Transcription
Okay, wonderful. Um, welcome everyone. Thanks for coming back from lunch. My name is Lauren Blum. I'm a professor here at CU Boulder. Um, I am up next on your agenda to talk about the magnetosphere-ionosphere system. Uh, this is pretty broad. I'm supposed to cover quite a lot in um, not infinite amounts of time, and so I tried to touch on kind of things I found interesting. Um, I know it's a pretty broad group of of um, attendees also, and so some of you might be experts in some of it. Um, feel free to to chip in on those topics, and then some of you might have never seen some of aspects, and so feel free to ask the, you know, most basic simple questions too. Um, any general announcements, or we'll just start? Cool. Okay, wonderful.
Um, so a teeny bit more about myself. Um, I work here at CU Boulder in the astrophysics and planetary sciences department, but also at the lab for atmospheric and space physics, or LASP. Um, I was born and raised in New York City, so Boulder is really like the countryside countryside for me, very rural. Um, uh, I studied physics in undergrad. Um, took a year off to work at Los Alamos before going to grad school to kind of figure out if I wanted to go to grad school. Um, um, I ended up getting my PhD from here in the aerospace engineering department. Um, even though I kind of came from science and have continued in science. Um, after that, worked at Berkeley briefly and then at NASA Goddard for a little while, and then I moved back here. Um, summer of 2020, hindsight not the best time to move back here, but really deep mid-pandemic, came back here for an assistant professor position at Boulder. Um, my research is focused on planetary magnetospheres and particularly Earth's magnetosphere. Um, energetic particle dynamics uh in the radiation belts here at Earth, and then I come at this from kind of an observational and instrumentation perspective, so building energetic particle detectors um for cubesat and smallsat missions, and you'll see some of these biases probably come out in this talk. Um, both the Earth earth-based um magnetospheric leaning and then also the kind of more observational perspective I'm, you know, really interested in how we actually measure some of these things we know about the system and and um how we figure that out from an observational perspective, not just from the fundamental physics. Okay.
Um, I think this is an older version of my talk because I uploaded it yesterday so that I would obey um, obey wishes, but then again this morning I can use this version if that's the easiest, but if there is um, a quick way to update it, that might be smoother. Yeah, this one looks great. Thank you. Okay. Um, okay, so um, today we're talking about planetary magnetospheres and ionospheres, and I did look at the rest of your um speakers, and and it looks like Bob Marshall is going to talk about ionospheres in quite a lot of depth, and he was really on top of things and uploaded his slides, and so I skim through them, and so I'll mostly focus on magnetospheres and touch a little bit on ionospheres as well, but I didn't want too much overlap there. Um, so we'll talk about what they are, what they look like, kind of the parts that make them up, and then also how they behave. Um, we'll really primarily focus at Earth. Oop, I'm practicing this fancy pointer, see if I keep using it. Um, but then I think throughout the talk, try to keep in mind how this would vary in other systems, what this looks like at other planets or in other stellar planetary systems. Um, and what happens, you know, when you change some of the variables of our system, if you change planet size, mass, rotation rate, solar wind driver, what what is that do to the system? And like I said, um, I like to think about how we actually observe these regions and processes, how do we know what we know about the system? Um, and then I also wanted to focus and highlight a bit on kind of the interfaces and cross-region coupling, so I, you know, people sometimes say, oh, I'm a magnetospheric physicist, I'm a solar wind, I'm an ionosphere person. Um, but uh, there's a lot of overlap between these, and the system is very interconnected, and so understanding the kind of um, uh, coupling across these regions is really important, and because I think the theme of your um, this year's summer school is comparative um systems, I thought I'd focus a bit on comparative magnetospheres here, and um, there's this quote now from a while ago, but the um geospace environment modeling workshop, GEM workshop in 2010, um, where Margie Kivelson, a planetary scientist, um, talks about kind of why you want to study comparative magnetospheres, and typical of the rigor of physics is the need to change the parameters governing the system studied in order to test whether behavior varies as predicted, and so you know, as as experimental scientists, we want to turn a knob and see if we know what will happen, and that's difficult to do in space. Um, you know, you can't actually go out and change um the magnetic field strength of Earth, but you can find systems that have different variables, and and through that both um, uh, better understand the process going on at Earth, you know, do you really understand what's going on if you can you predict it if you change something? Um, and then also use what we know about the Earth-Sun system to understand other planets and and exoplanets or or stellar planetary systems. Okay.
That being said, I'm gonna like um, do exactly what I said not to do and and pigeonhole all of you, but I kind of wanted to get a sense of what everyone studies and works on, and um, again you'll see some of my bias that I lumped solar and solar wind together here but gave Earth's magnetosphere its own bullet, but I just wanted to get kind of a quick show of hands of who studies what, and you can raise your hand multiple times if you think your research really um, you know, includes multiple areas here: so solar, solar wind. Lots. Okay, great. Um, Earth's magnetosphere. Okay, cool. Um, Earth's ionosphere, atmosphere here lower down. Great. Um, how about other planetary systems? Okay. Okay, nice. And any others that I didn't actually cover on here? I didn't want like a million bullets, but everyone raise their hand at least once. Okay, wonderful.
Um, I also, instead of just talking at you forever, I wanted to start with a quick little discussion on, you know, why um, should you, and whatever your specific research area interests are, um, learn about some of these other regions, and so I'd ask all of you to kind of think about what your research is, think about either from that list I had up there or general space environment, what's another region that's kind of seemingly unrelated, and think about, you know, why should you um care about it deeply and how might it impact your own research? And so I do this a lot, especially for this talk. Um, sometimes people talk about the ionosphere, and I just kind of blaze over, and there's lots of different um, you know, molecules and different uh things that I don't want to know about, and then I try to think about how it relates to magnetospheric research and the radiation belts, for example. So I'd say chat with your neighbors for like two minutes. Um, uh, talk about what your research is, pick a different topic, and why it's not so far and unrelated as it might seem, and then um, I'd like to hear a little bit about what you discussed. So take a few minutes. Okay.
