Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.astrosociety.org/abh/pdf/ABH11transcript.pdf Äàòà èçìåíåíèÿ: Fri Aug 26 02:01:39 2011 Äàòà èíäåêñèðîâàíèÿ: Mon Oct 1 23:13:51 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: ï ï ï ï ï ï ï ï ï ï ï ï ï ï

ASTRONOMY BEHIND THE HEADLINES A p o d c a s t fo r In fo r m a l S c ie n c e E d u c a to r s from the Astronomical Society of the Pacific www.astrosociety.org/abh

Episode 11: THE ACTIVE SUN with Dr. Phillip J. Erickson, MIT Haystack Observatory

Credits: Written, narrated and edited by Carolyn Collins Petersen Soundtrack production and original music: Mark C. Petersen Produced by Loch Ness Productions for ASP Special thanks to Dr. Philip J. Erickson ******** Begin transcript: HOST CAROLYN COLLINS PETERSEN: Welcome to Astronomy Behind the Headlines, a production of the Astronomical Society of the Pacific. On June 7th 2011, a monster outburst erupted from the Sun. It released a cloud of plasma that occupied a volume of space hundreds of times bigger than Earth. The blast ­ called a coronal mass ejection ­ emanated from an active sunspot region. If Earth had been in its path, that huge eruption could have had devastating effects on our power and communications systems, and on our satellites. Our planet dodged the danger, but the outburst was a reminder that we live with a variable star that can get pretty active from time to time. We are now headed into a time of increased solar activity. We asked Dr. Philip Erickson, an atmospheric researcher at MIT's Haystack Observatory in Massachusetts, to give us a scientist's eye view of our nearest star, and the influence it has on our planet ­ and our technology. He studies the effects of solar outbursts on Earth's magnetosphere and

Astronomy Behind the Headlines Episode 11: THE ACTIVE SUN

page 1 of 10 www.astrosociety.org/abh


upper atmosphere. He's also been featured in a series of Web-based videos called Space Weather FX, funded by NASA, and posted on the Haystack Observatory web site. Dr. Erickson, welcome to Astronomy Behind the Headlines. PHILIP J. ERICKSON: Hello to everybody. It's nice to be with you all. HOST: There's a lot going on with the Sun, so let's begin by talking about the Sun as solar researchers see it. We know there are a number of satellites observing the Sun such as Solar Dynamics Observatory and the STEREO mission. Tell us about some of the big discoveries coming from those missions. DR. ERICKSON: Yes, several of these satellites have in fact so much good solar science flowing out of them it's really driving a renaissance in the solar physics community in even further increasing their understanding of basic solar processes. For example, one of the more interesting things lately has to do with the engines that power solar storms. We know these engines occur, but until pretty recently it's been a little bit difficult to figure out exactly what triggers them. And, astronomers are still working to understanding the surface activity right at the solar photosphere and the chromosphere ­ these are the areas in the solar atmosphere; the photosphere for example, makes the visible light we see by ­ and there's a lot of activity in these layers, and also in the corona, the outer solar atmosphere. And astronomers are still working to understand what powers this activity. We've known for a long time that the Sun is really a magnetized fluid with a very, very strong magnetic field embedded in it. And that means that the magnetic field lines that thread through that fluid are not the dipole magnet that you remember from school with playing with iron filings. These are really dynamic, distorted, twisted field lines. Those magnetic field lines store energy. We've long suspected that high levels of activity in those same magnetic field areas are really what's the the engine or the power behind solar storms. The reason I'm bringing all that up is that you may have heard of a satellite called Solar Dynamics Observatory, or SDO, which is launched by the NASA Living with a Star program in the Heliophysics Division. This is a marvelous satellite with a number of
Astronomy Behind the Headlines Episode 11: THE ACTIVE SUN page 2 of 10 www.astrosociety.org/abh


