiles with a heating rate on the x-axis. The rightmost curve is the total heating, and the point is the absorption of the EUV and and the Forel to violet that drive the heating for the upper atmospheres is relatively high up, and I'll tell you what relatively means in a second. Okay. The cooling is down low where the CO2 can radiate away. So this is this gap in altitude between heating up here and cooling down there, and so there's conduction; it's kind of like just the transport via thermal conduction from the source region to the sink region. Okay. Where that sink region is depends upon how much CO2 there is and the and and and because the the reaction that defines the cooling is the emission of CO2 at fifteen microns after it's been vibrationally excited by collisions with atomic oxygen. All right. This is the least efficient on the Earth because the Earth doesn't have a lot of CO2, so the conduction has really got a long sort of a long way to go until there's enough CO2 that radiates away the thermospherically. So that's why the mesopause on Earth is the lowest altitude of the other planets. Differences between Venus and Mars a little more subtle, depends on the ratio of O2 CO2, and in any event we're really not so sure what the O is on Mars anyway, so there's probably gonna be some refinement there. There is some observations though to support the idea that Mars is in between Venus and the Earth in terms of its ability to radiate away the thermosphere of heat. So the other point is that the Earth has this all this atomic oxygen that is inefficient at radiating and instead it participates in exothermic chemistry which releases heat. So this is sort of why that heating efficiency was greater for the Earth than from Mars and Venus; it has to do with the composition. So the Earth has a greater heating efficiency; the cooling is a long way away; it's got to have more thermal conduction; and so it's just if heats up more, it responds more to solar activity; it's got the lowest mesopause.
From some of the arrow breaking data, which is measurement of thermospheric density during periods when the Sun was variable, we can get a sense of how the density varies in response to solar forcing. And from the density variability using scale Heights, we can back out the temperature. And this plot here is probably too complicated to get into the details. I've tried to summarize it here. The Delta F is solar flux in terms of the F 10-7 radial index, which is a measure of solar activity. So what Geoff Forbes showed was that the temperature change in the Earth is much greater for a given change in solar flux; Mars is in between, and Venus is the least. So again, Earth has the greatest heating efficiency, or alternatively you could say it's the greatest cooling inefficiency, okay, because isn't anything to radiate away until you get down to very low altitudes. There is one exception to that though; there is another molecule in the Earth's thermosphere that does radiating infrared. Now I mean homospheric almost homonuclear molecules, I go to an N2 don't radiate; there is nitric oxide in the Earth's thermosphere that does radiate. Nitric oxide is a little complicated though because it's a trace constituent; it's very variable, and it actually is produced by solar activity. So what the green is just to sort of highlight the profile so you can see it to compare it to the CO2, and you see above about 120-130, depending on solar activity, the nitric oxide will dominate the CO2 and it will be a secondary way of radiating heat, but it's really only effective at solar maximum; at solar minimum there isn't enough NNO to do it. So that's why I said Earth is all CO2 it's solar main, some nitric oxide at solar max. I'll skip this slide, but this is just observations sort of supporting that this idea that that the Earth is all CO2 with solar min and some and all its solar max is important. We want to look at global change because CO2 is increasing on the Earth, and we have observed that from a Canadian atmospheric chemistry experiment over about eight years. This is it's showing both carbon monoxide, carbon dioxide, and the total carbon because there's some chemistry here that partitions it, and the point is it's been going up pretty steadily over eight years, actually going on more than we expected. So that's going to increase the cooling efficiency of the Earth's thermosphere; it's just more CO2, but that's only gonna be most effective at solar minimum because you don't have the nitric oxide. So did they loot it? These are some calculations I did showing the I double the CO2 and one of these little 1D models to show the change in temperature, and the change is bigger for the low solar activity calculation than the high solar activity calculation. So this means is that global change in the Earth's thermosphere at present is primarily a solar minimum phenomena, and that's been observed. As I said this when I reviewed datasets, I said it's almost too much to go into on the Earth. This is sort of an example of that from a catalog of several thousand orbiting objects in the Earth's atmosphere. John Emirate and colleagues have derived thermosphere densities over the last 40 years or so, and you see that the density varies with solar activity; this is solar activity down here, the F 10 7, and you see that there at the top it's hard to say because it's tracking the solar cycle; the bottom where the solar activity is sort of the same, you see that each solar minimum the density gets less and less; this actually got a lot less, and this was still the subject of some controversy, but even before the recent extended solar minimum you could see that the solar minima the Earth's thermosphere was getting thinner, and that's got implications for the lifetime of satellites and and but it right now it seems to be a solar minimum phenomena because nitric oxide dilutes at at solar maximum.