Um, I know you can all talk about this for, you know, the next hour, um, but we'll bring it back in, and I'd love to hear, you know, if anything came up in your conversations, any connections that you made um, or didn't make. Yeah, does anyone want to share? Thanks. Um, one thing that we talked about is that, you know, a lot of these different subfields within space weather, whether it's magnetosphere, ionosphere, um, whatever, you know, we all use similar techniques but in different ways. A lot of the problems are the same, but they're specialized to the field that we're in. So like I was at KP, and I do stuff with the aurora, and I was um, actually in a solar flare talk, and the technique they were using to analyze these solar flare ribbons, there's like these little beads that form sometimes right before the flare onset, is the same technique used to work on auroral beads. I thought that was really cool. So that is that's a great point, not just um, how does the science connect, but how do the techniques we use really, you know, medical imaging versus solar imaging. Yeah, cool. Did you I think we're supposed to to pass or toss this little thing? Yeah, thank you. So uh, it's about uh, for the magnetosphere, there are the two sources of the charge particle that's are coming, one is sun and other is our ionosphere, so it's either, and everything in uh magnetosphere is matter for us, whether it's low energy electrons or it's high energy electrons, so that's why. Yeah, great. I'll I'll have um a few slides that kind of repeat that, the sources of what's filling our magnetosphere and where they come from, and I think um, keep in mind, you know, at Earth like you said, solar wind and ionosphere, but at other planets it might be different. Yeah. Um, anyone else? And if you're somebody who hasn't used the box yet, maybe you should volunteer. Don't have to though. Um, yeah, great. Thanks. Hi. Um, um, well, I was once reading a book about the solar physics and atmospheric physics, and they in the book they made an idea that by studying the earth atmosphere, it's a very good analogy or as an introduction to study the solar atmosphere because there's some layers of of both atmospheres that are partially ionized, not completely ionized. Yeah, excellent. Okay, thanks so much. Um, uh, we'll keep moving, but I I liked a few of the things I heard, you know, both about how the the physical processes interact, also how our techniques overlap, and then over at this table there was some discussion of like, you know, even if you're studying the sun and it doesn't actually it's not affected by Earth's ionosphere, that might be how you can sell your science or motivate it and make it more interesting to, you know, what's actually important about solar physics that is important to ionospheric scientists. So I liked that um, uh, way of thinking as well. Okay, so thank you again um for sharing a few notes as we move forward. Please interrupt at any point. Um, I would much rather hear from you all than just talk at you for forever. Um, questions, comments, things you know about from your own research, if you're an expert on something we're talking about. Um, and then my hope again throughout this whole program is that you'll learn a lot from each other, not just um myself or the speakers that you have. Um, and then the other thing to keep in mind that actually um Fran mentioned to me was kind of as we go through this, think about what the common um questions or misconceptions might be about some of these systems, and so as I've taught some of the kind of intro undergrad courses here at Boulder, I always like it because um students come up with questions and you're like, oh, I didn't even realize that that's like what you would assume. Um, and so like like space is empty, and I'm like, oh no, there's all these interesting particles filling it, but that's kind of what you hear about, and and so um, please think about that as we go through. Add any that come to mind, and then um, also, you know, if you've never understood something, please jump in. So another one that's kind of more um, I get from grad students a lot is that um Earth's radiation belts, that that the particles come all from the solar wind, that these kind of high energy particles come directly from the Sun, enter the magnetosphere, and make these um regions of very high energy particles, and it's not quite that direct. The particles kind of circulate through the system for quite a while. Um, can be from the ionosphere or solar wind and get energized through a whole number of different processes on different time scales. Okay, so um, yes, I hope to hear from you throughout the next hour. So I thought I'd start with kind of very general definitions. Um, what is a magnetosphere? And if you look this up, um, one of the ones that you often get is that it's this volume of space that's carved out of the solar wind um by the planet's magnetic field, formed by the interaction of flowing plasma with a magnetized body. Um, does anyone see any modifications we might want to make to this definition just right off the bat? Yeah. Yeah. Yeah, wonderful. So this assumes that the the planet has an internal magnetic field, but we often talk about magnetospheric dynamics of induced magnetospheres, um, things like uh, you know, or um systems like Mars which don't have a a global magnetic field but little crustal ones. Um, and so even this basic definition we might revisit or or modify depending on what system we're talking about, but at Earth the magnetosphere is really dominated by two two um, uh, influences: the internal magnetic field generated by dynamo processes inside the core, and I think you'll have a number more lectures on actual dynamo physics and how this happens both at different planets and stars. Um, and at Earth this is roughly dipolar, a dipolar magnetic field. Um, but it is important to note it's um magnetic field is offset from the Earth's center and tilted from relative to the spin axis. So this actually introduces lots of uh details um to the solar wind-magnetosphere interaction, magnetosphere-ionosphere-atmosphere interactions. Um, and then this internal magnetic field gets distorted by the solar wind and what's coming from the Sun. Um, and so we often get um, on the sunward side of the magnetosphere this kind of blunted um compressed region, and then on the anti-sunward side a stretched elongated magnetotail, and this is um talked about as the night side of the magnetosphere versus the day side, and uh um, again at Earth like uh the processes and environment on the day side can be quite different than those on the night side of the magnetosphere. Um, it's really um, uh organized a lot by where the sun is relative to Earth rather than necessarily the latitude longitude you are at at Earth which is spinning underneath you. Um, and again that's somewhat different at different planets. Um, just for reference, here's low Earth orbit, geosynchronous orbit in a very crude, you know, grayscale. Um, anyone just to place the lunar orbit on here? Anyone know where it would be? Units of Earth radii or other. 60. Wonderful. So that is um, oops, upstream in the solar wind on the day side, but in the magnetotail on the night side. So you can get interesting kind of plasma variable plasma environments at the Moon because of this.