images coming in, almost continually of the solar surface at eight to ten-second cadence ­ really unprecedented time resolution. One of the things it's been doing is looking very closely at those solar magnetic fields. Just a few weeks ago, it focused on something called a solar magnetic rope. Imagine that you've got a lot of magnetic field lines and they sort of get all bundled together into a ropy structure that conducts electricity. And, there's a suspicion that the rope was involved in triggering some of these solar storms. And this particular SDO study followed one of the ropes as it formed using this very high-resolution cadence provided by one of the imagers. And that was something that hadn't been possible before. And, as people had suspected but had not confirmed, the rope was in fact involved in heating the nearby area to 10 million degrees ­ a huge, huge temperature. Lots of energy storage, and at that point, the system sort of explosively reconfigured itself ­ the region ended up erupting in a solar storm. A lot of particles that used to be attached to that magnetic field line got thrown out, along with superheated gases, and those ended up forming a solar storm front. HOST: Could these magnetic ropes be behind the uptick in sunspots and coronal mass ejections and other activity that we see during each solar cycle? DR. ERICKSON: Well, the theory is that some of these ropes in fact are the driving engines that end up leading to these solar bursts. Understanding the way these ropes form, the way they get heated, they way they somewhat violently reconfigure themselves, is a real key to understanding how often, where, and how much material comes out of one of these coronal mass ejections or one of these solar storms. So yes, I think that it's going to provide important clues as to how the solar activity varies, how strong these events are, and what they end up meaning for the solar system. HOST: I recently read that the solar cycle after the one we're currently in could be a very quiet one? Why would that be? DR. ERICKSON: There's a group of scientists that have been using something called the Global Oscillation Network. That's a network of observing stations here on Earth. And what they're doing is they're studying surface pulsations ­ very minute motions on the surface of the Sun that are caused by really waves, in some cases acoustic waves, that are essentially rippling and echoing through the Sun's structure. One of the things
Astronomy Behind the Headlines Episode 11: THE ACTIVE SUN page 3 of 10 www.astrosociety.org/abh


they've found is that the wind flows that they're seeing on the surface of the Sun seem to reasonably well match sunspot formation for the solar cycle we're currently in. So the one we're going into, the oscillations seem to be in line with an uptick in solar activity. However, what they haven't found is a signature that they normally see that indicates when the NEXT cycle is going to start. That activity seems to be a little bit delayed or hasn't shown up yet. So, there's a suspicion ­ a growing suspicion that there might be fewer sunspots in THAT cycle, and perhaps maybe the Sun is going into another state that we haven't seen since we've been sort of paying attention to the Sun in detail, but it's hard to extrapolate. In any case, it's really interesting work because it's really peering INSIDE the Sun to see the roots of structures that end up existing in the Sun's corona and causing some of these solar outbursts. HOST: That tells us a lot about what's happening at the Sun. But, why should we care about solar activity here on Earth? DR. ERICKSON: Well, that's a good question. As it turns out, the Sun's activity really has a huge impact on the atmospheric envelope surrounding each planet that has an atmospheric envelope. HOST: What happens? DR. ERICKSON: Well, let's use Earth as an example. Earth has an atmosphere, and the material coming off of one of these solar outbursts is something we call the solar wind. This is the solar outer atmosphere continually boiling off material into the space between planets. When we have a solar outburst, we have an especially large change in the solar wind ­ a large pressure pulse, if you will. That pressure pulse has charged particles in it. In fact it has its own little magnetic field. When that pulse gets to Earth, it pushes on the charged and magnetized parts of our atmosphere. Essentially it's really pushing on the magnetic field that our planet emits out into space and that field has a tension, and the field in fact pushes back on the material that is in one of these solar wind bursts. The magnetosphere also flutters away in the solar wind similar to a windsock or the wake of a boat. And, when all that pushing and forcing happens and pushing back and forth, that ends up making the magnetic field lines move around in ways that lead to large changes in our upper atmosphere.
Astronomy Behind the Headlines Episode 11: THE ACTIVE SUN page 4 of 10 www.astrosociety.org/abh


HOST: Are you talking about aurorae ­ the northern and southern lights? DR. ERICKSON: Well, those are things that I would say are the most obvious effects, and may be the ones that have been noticed by humans for a long time ­ kind of the end products of space weather. And they're certainly beautiful and people have studied them for many, many years. They're really part of that larger phenomenon called space weather, which is a term that describes the general changes in our planet's environment, particularly in the lower, middle, and upper atmosphere that is caused by these solar outbursts. HOST: Does this solar activity have any other effects on our planet? DR. ERICKSON: Well, yes, it can actually play havoc with a lot of systems that are involved in our modern technology. A strong solar storm can disrupt satellite communications, and as you can imagine, that can affect everything from your cell phone to precision navigation systems such as the GPS cluster, in particular those things that steer precise landings for airplanes, and also inland waterways, for barges and other ships. If it's a strong enough solar storm, in fact, we can end up getting very large voltages on our power lines, which can shut down these power grids. If you (or someone you know) flies a high-altitude aircraft that happens to go across polar routes, or even if they work directly in the International Space Station, the Sun's activity has direct effects on health. That's one of the reasons why scientists will launch things like the SDO satellite, and the STEREO satellites, again looking at the sun from two different areas. And their goal is to study solar activity at the Sun in great detail. We're not just looking to understand that activity ­ we also want to ­ once we understand it ­ figure out ways to go the next step and predict a massive outburst so we can end up taking action to protect our technology. HOST: What can we expect during the next solar maximum? DR. ERICKSON: Well, in general, during an upswing in the solar cycle, the Sun should generate more and more sunspots, and solar flares, and coronal mass ejections
Astronomy Behind the Headlines Episode 11: THE ACTIVE SUN page 5 of 10 www.astrosociety.org/abh


