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Dr. Vassilis Angelopoulos is an Associate Professor of Space Physics at the Earth and Space Sciences Department at UCLA, a member of the Institute of Geophysics and Planetary Physics, and the Principal Investigator of the THEMIS mission. His current research tries to understand how particles are accelerated in Earth's magnetosphere, how the upper atmosphere and ionosphere respond to space currents, and how the lunar environment is affected by its interaction with the solar wind. He is currently working on storms and substorms at Earth and on the development of a new mission, called ARTEMIS, to study the lunar environment with two satellites. |
On July 22, 2008, Vassilis Angelopoulos answered selected viewer questions about the THEMIS mission, for which he is Principal Investigator, as well as general questions about the aurora and magnetosphere. Please note we are no longer accepting questions, but see Northern Lights and our Links & Books section for more information. Q: On July 24, 2008, the Web site of the journal Science published an article by you and 16 coauthors describing an exciting discovery from the THEMIS mission about what triggers auroras. Can you explain the finding briefly for our readers? Thanks, and good luck with the rest of the mission. A: On February 26, 2008, the five THEMIS satellites were on a major conjunction, lined up parallel to the sun-Earth line and waiting for a substorm to take place. A substorm did happen and was captured on all satellites and by the THEMIS ground imagers. Each satellite saw the expected signatures of currents and flows, but careful timing of those signatures revealed the sequence of events that THEMIS was designed to measure, pinpointing the origin of substorms in space. In the July 24th Science Express issue, the team reported that the process of magnetic reconnection was observed at 20 Earth Radii away (130,000km) at least 1.5 min before auroral intensification, and at least 2 min before near-Earth current disruption, and about 3 min before substorm expansion. These results demonstrated that substorms are likely initiated by tail reconnection. The results were confirmed during two more substorm events. Further analysis of events from the second year of THEMIS operations will determine the generality of these findings and their dependence on solar wind conditions. Q: Considering that our sun and the billions of stars all are gaseous furnaces, and they emit gases that cause the aurora of Planet Earth, might not such emissions over eons of time be related to the dark matter that is in the universe? As a layman, I think that the universe must be thoroughly polluted! Your views, please. Thanks! A: As tenuous as solar wind may be, it is still considered classical, measurable interplanetary and intergalactic matter. Also, the amount of gas emitted from the sun is tiny compared to the solar mass itself: Less than a thousandth of the solar mass will be lost in the sun's lifetime this way. Such material cannot make up for the deficiency in matter in the universe—70% of the mass of the universe is unexplainable and is considered to be in dark matter state. Q: With the way technology is going, do you think we will ever know the forecast of the aurora borealis ahead of time like we do with weather? A: Yes. We are finally beginning to make sense of it all. THEMIS is expected to provide the first accurate data to address the question of how the aurora is driven from space and how it intensifies. This knowledge will be integrated in models and preliminary predictions will be tested against data to improve the models. This cycle is how 50 years ago we learned how to forecast atmospheric weather. Q: The first entry of the NOVA scienceNOW Web feature on the northern lights shows a lovely colored aurora. But the only time I ever saw the aurora—and believe me, it surprised the heck out of me—was one night driving up the Maine Turnpike about 10 years ago, and it was all white. (It was also beautiful, rippling away like a giant sheet in the sky.) Does the aurora lose its color the further south it's seen? How far south can one see the aurora? Thanks very much, and good luck with your mission. A: The auroral color depends on the energy of the electrons that create it. The more energetic electrons scatter off of more atoms or molecules, and so they penetrate deeper into the ionosphere. (Think of an electron as a billiard ball that is shot through a hangar with bowling balls hung from the ceiling representing the heavier atoms and molecules. The billiard ball will slow down only a bit with every grazing collision with a bowling ball until it eventually slows down completely. The faster the billiard ball, the further it will manage to get through the volume of bowling balls.) Different altitudes have different concentrations of nitrogen and oxygen, resulting in the different colors. Very energetic electrons will generate a mixture of blue and red colors at lower altitude (80-100 kilometers), which appears pink, and also excite red and green at higher altitudes. Seen from directly below you will see a blend of colors, closer to white. It is rare that you see the aurora in Maine, because that happens during intense storms, which carry strong currents. That's when the electrons are most energetic, and the aurora gets to lower altitudes and appears closer to white. Q: Solar storms of about 500 or plus nanotesla will penetrate Earth's magnetosphere and cause huge disasters in powerhouses around the world. Not only this, but satellites and telecommunication will also be affected by it. By the time SOHO, ACE, and others inform us about it, we will have about 90 to 150 minutes to react. Solutions like BLACKOUT are hard to be carried out. So, regarding this, what are the preparations and other solutions to it at the international