Okay, here's, you know, a cartoon of the magnetosphere, all the different component, well, not all, some of the different constituent components. Um, I'm always looking for better versions of this, so if anyone has a favorite um magnetosphere cartoon, pass it along, but this is looking from the side, on the sun is over on the left, North and South um poles of the earth, and then day side compressed and and night side elongated. Um, you start. Okay, so um, when I was looking up magnetospheric systems, I came across this paper um from a few years ago called The Joined-Up Magnetosphere. Does anyone know what this is a picture of? Yes, starling birds. Yes. Um, and uh, they kind of make these weird swarms. Um, and uh, this paper actually kind of compares this um system of starlings to the Earth's magnetosphere um as this kind of interconnected system of systems, um how a little movement over here can ripple through the whole thing and affect things over here, and these birds make these kind of crazy shapes and and morph, and I think it's for um, like uh to scare predators off, that they can like act like this large being even though they're made up of individual small little edible birds. Um, and then this paper also made a kind of nice comparison, or maybe a bit of a stretch, that um both these swarms of birds and uh our magnetospheric system can um disrupt power lines, and so I liked that that um these birds actually like sit on power lines, and just the sheer weight of that many birds can knock them down, compared to um geomagnetically induced currents at the magnetosphere um that can also knock out power grids. Um, so I liked this comparison as I was looking for kind of general um what is the magnetosphere, how does it behave? Um, because we're going to talk about all these little different regions that are named different things, but I think keeping in mind the big picture is um important throughout.
Okay, so starting at the very front, you know, what happens when the solar wind actually hits the magnetosphere? You get a, which is known as the bow shock. Um, this bow shock is different at different planets, uh looks different depending on both the solar wind driver and the obstacle it's impacting. Um, just like uh you can get different shaped shocks for different obstacles um here on Earth, and so what are some of the parameters that actually control this this shock shape? People want to jump in? Yeah. Yeah. Yeah, wonderful. So speed of solar wind. Yeah, definitely. Size of the planet or obstacle. Yeah. Yeah. Airplane. Yes. Yeah, wonderful. Density of the solar wind. Yeah, great. Yes. Yeah. Orientation of, well, for starters, whether there's a magnetic field that that the obstacle has, um, but then also how it's pointing. Yeah, wonderful. Oh, and the solar wind um magnetic field direction. Yeah, yes, great. Yeah. Yeah. Um, rotation of the planet obstacle for shock shape, I actually don't know if that would be a major player. Um, yeah, I I would think that might um come into play more in how the solar wind couples to the magnetosphere, what processes, but whether or not you have a bow shock might be more, you know, magnetic field strength at some distance. Yeah, if the magnetic field is very offset from the spin axis, then the rotation will change um change that shape pretty dramatically. Yeah. Okay, wonderful. Oh, one we didn't get to: so um, related to the assumption of whether the body has a has a magnetic field is whether it's um conducting or not. Um, than if it does have a magnetic field, uh Mach number of the solar winds, so all those properties, speed, density. Um, that last one also relates to kind of what the planet is emitting and and maybe uh most important if um it's not dominated by a a large magnetic field. Yeah, wonderful.
Okay, so once you get to the shock, um we get just behind that, closer to Earth, is the magnetosheath, and so that solar that shocked solar wind continues on towards the Earth, but it's denser, hotter, and slower after the shock. Um, and then as it flows around the obstacle, around the earth, it expands, cools, and speeds up again. Um, so Earth is not sitting in pristine uh solar wind. What's hitting the magnetosphere has been um through this shock, and has the properties have been changed. Um, and I thought this was a pretty cool visual um of the magnetosheath, uh whether or not it's totally accurate um yeah, debatable. Um, but I think it's a nice reminder that um one the solar wind properties are not what's hitting the Earth, they get um morphed and and changed, and then you can also have lots of kind of fine-scale or mesoscale structure within the magnetosheath that actually couples to the magnetosphere, um things like plasma jets and and bubbles and different um shapes that actually impinge on Earth's magnetosphere.
Okay, so then you actually get to the magnetosphere and its outer boundary, the magnetopause, um where this magnetopause is is determined by pressure balance, uh pressure in the solar wind versus pressure inside the magnetosphere, and at Earth we often make a lot of assumptions based on the various variables here and their values, and we can simplify this equation quite a bit and assume the dominant pressure in the solar wind is um this flow pressure, whereas the dominant pressure in the magnetosphere is magnetic pressure, and when you do this balance you come up with a um, you know, magnetopause distance at Earth around 10ish Earth radii, six to 12 maybe. Um, and of course, changes in the solar wind can change this quite a bit. Um, is this what we'd expect at other planets as well? Any ideas? I mean, the physics should hold, the top equation should be true, right, pressure balance? Um, but maybe. Yeah. Yes. So at Jupiter and Saturn, there's a a large internal plasma source from the moons, satellites, and so that creates more thermal pressure um uh within the planetary magnetosphere that we don't have here at Earth. Yeah, great. And I I imagine Fran is sitting back there that she will talk quite
A bit about this later in the week. Um, doing comparative magnetospheres, and uh, this is actually stolen from one of her tutorial slides a while ago. Um, but you see that that um the size of the magnetosphere at Jupiter and Saturn are inflated relative to just the magnetic field strength um and solar wind properties that you'd expect there based on this um internal plasma source from the the moons and satellites. Okay, so um like we spoke about Earth's uh magnetosphere is not empty. Um, it's full of charged particles, uh neutral particles, um ranging in energy from low to high that are all trapped um in the system by the the magnetic field.
Um, sources of this plasma um uh do we know where they come from? We heard earlier solar wind and ionosphere are the two primary sources at Earth um and the relative importance of these at Earth is is highly debated. It's kind of a a current question um as well as how the solar wind actually enters the magnetosphere and and create um contributes to this population. So while we know the general two sources, um when one is more important, when the other is more important, um how they fill the system are all open questions.
Um, does anyone know how we actually know this? Like how do we know where the particles are coming from in the magnetosphere? An electron sitting out in the plasma sheet is an electron; do it doesn't have like a a name tag where it came from. Um, does anyone know? Yes, so I heard particle species O+ and then also energy. Yes, um energy is a tricky one because once it gets into the system it can kind of be circulated throughout um you know that's what these little arrows are supposed to show that it's moving throughout the system and it can happen. Um, this circulation can happen on repeat, and so while the initial energy might be a good track or then later on if you're measuring it post-circulation, um other processes might have changed it. Um, composition is is one that is harder to change through the uh recirculation, and so um there are a number of uh papers by Lynn Kler um where she's used kind of ion composition measurements in the magnetosphere, and you can um attribute some of them to Earth's ionosphere, uh nitrogen for example or O+, whereas some um are are from the solar wind like helium double Plus or or higher ionization states of oxygen which um are hard to get in the ionosphere. And so um by tracking the the ratios of these different ion constituents over time and space you can kind of get an idea of where plasma has come from and how this changes throughout out geomagnetic storms or other other time periods, which I think is pretty cool.