throwing material our way as we head into the next maximum. However, I will tell you that the science of predicting exactly how strong a solar maximum will be, and when it will peak, is still very much a work in progress and certainly a hot topic for several people in the modeling and prediction fields. HOST: In Part II of The Active Sun, we discuss the effects that solar activity has on our technological society and the instruments scientists use to monitor solar activity and its effects on our atmosphere. ­ Part II ­ HOST: Welcome to Part II of our conversation about solar activity with Dr. Phil Erickson of MIT's Haystack Observatory. Dr. Erickson, let's continue our conversation with some thoughts about how solar activity messes with our technology. DR. ERICKSON: Actually, if you go all the way back to the invention of the telegraph in the mid 19th century, there have been effects on this technology and we slowly recognized that space weather can have very large consequences on the systems that our society really increasingly relies on for daily life. For example, the geomagnetic field when we get one of these solar outbursts has several resonances ­ it moves back and forth ­ and those resonances, if they get large enough, we call a geomagnetic storm. Those storms can cause things like the atmosphere to expand, which causes extra atmospheric drag on communications satellites, which shortens their lifetime. Radio communications from these satellites to and from ground stations have to pass through the upper atmosphere, and if you disturb the upper atmosphere, then the messages on these transmissions can get deflected and their information can get distorted, or in some cases completely lost. Another related effect is large disturbances in, say, trans-Atlantic cables carrying Internet traffic, since the Internet is so ubiquitous today, this makes a big difference. Another effect I can think of is GPS navigation units can end up getting a little bit of an error in their calculation of where you are. That can be a big problem if you are trying to steer an aircraft or a large ship during a big space weather event. And as I mentioned, aircraft traveling over the polar regions can be affected by communications blackouts.
Astronomy Behind the Headlines Episode 11: THE ACTIVE SUN page 6 of 10 www.astrosociety.org/abh


HOST: Those all sound pretty serious ­ and we'd definitely want to know about space weather effects in advance, so, what kind of early warning systems do we have? DR. ERICKSON: Well, there is one satellite called the Advanced Composition Explorer, or ACE that is actually sitting out between the Earth and the Sun. It's upstream from Earth by about usually 40 minutes to one-hour travel time. So a disturbance lifts off the Sun. A couple of days later, it has traveled the distance between the Sun and the Earth and we get maybe about a one-hour warning that this disturbance really is coming by. That monitoring satellite is very important and we certainly can use more ACE-like satellites to sit there and provide monitors. We now have the Solar Dynamics Observatory, and we have STEREO, which is looking at the Sun from two different sides. We also have the Solar Heliospheric Observatory, or SOHO, that's been there for quite a while. And some of these, when they spot disturbances, they will get a prompt effect. Images and data may be a few minutes later--that's the light-travel time from the Sun to the Earth. We're not exactly sampling the system that well though, so we can always use more monitors placed at strategic locations. HOST: There's also a very active community of researchers that also observes the Sun from Earth. Can you talk about them a little bit? DR. ERICKSON: Sure. I'm taking to you in fact from MIT Haystack Observatory, and this is a place where we've been actually monitoring the upper atmosphere from the ground for more than 50 years now, using a radar technique. A radar generally works as remote sensing tool. The analogy is, you know, you're in a darkened room, and you want to find out if there's a wall across the room from you, but you don't want to walk over and touch the wall so you have a flashlight in your hand. You click on the flashlight, and the light helps you remotely sense that there's a wall over there, even though you're not actually physically touching the wall.