Okay. So the summary to this point is we really completed the 1D global mean discussion. All right. We looked at atmospheric density and composition coupling to the ionosphere; on the Earth it's the ratio of atomic to molecular species, in this case O/DA and 2, and it's linkage to the electron density; the analogy for Mars is O2 CO2, but again this is we'll know more about that in a couple of years when we start looking at the data, go get the results in thermal structures depends on the efficiency of CO2 cooling on the three planets, and that has implications for the reactions of solar forcing, anthropogenic global change. So now what I want to do just before the break in a couple of minutes, I want to start by looking at 3D variability. Okay. So we're gonna try and get away from the very highly parameterized dynamics all bundled up in this case easy parameter and seeing well what's really going on. All right. So there were two current approaches to modeling, and I touched on this a little bit when I went through some of the acronyms: seamless or coupled. Seamless, as exemplified most notably by the WACCM model run by NCAR, developed and run by NCAR, is a model that goes from the ground all the way up to the exobase in one single dynamical system. Okay. And this for doing self-consistent climate calculations is the way to go because you can change CO2; you can look at global warming on one hand, you looking thermosphere at global cooling on the other hand; you can do the whole thing self-consistently; you can release methane from industrial activity in the troposphere, and you can see its effect on the thermosphere, and you get all the meteorology, coal variability at the same time. I've been working with the coupled approach, which is taking no gaps alpha up to 95 kilometers and using that to force the one of the thermosphere ionosphere electrodynamic GCMs. And here you can do case studies because you take the weather on a certain day and you can drive the model, and you can see what the thermosphere and ionosphere might have been on that day because we we've produced some analyses for specific days, specific months going up to the mesopause. Okay. So we're gonna look at what happened to the atmosphere when we put in realistic meteorological variability at the base of the thermosphere. So on the left is what I call the standard boundary condition using the NCAR migrating tide model; we'll talk tides you know in a half hour or so; suffice it to say that at this pressure which is about 95 kilometers, this is temperature; you see that's pretty smooth; there is some wave, this is longitude, sort of two waves on this latitude circle here; that's a semi-diurnal tide of a maybe 10-20 Kelvin at about between 30 and 45 north; this is the G potential height field; again it's also pretty smooth; this is for January 1st, 2010. What no gaps alpha says is the real meteorological field, okay, based on assimilating lower and middle atmospheric observations in a data analysis system. First of all, the temperature varies with latitude because the the mesopause is cold; second of all, you see the variability is more pronounced, and even more so when you look at the actual heights, which is the measure the altitude of a given pressure surface; it's very blotchy, and this is not noise; this is this is real; this is really what's going on. Okay. So we're going to compare the calculated thermospheric ionosphere using this versus using this; we were very excited, and we can compare it with this data; this is data; this is radio occultation data from a Taiwanese satellite; time we need is an American collaboration called COSMIC; the it's longitude versus latitude; the red is the peak electron density; so it's roughly about 10 to the 6th; I think you've already talked a bit why the Earth's ionosphere appears as two stripes straddling across the magnetic equator; we'll talk a little bit more about that in the second part of the talk. So this is the data, and this is what we had with the old model, which wasn't bad; you see the color schemes the same red to red; see the stripes; here's the new model, realistic boundary forcing, and it's junk; we broke it; what went wrong? Took us about a month to figure out; you've got fifteen or twenty minutes, but you're younger, you'll figure it out, but in thinking about, and we'll come back and talk about it, you may not probably get the whole answer, but what tests should we look at in your model to try and track it down? Okay. And that's what I'd like you to think about, and so we'll take a break now, and we'll come back.