Okay, again, um is this would we expect the same at other planets? Um, ionospheric source, solar wind source? Yeah, so internal other source, yep, moons. Um, is solar wind always a source? Yes, there should be less of a source depending on distance from the Sun and also how that coupling between solar wind and magnetosphere happens. And so um if there's uh easy access versus um more difficult access that should change as well. And since not to put Cran on the spot, but but has this been done at other planets of trying to track solar wind contribution to magnetospheric particles versus internal? Excellent, great, yeah. Okay, EXC.
Okay, so moving into these, once the plasma's in there, what does it look like? Um um at Earth you often hear about all these different plasma populations and different particle regions, um things like the plasma sheet, the plasmasphere, radiation belts, um some of the the main ones that get categorized are plasmasphere which is close to Earth, high density, very low energies, and this co-rotates with Earth and and primarily comes from the ionosphere; it's so low energy. Um, the ring current, kind of medium energies in the Kev energy range here at Earth, um uh creates a current around the earth based on ions drifting one way and electrons drifting the other, um and then at the highest energies the radiation belts; it's kind of MV type energy, so you're jumping up by orders of magnitude for each of these. Um, they occur in slightly different regions but kind of all overlap, which is why it's difficult to make um cartoons of them, um and also you know these categories are slightly artificial because um there's a fair amount of overlap between these energy ranges and regions that the particles occur at. So what's kind of upper level ring current versus lower level radiation belt are hundreds of Kev electrons; where do they fall? That's one that even within the radiation belt community sometimes people um consider them radiation belts and other times not, and and so I thought this was kind of a nice um uh again you know oversimplified cartoon of kind of where these different um uh particle populations land in terms of energy or temperature, but also density.
Um, the other thing this shows is that there's quite a wide range of both energies and densities that particles span within the magnetosphere, um making it very difficult to measure. And so if anyone works on instrumentation, often an instrument can only measure like a fixed range of of um uh let's say electron density or flux, and so to actually capture um this whole range of particle populations you often need lots of different instruments to cover little chunks of the energy spectrum. Um, and so this is just an example from the Van Allen probes mag ice instrument, um which actually was made up of three different instruments so that they could really capture the full dynamic range of expected um density of of electrons over this energy range, so from a observational perspective this makes things tricky, um and even trickier if you aren't just talking about the inner magnetosphere. So if you're something like um the MMS mission that measures um magnetosheath but also magnetosphere and magnetotail, the range of um different particle environments you fly through and have to try to capture is um quite broad.
Okay, so moving even further down, I didn't want to totally exclude the ionosphere. Um, as we move below radiation belts, ring current and Earth's plasmasphere, the source of the plasmasphere comes from the atmosphere and ionosphere, and um you often see these kinds of plots or pictures which show altitude on the y axis and then what we're seeing here in the middle is neutral gas temperature, so that's the atmosphere, the neutral gas, um and then electron density, the ionosphere, so the um ionized portion of the atmosphere, um and you can see there are different layers in the ionosphere, um the D region, the E region, the F region, um there are different regions of the atmosphere, thermosphere, mesosphere, stratosphere, and there's often um changes in temperature at these um boundaries, changes in temperature and density, um and what you can see is that there's variability in these profiles. And so um this, for example, I believe is solar minimum and solar maximum; you can see how this changes depending on solar driving. Um, I stole this from a previous um tutorial on the ionosphere because I thought it was nice to actually put ionosphere in at you know ionized and neutral particles on the same plot, um and you can see uh the ionosphere is actually a weakly ionized plasma that neutrals really dominate um at low altitudes in the few hundred kilometers and even further up, further up than I imagined, um and that these uh ion neutral collisions can really um uh strongly control the dynamics of this region. So the fact that you can't just assume everything is ionized makes things a lot more complicated, and part of the reason I like to at higher altitude.
Um, the other thing to point out as it relates to figuring out plasma sources in the magnetosphere is actually the composition of our atmosphere um and how this changes with altitude. And so N2 and O2 are really dominant here at Earth. Um, as you move up you get lighter um hydrogen, helium particles, um and then the rest of this I think you'll have a lot more mass based on uh Bob Marshall's slide, so we'll skip some of that, um but really just the composition of Earth's ionosphere and atmosphere, um uh and keep in mind at other planets this will be um potentially quite different. And then this is just to highlight the variability um that both uh the temperature profile and the density profile are highly solar cycle dependent, um and they're both inflated at solar maximum and uh smaller at solar minimum. And why I care about this, I'm sorry this is a little pixelly, but this um strongly affects how satellites fly through this region and um how uh atmospheric drag changes the orbit of a satellite in low earth orbit. And so I I have used um data from the SAMpex satellite here on the left, and the reason I liked this is um it was up for 20 years, so you actually get solar cycle variation and you can see that the altitude of the spacecraft um the slope of the change is um like noticeably different during solar maximum here near 2000 and then at the end of life in 2012 that um uh the decay in the orbital altitude is much steeper during solar max than solar min.