Astronomy Behind the Headlines Episode 11: THE ACTIVE SUN

page 7 of 10 www.astrosociety.org/abh


So for us, in the case of radar for space weather monitoring, we need an illuminator, and our illuminator is a radio wave from a transmitter ­ a large antenna aimed upwards at the Earth's atmosphere. That radio wave in fact goes into the upper atmosphere and specifically, when it hits the charged part of the upper atmosphere, a small amount of that radio wave scatters off the charged electrons and ions in our atmosphere, which are made by solar extreme ultraviolet radiation every day. The very faint echo we get back ­ we can process that to contain an enormous amount of information about the physical state of the atmosphere: how dense that atmosphere is, by the strength of the return. We can tell, from the frequencies we get back, how hot hot or cold that atmosphere is, we can tell something about its composition ­ what kinds of ions and molecules is it made up of. We can even tell its line of sight speed ­ what speed it's moving at, toward us, away from us, horizontally. Now, the National Science Foundation has maintained a number of facilities across the western hemisphere­several arrayed across the Americas, up into Alaska, down into Peru, and they all use this powerful technique. We've been doing it as I mentioned from MIT for more than 50 years and we have a very long baseline that we can use to monitor space weather and its effects. HOST: And, of course, GPS technology is a valuable tool as well. DR. ERICKSON: That's right. The GPS system that you use say to navigate in your car, or if you're hiking with a GPS receiver ­ its primary purpose is of course to tell where you are. But, one of the things we can do is take the same data from those signals and in fact turn it around and employ it is a remote sensing space weather monitor. We apply essentially different applying different math and processing to the data we get and rather than finding out where we are, we end up finding out what the thickness is of the upper atmosphere that those signals that left the GPS satellites out at 20,000 kilometers ­ how those signals got delayed on their way to our receiver. And so, we end up figuring out the thickness or the number of electrons in sort of a line of sight through the charged upper atmosphere. Now the advantage is the Earth now has several thousand GPS receivers used for things like earthquake research. So we can take this same data and we end up getting a global map and a picture of the planet's
Astronomy Behind the Headlines Episode 11: THE ACTIVE SUN page 8 of 10 www.astrosociety.org/abh


response to solar outbursts. HOST: Now, that's on the professional side. Is there a role for the amateur community in observing the Sun and doing this kind of science? DR. ERICKSON: There is ­ of course as long as it's done safely. I definitely have to stress to your listeners that it is never safe to look directly at the Sun with your naked eyes, or ­ worse yet ­ into a telescope unless you have a proper solar filter that provides the proper attenuation or reduction in light. You can really cause significant eye damage to your retina and other parts of your eyes in a very short amount of time if you don't protect them by employing some of these measures. Now, having said that, there are ways that dedicated amateurs can, in fact, do useful solar observations in ways that are very safe. One I know of is through the American Association of Variable Star Observers. Some of those members in fact monitor disturbances in Earth's ionosphere, as we do, caused by the Sun. A lot of them in fact use homebuilt monitoring stations to do this in very clever designs and in very impressive ways. Other of these members will, for example, follow sunspots, document where they are, and document changes in their activity, which is another method that in fact has been used for centuries, for tracking the Sun's output and variations. HOST: What does the future hold for ways to predict solar outbursts? DR. ERICKSON: Well, as we've mentioned several times in this conversation, really we have a revolution in modern observational capabilities and I think these are, in fact, making a big difference in providing really the raw material which will improve our predictions. In addition, there's an instrument which not everybody thinks about, which is computational ability. There's been a real explosive growth in supercomputer and processing capabilities. These can be applied to the problems of modeling and predicting things in the Sun-Earth system and, in practice, what happens these days is that our models are beginning to do a better job at looking at both the big picture and all the little important details in the coupled Sun-Earth system. So, the technological community itself has also been raising space weather awareness in the general public ­ with podcasts like this one, for example ­ and also with those people in Washington who dictate policy
Astronomy Behind the Headlines Episode 11: THE ACTIVE SUN page 9 of 10 www.astrosociety.org/abh


and set budgets. I would also say that everyone knows even beyond these efforts, that we do still have a lot of work to do to improve and toughen up our navigation, electric and communication systems, but I think people are far more aware now of space weather effects than they were, and we're sort of gradually increasing that awareness. HOST: That sounds like a huge job. DR. ERICKSON: It is. There are indeed many joint projects between commercial, and government, and scientific groups. And these are trying to again push space weather, increase the awareness that it's actually there, and the idea is that all people are trying to push toward the common goal of really understanding the risks caused by extreme space conditions ­ and then to try to have society do what's necessary to protect our people and technology as a result. HOST: And at the same time, we're learning more about this star that we happen to live eight and a half light-minutes away from. DR. ERICKSON: Absolutely. Prediction comes after understanding. And so, one has to have a very basic physical understanding of the processes operating not only in the Sun, or on the Earth, but on the coupled Sun-Earth system, in order to be able to make a good prediction that's actually worthwhile. HOST: Well thank you, Dr. Erickson. It's really been interesting to get this deeper look into our active Sun. DR. ERICKSON: Oh, it's my pleasure and I would encourage your listeners to keep on paying attention to space weather ­ it's going to be an increasingly important topic as the next years come by. HOST: If you'd like to learn more about the active Sun and ways in which researchers are learning to understand its cycles, point your browser to www.astrosociety.org/abh. Thanks for listening!
Astronomy Behind the Headlines Episode 11: THE ACTIVE SUN page 10 of 10 www.astrosociety.org/abh