Okay, so let's pause again. Um, we've talked about this a teeny bit, but um because I uh like the magnetosphere and find the ionosphere complicated, messy, um I'd love you all to think uh specifically about Earth's magnetosphere and ionosphere and how they're connected and um how does the ionosphere affect the magnetosphere? How does the magnetosphere affect the ionosphere? Um, what are the processes that are important here, and why might um one person care about the other? So we'll just take two more more minutes, talk at your table, I'll walk around. Okay, let's regroup. Um, does anyone want to share some of these processes that came up? Yeah, this table, wonderful, we'll start here. Yes, um can you hear me? Yeah, yeah. Um, so I was talking to people in my table um I look at how they say reconnection for um enhanced convection in the magnetosphere or substorms, um and when I look at these phenomena I use magnetic indices that are measured by ground mag magnetometers, um but um here it's important to not to note that uh this enhanced convection in substorms actually give rise to currents in the ionosphere; currents then um cause magnetic disturbances which is what the magnetometers pick up. Yes, what I'm doing is literally just looking at magnetic phenomena using it's fully based on current systems. Yeah, wonderful. Yeah, there was I think same table and then oh, so I do aurora stuff, so I mean literally like if you're ignoring what the aurora is, I mean the aurora tells you what's going on in the magnetosphere a lot of times, so yeah. Yeah, wonderful. Um to this table, I won't I won't call on anyone. I guess I would just say that it's sort of it's the internal boundary for the magnetosphere, so whether or not the ionosphere is particularly conductive or not changes how say waves bounce, waves generated in the magnetosphere propagate and bounce back; it also changes how well how easily field lines can be dragged through the ionosphere, which again affects things like substorms. Yeah, yeah, so that ionospheric conductivity um controls a lot of magnetospheric dynamics, but also magnetospheric processes can control and mod um modify ionospheric conductivity, so it's really uh feedback there. Yeah, any other? Yeah, uh it's about ionospheric outflows and how they contributes to the reconnection rates in the day side as night side, so that's important where the ionospheric sprites contribute to the magnetospheric phenomena. Yeah, wonderful. So um how the ionosphere feeds plasma out into the magnetosphere, um how that plasma can then affect reconnection rates which we spoke about at this table a bit, um and then also there has been a lot of um recent interest in these ionospheric outflow and upflow processes and um where they put particles in the magnetosphere, only in the distant tail or can they directly place particles in the inner magnetosphere, so um a lot of open questions there too. Okay, anything we missed, major one? Yeah, yes, yeah, so um one way is that the ionosphere feeds Earth's plasmasphere, this kind of cold dense plasma in the inner magnetosphere. Um, during storm times the plasmasphere gets eroded and you get these um plasmaspheric plumes reaching out towards the day side that can actually reach all the way to the magnetopause, and so this um is a kind of relatively localized uh large large enhancement in the total density at at the reconnection site which can actually decrease reconnection rates, and there's been a lot of um uh modeling as well as observational attempts to see this um this effect in reconnection rates um based on uh co-plasma density. Yeah, yeah, excellent. Okay, the other one that sort of touched on with um aurora, but particle precipitation from the magnetosphere um can change the conductivity of the ionosphere, can create beautiful things to watch, um and uh can also change atmospheric chemistry even um high enough energy particles reach down into the atmosphere and and um ionized particles, so uh that's one of the more direct um connections in my research. Um, we'll skip this, this was a kind of maybe nice cartoon I found that shows all these processes, how they interact, how the different regions connect through different um uh yeah, I don't know if it helps clarify anything or just show how complex the system is, but thought I'd put it in here. Um, any other questions up till now, stuff we've talked about? Okay, if not uh did you have one? Oh yeah, yes, a little bit. Yeah, and how about yeah, O yes, so this um relates to all the different weird terms we use to describe slightly different particle populations in the magnetosphere, and so um I touched on the very main ones, was it here that you saw it or or earlier? Okay, okay. Um, there's the plasmasphere, cold dense, often there's um region just outside the plasmasphere that is just a teeny bit warmer but still cold, um sometimes more oxygen dominated, um as you move even further out there's a plasma sheet and then low plasma, and sometimes there's some layers in between there, the warm plasma cloak, I think is that layer just outside the plasmasphere that um uh is yeah a teeny bit warmer, sometimes a different composition and not always um not always present and not always um at all local times, so you can get kind of um slightly warmer plasma just beyond the cold dense region um that can affect what waves grow there, how waves interact with particles, just overall system dynamics. Yeah, but um it might be was it on that big list of different um yeah, yeah, you'll see it's just like right next to other ones, and so whether you pull it out or not is personal preference, often. Yeah, yes, yes, there absolutely is, and I actually um if if we had stuck with my older version of my slides that was included, but I looked at the time and the number of slides and decided to to remove it, but the cusp is very important, especially for kind of solar wind magnetosphere coupling, um as well as um so particles can come in through the cusp very easily because it's kind of a direct access point, they can also leave through the cusp, and so as a um source of of low altitude particles that make it out into the magnetosphere, the cusp is important on both of those. Um, there have been a lot of cool rocket missions that go through the cusp, measure these particle populations, and I think the Tracers mission, upcoming SMACK mission, um will fly through the cusp and kind of look at how reconnection on the day side changes the particles flowing in along the magnetic field into that cusp region. Yeah, yeah, yeah, I skipped a bunch, I skipped a ton. Yeah.
Okay, so um in the last bit we've been talking about kind of the static picture of the magnetosphere a lot. I thought I'd touch a teeny bit on the dynamics, um because this is system, the whole thing is is changing in time and space. Um, there's like we saw particle population spanning many orders of magnitude, and then we'll talk a little bit also um plasma waves spanning um full range of frequencies, and then the system is responding to changes in the driver, the solar wind, on time scales of seconds to years. And so you can look at the very short-term rapid changes in the system and also the kind of solar cycle ones. Yeah, um I think this is density, and so you can see the magnetosheath on the day side gets orange, gets denser than the solar wind, and then um in the magnetotail those lobes are often very low density, the kind of darker blue regions. Yeah, yes, I think this is sped up for um uh visual purposes, and so um actual time scale versus what we're watching it at um same as like auroral movies are often sped up. Um, this would be uh much much enhanced, so you can kind of see the solar wind, maybe you can see some magnetic field lines changing direction and and um a little bit as the driver, so that here is on less than second time scales, often solar wind changes in density, pressure and magnetic field direction we look at are kind of on on minutes or or larger scale; kind of a coronal mass ejection or high-speed stream would be long, you know tens of minutes. And so this is um sped up significantly, I don't know what time, you know hundred times maybe. Yeah, yeah, great question, so the flapping of the magnetotail, um while it can change rapidly, this is um obviously exaggerated.
Yeah. Okay, so some of these changes that drive this, um like we talked about, often in the solar wind, things like coronal mass ejections, um uh high-speed streams which I think other talks cover more, um can cause uh geomagnetic disturbances, and the two main ones we talk about are geomagnetic storms, these kind of global disturbances of the system that last days to to many days, um versus substorms which are um shorter, kind of more hour time scales and often more localized. And so some of the ways we measure these are ground-based magnetometers, and so for um geomagnetic storms the Dst index or SYM-H index is is um put together by magnetometers primarily around the equatorial region, so they really only pick up large scale global disturbances, whereas um auroral uh electrojet measurements of substorms are at high-latitude magnetometers that can respond to kind of um uh more localized dynamics in the in the tail region around the night side of the magnetosphere that might not be a a large scale disturbance.
One example of these time scales is the radiation belts. Um, so here we're looking at kind of a slice through the equatorial plane on the y axis; this um can be thought of as units of Earth radii away from the earth, um and color is the intensity or the the flux or density of these multi-energy electrons, and what you can see over this kind of few week period are three geomagnetic storms um at the bottom, and each one change um causes like a very dramatic change in the energetic particle population in the outer radiation belt on time scales of hours to days, um and sometimes it causes you know large enhancements like the last one, sometimes big depletions like the middle one. Um, so often we study changes in the magnetosphere on kind of um substorm, storm time scales, but um I do like to think about decades-long changes as well. And so this now is that same kind of you know distance from Earth on the y axis, and now over a 20-year period, and you can see the um change in the kind of net um content of the outer radiation belt over years and how it varies with solar cycle. And one thing to note is that um actually solar maximum is not necessarily when you have the most enhancement in the outer radiation belt; it's really the um declining phase of the solar cycle when you have a lot of high-speed streams in the solar wind that pump up the radiation belt content, um and the other thing that's kind of nice about this picture is you can see that this last um solar minimum or not last but the one here at the end um in uh around 2010 was a very deep minimum where the radiation belt was extremely quiet um and almost you know depleted for per year time scales. Yeah, this is based on SAMpex measurements, so like I showed again we have 20 years of SAMpex and then actually the last few years, so SAMpex re-entered in 2012 and um this is a a plot from Shin-in Lee; the last few years are stitched together with a CubeSat CubeSat measurements also from low earth orbit, so he kind of overlaid those to extend the measurement period. Yeah, so the question is you know why um at solar maximum is the radiation belt not most enhanced, and it could be there's less acceleration or more loss, and so loss through the magnetopause if if coronal mass ejections are really compressing the magnetosphere you might get a lot of loss out there. Um, I think studies that have looked at this have found that high-speed stream type storms tend to to cause a lot of
Acceleration because they last so long, the recovery phases um and that uh that acceleration tends to be what contributes to this kind of offset maximum. But the loss is probably—I think it's hard to measure—you you only have one measurement and you don't know what's actually um net loss versus acceleration.
Yeah, yeah. Yes, that's the Halloween storm. Yes, yes. And so you can actually see like individual storms on this that really um injected particles way down close to Earth um below the the outer radiation BT. Yeah. And I think if this extended um through this spring, you might see uh large our large May storm coming in also. Yeah. Um and also cool to overlay on this this is the DST index that's like smooth and averaged over month periods um but you can really see just how quiet that last minimum was um in aggregate and also how that radiation belt tracks um DST index, which is kind of cool.
Okay, so um we'll keep going. Uh so how the solar wind actually couples into the magnetosphere and drives geomagnetic activity, storms and substorms um is highly dependent on the orientation of the interplanetary magnetic field and whether it's northward, the same direction as Earth's magnetic field, or southward, oppositely oriented. Um and for southward you get um uh reconnection and and uh an open magnetosphere, so kind of more direct entry of solar wind into the magnetosphere versus the northward configuration that's a closed magnetosphere, at least in the cartoon version. Um although you can also get oppositely oriented um magnetic field over by the cusps um in this configuration. So it's it's uh somewhat oversimplified to say it's just closed or open; you might get reconnection happening, just not at the subsolar point.
Yeah, yeah, yeah. So um in the large scale picture, it's actually impressive that it it does um it is so closely related to um uh pristine solar IND IMF direction. But this is also why it's so difficult to predict whether you'll get a geomagnetic storm, the size of it, and the response of the magnetosphere just based on solar wind measurements because you don't know how that magnetic field changes once it moves through the sheath. And so, large scale picture, you can kind of often see after the fact, "Oh, we got a really big geomagnetic storm; um IMF bz was southward for a while, or it was northward, we didn't see much." But on the smaller scales um this is why it's so difficult.
Yeah, yeah, yeah, yeah. So you um right, it's not just always going to be southward for hours and then turn northward for hours. Um if it's rapidly fluctuating uh you'll get kind of turning on and off, and so you might get more um bursty reconnection. Um you might get uh if you look at the DST index, actually you know the classic picture of a geomagnetic storm is this big dip and then slow recovery, but actually you often see a lot of variability. Yeah, so the cartoon picture is is messed up by all these details and and reality very much so.
Yeah, yeah. Okay, so if you do have southward IMF um and reconnection on the day side, you get this Dungey cycle which um I have heard there are dances that depict it, but I am not going to do them. Um but you can kind of track the um magnetic field lines as they um move. And so here, blue is pure solar wind, red is pure, you know, both foot points in at Earth, and purple is once they've reconnected if one foot point is Earthbound and the other is in the solar wind. And so if you kind of step through these panels ABC, you start with um the two on the day side, you get reconnection, and then since the solar wind continues to flow about the Earth, it drags those foot points—there you go—drags those foot points back into the magneto tail where they can pile up in the tail and reconnect again. There you go.
Yes. Okay, okay. Um so my question to you is how fast is the solar wind? Roughly 400 km a second. What is the size of—how long does it take the solar wind to go one Earth radius or one Earth diameter? 6,400 kilometers for the radius, right, of the Earth. Okay, shout out when you got a number. Think in your head: is this two seconds, 20 seconds, 200 seconds, 2,000 seconds? 120. Okay, so then so that means one, two minutes. Two minutes to go a a radius or a diameter, which doesn't matter. Okay, how many—we're getting a lot of different different numbers thrown out here. So we're talking we're talking um couple of minutes to go a diameter. What was the size of that thing of your movie? How many like the magneto like where this is? So if you go upstream, it's 10 10 Earth radii, right? So that's five diameters. And so how many seconds to go from that's many? So reconnection minutes? 20 minutes? Yeah, it'll depend actually um how far down tail it actually has to go to cause this reconnection. And so there's um a fair amount of discussion of where that reconnection in the magneto tail is happening: is it near Earth or deep distant tail, or is it multiple places in the tail? So in order for to keep the Dungey cycle running, you've got to have this orientation for the whole cycle, right? So that means that your disturbance is upstream that generate this Dungey cycle have to remain persistent for tens of minutes, maybe even as much as an hour, right? Keep this in mind next Thursday when we start talking about other planets, particularly really big planets. Okay, just something to think about. We'll come back to this. Thank you for um interpretive dance.
Okay, so yeah, yes, where in the yes, where in the sounds good. Um where in the tail this reconnection is happening um is under debate, and one of the things the THEMIS mission has been trying to get at. Um the other thing to point out is, you know, this again is the cartoon picture looking side on; it's nice and clean; there's you know simple purple, red, blue, and they cleanly move from one to the other. Um global simulations—these are MHD simulations—now looking down at the equatorial plane with the sun over on the right hand side um and the color, the kind of pink blue color is the magnetic field um in the Z component, and you can see that it's not just like one clean reconnection point in the tail and then um uh things smooth beyond that, and within that there's all these weird little fingers happening and and um kind of scale structure that occurs in the tail and the the night side of the inner magnetosphere um that can make this this global picture um much more complicated.
Okay, and so if we just return to that cartoon picture again, if um solar wind is not southward, if we go to the northward picture, it's closed, but there can still be entry of solar wind into the magnetosphere and interaction between those two regions um primarily through Kelvin-Helmholtz um instability on the flanks. So this kind of solar wind streaming past the magnetosphere, you get an instability in these um vortices on the sides that can both um particles can directly enter through; they can also um set off all sorts of plasma waves um that can then uh change the system as well. Um and I was just uh I stuck this in here because I was just like looking at recent papers, and this came up in my inbox this morning that um uh this kind of um model of where you might get um this viscous interaction at Uranus, and they also do Neptune, and how that varies based on um solar wind um magnetic field strength, which you'll notice very small in both these cases um season whether the um uh so at these planets the spin axis is highly tilted relative to the sun-planet plane, and the magnetic field is also highly offset from the spin axis, so you have to um take into account both those angles uh when you consider this interaction. And so they had this nice model showing where you get um where you can get Kelvin-Helmholtz stability, where it is allowed in pink versus um where it is uh not allowed in black, and how that varies. I thought was cool. Cool.
Um okay, and then through these dynamics, we've talked a lot about particles, but um geomagnetic storms and substorms can also generate all sorts of different plasma waves, different types of waves occurring in different regions that can interact with different types of particles um energize cold plasma, accelerate hot plasma to become the radiation belts um scatter particles in pitch angle and cause them to enter its atmosphere and be lost from the system. So waves can really um uh connect different particle populations and um change the dynamics of the system quite dramatically. And again, this is the pretty cartoon that we see—every wave is you know in its neat little place—but when you actually look at the wave data itself, it's it's a mess; there's overlapping wiggles um electromagnetic static at all different frequencies um and so those who will be studying plasma waves um will have seen this in your data.
Okay, and lastly, we hadn't talked much about the aurora, but one of the ways we map these magnetospheric dynamics and one of the kind of visible um illustrations of substorm dynamics is through the aurora. And so um we'll skip this—oops—thought I'd highlight why I like the aurora. Did any of you see it in May during this last major sub um storm? This was a movie—I'll credit Long Xian, who's post-doc at Boston University but here in Boulder um and he just went into the foothills uh and took this video with his phone and a tripod um of the aurora over Boulder, which I thought was really awesome. Um and yeah, you can see all the kind of dynamics and and um kind of uh yeah, different colors, different—yeah, it's also amazing that his phone could do this.
Okay, the other reason I like aurora: it was one of the kind of early manifestations of magnetospheric dynamics. So there are these great old papers of like hand-drawn—someone staring up at the sky drawing little wiggles and curtains that they see and how they change throughout the course of a substorm and um trying to figure out what's going on in space from this um uh this kind of uh projection of it on on our um atmosphere, which is pretty cool. And then lastly, it's um a universal process, so we get aurora at different planets and and um it can tell us about the processes going on there um it can act as a map, so you actually know where the moons are mapping to in the ionosphere at Jupiter um and I suspect you'll hear more about this um as we go, but this is an example from Jupiter and then even Mars—the crustal magnetic fields that Mars can create um uh aurora there. And so you can get discrete aurora, which are the kind of pretty curtains that we see that you know most movies are showing, and then more diffuse kind of glow that um uh is generated by different processes, and you actually get both at Mars too, which I thought was um pretty interesting um um due to crustal magnetic fields, which we'll skip over a bit.
Okay, um any questions? Here, we're close to time, so I um we probably wrap it up here. I have a chunk more kind of comparative magnetospheres, but I think you'll talk about that um in a lot more detail later on, and I also have a chunk on space weather—kind of actual effects, why some of us care—but um maybe it's better to to just pause and see if people have any yeah, pressing questions or comments. Yeah, great question. So the kind of large yes um so what is a substorm? Hard to answer, but also how does it relate to that that Dungey cycle that we just saw? And is that Dungey cycle what's creating substorms, or is it something different? So that large-scale Dungey cycle that we saw of kind of the entire tail reconnecting and and um uh coming back in is typically geomagnetic storm related because you're getting this kind of global change in the system on daytime scales. Um substorms relate—if you go back to that more complex picture—maybe there's all sorts of um finer scale structure in the tail, so you can get reconnection happening um at different points in the tail across just narrow regions in the tail, not the entire magneto tail um and you can get that process generating um uh this same picture but on smaller scales, shorter time scales, and that is what I associate with substorm activity versus storms. Um does anyone have other definitions? It's a tricky question, and I think the substorm community is very um uh there is often a lot of debate within it um especially because it um was originated from an observational perspective of looking at the aurora, and so you actually don't know what's happening in the tail when you call something a substorm. Yeah, I've just heard of the different um schools of thought as like the outside-in versus the inside-out, so whether or not that reconnection takes place first in the tail, whether it takes place closer to Earth. Um yeah, yeah, yeah. So you've ever been to any kind of conference session on substorms—no one agrees. And there's also a big difference in in um what perspective people are coming from observationally: if they're they've been looking at aurora all their lives or um in situ measurements in the tail or doing global modeling.
Yeah, yeah. How's SEPs uh effects on outer radiation belt? Yeah, so solar energetic particles—yes—so direct very high energy particles from the Sun um can enter directly into the magnetosphere. Um SEPs can be both high energy protons or electrons, but typically slightly lower energy electrons, and so I primarily consider them as a um a source of high energy protons in the Earth's magnetosphere. And so um these high energy protons can actually directly populate the inner radiation belt, which is proton dominated um and so they can act as a source. Yeah, yeah, yeah, as a very direct source. Yeah, I um I've always been confused looking at cartoon pictures of the magnetosphere, but I wondered where the plasma sheet uh sources too within the magnetosphere. Um yeah, so it's just like this this um blob in the tail, right? It's um uh like where it comes on the inner edge or where it goes out extending to or either um I guess more so on the inner edge. Yeah, on the inner edge. So the plasma sheet in those pictures usually just ends when you get to the inner magnetosphere, and then there's a bunch of popu like radiation belt, ring current, plasmasphere. Um that plasma sheet—so particles in it in the tail, say 10 Earth radii out, are maybe keV energies, and as they move inwards they're um uh just adiabatically accelerated through um the magnetic field strength being stronger as they move inwards as they convect inwards. And so they can turn into the ring current as they um start to drift um around the Earth left or right. And so that's one place they go; they're kind of a source of ring current population um just energetically. Plasmasphere is too cold; radiation belts are usually a little too high energy, so um you need some kind of acceleration of the plasma sheet to get to the higher energies um but there have also been recent observations of um injections of particles from the plasma sheet that might directly feed the outer radiation belt, so be high enough energy to just kind of contribute to that. So there's a fair amount of overlap in these terms and and regions.
Yeah, yeah, yeah. It was more for like a magnetopause like distance—sometimes I've seen uh that the magnetic field is doubled at that distance, and I don't know if it was like what you thought about it or because like the two pressures like equalized, but sometimes I saw like 2D like together is squared instead of just B squared. I don't know uh in like the the equation that gets you the magnetopause or in observational—no, the basic equation. Um uh I I won't flip through all my slides to get back to it. Okay, okay. Excellent. Yeah. Um right, then I'll just say pass. Yeah, great question though. Thanks. Here in there. Yeah, I think um oh um I just a question about the influence of the interplanetary magnetic field on the magnetosphere. Um at least in simulations, we pretty much always neglect Bz, like a component facing along the direction between the Earth and the Sun. Um sorry uh I I wondered if you could talk about what the influence of a significant Bz component is—how that affects the configuration of the magnetosphere. Yeah, so in the coordinate system I typically use, Bz is along the yeah, along the Earth kind of north-south, but Bx is sun-Earth. I always talk about Bz, so yeah, Bx—yes—yeah. And so Bz is the one you always hear about, but obviously it's not just like a line that's tips only this way and this way; you get Bx and By components. Um By can cause a twisting, and Bx—Bx, By—people are kind of starting to pay attention to more because we can't explain everything with Bz, and it can it can um uh change that coupling; it can cause you know a shock to affect um maybe one hemisphere differently than the other or dawn-dusk asymmetries if you're in y. Um so those are very important to consider and usually totally ignored.
Yeah, yeah. So I'm not very familiar with Mars, but you showed an image of discrete aurora at Mars. Like, does it happen only where the crustal magnetic fields are? And I couldn't tell the difference from the those images you showed. So how do they determine that it's discrete and not diffuse? Yeah, so these images um uh maybe it's hard to see in the in the pink pictures, but there is um a teeny kind of more discrete line that you see versus just general glow, and it's even more obvious in the green um those uh like um uh more discrete lines that you see versus kind of general glow, and I believe—I'm not that familiar with Mars either—but um that the discrete is is uh tied to the crustal magnetic fields. Um did you want to add to this? Yeah, yeah. Wonderful. Yeah, thank you. Still pretty tied to crustal field locations. Yeah, yeah. Okay, cool. Um I see a two-minute warning, so I think let's wrap up. Um uh I'm gonna have to flip through like a bunch of slides, so just close your eyes for a second. Um any last questions while I'm flipping? Okay, okay. So I thought I'd end on a few of my personal takeaways. Um uh one is that you know because I study the radiation, we often um talk about the the application and kind of space weather applications, but I think there's both the applied perspective, especially studying kind of star-planet interactions as well as the interesting pure physics um and especially when you move into comparative heliosphere-magnetosphere systems um I think it's important to keep this in mind that you know studying our own magnetosphere can teach us about these other systems, and also these other systems can teach us um about whether we truly understand our own. And then the other you know takeaway is just the system is very complex and interconnected, and um that's both the beauty of it and the the challenge of it um and being able to compare these different planets or different stars is one way we can get a better handle on how things um interact with each other through this kind of turning it into a lab experiment—changing a variable and seeing what the downstream effects are. So um those are my two takeaways. Um I didn't bring—well—I was gonna pass around note cards, but we won't do that. I wanted you to just personally take a minute—we'll end with this—and kind of think about one of your takeaways from this, something you learned or found interesting, and then also a a question you had. Um if we have a minute, I'll go pass paper around; otherwise, just—oh, sure—uh I find it interesting to collect them personally; no need to put a name, or it's purely um for me to find interesting. So and also for you, I think um it's been shown that if you kind of pause after hearing a big spew of information and um think about it for a minute before moving on, you'll retain a teeny bit of it slightly better.