level? A: SOHO images the solar corona and gives us 24-hour warning, but our models are not high enough fidelity to predict what will hit Earth. ACE measures the solar wind directly upstream of Earth with about 2 hr advance warning, but our models are not sophisticated enough and fast enough yet to predict effects. But with the launch of STEREO, THEMIS, and soon the Solar Dynamics Observatory, we will make significant advances in our understanding of both those regions, and with the new data the models will become more advanced. I suspect that by the next solar cycle, available model fidelity and speed could reach operational capability. Q: I would love to see the aurora borealis within the next few years, perhaps by the time I reach my 70th birthday. Did I understand that 2011-2012 might offer the best opportunity? Where would be best to view then? A: If you really want to watch large storms, you can get a 1- to 2-day advance warning by following the online NOAA predictions, derived from solar imaging. If you want to watch any active aurora per se, which can be just as dramatic locally during substorms, then a mid-March or a mid-September trip to Alaska should do it, any year. Auroral dispays tend to peak in those periods. Q: Thanks for taking the time to answer our questions. I am the maintainer of the free real-time operating system RTEMS used on this mission. I am sure that the program is using other free software like GNU/Linux. Could you share how the use of free and open-source software has impacted the space research community? Thanks. A: Academic institutions like mine, in the pursuit of knowledge and understanding of Earth and space, thrive on exchange of ideas, results, and research tools. We benefit tremendously from open-source software and incorporate useful tools quickly in our program. THEMIS has benefited significantly from programs like yours, both on the mission operations and on the science analysis. Thank you for sharing this view and for your continued efforts and support. Q: When I was a young child, my parents woke us up during the night to go outside to see the northern lights. I remember it, but I don't remember how old I was. It must have been in the early-to-mid 1950s. I lived in Quanah, Texas, which is located at roughly 34°N, 99°W. Is there a time recorded during the 1950s when the northern lights could be seen that far south? Thanks. A: Large storms peak in intensity during the declining phase of the solar cycle. There were two very large storms that took place on September 13, 1957 and February 11, 1958. They were at the peak and start of declining phase of solar cycle 19, one of the largest cycles recorded. Q: Can you explain how the energy from the solar wind gets stored in the Earth's magnetic field and then released so quickly? I believe it involves something called "magnetic reconnection," but I'm hazy on the details. Thanks. A: Magnetic reconnection is a process during which oppositely directed field lines pushed against each other snap and connect into U-shaped pairs. This happens at the dayside, where the solar wind magnetic field pushes against Earth's field. Each U-shaped field line which reconnected has one end tied to the Earth and the other end in the solar wind. You can imagine the field lines like strings connecting the interplanetary space to the polar ionosphere. As the solar wind passes by Earth, the reconnected field lines get dragged towards the nightside and are then stretched. With time, more and more of those strings pile up at the nightside, and the magnetic fields there become very strong. The magnetic field contains magnetic energy, like the energy stored inside the core of a solenoid magnet when you crank up the current passing through the wire. This way mechanical energy from the solar wind is stored as magnetic energy. At some point something "gives" and this energy is released into kinetic energy inside Earth's environment. This starts to happen in a matter of minutes, if not seconds. THEMIS is designed to discover where this happens and so focus the scientific community's attention to the right region of space and the correct physical process. Q: What causes the northern lights? I mean, I know it has to do with the sun and the Earth's magnetic field, but not in depth, and I was wondering if you could tell me. A: The auroral light is primarily caused by electrons that are streaming with high speeds from near-Earth space. (See previous answers regarding auroral light color for more details.) The electrons are accelerated to high speeds mostly by electrostatic potentials, driven by space currents. This is similar to your home electricity causing electrons in your fluorescent tube to hit the gas in the tube, causing it to glow. The origin of the space currents is still under investigation. Q: What's the single most exciting thing you can imagine coming out of your THEMIS mission? Thanks! A: We designed THEMIS to discover the trigger of substorms. But as it goes with most science investigations, surprises from serendipitous discoveries may surpass the stated goal of the mission. Q: What is the average cycle of aurora activity? Also, are there any photo records of the Great Aurora of February 10-11, 1958 ? How can I see them? A: The typical recurrence rate of the auroral brightenings is 3-4 hours, the same as that of substorms. I am not aware of any images from the February 11, 1958 aurora, but it may be possible to find them in newspapers from that time. Q: I am a ham operator, KA1RQN. The death spike shot up 10' instantly. I would like to make 2-meter antennas for emergency use. How did it shoot up so fast, and what was used to make the antenna? Thanks. A: The death spike is a tube, which is made up of a wound-up strip, 0.1mm thick x 127mm wide x several meters long, made out of Elgiloy. It is formed in a helical fashion, such that it tends to unwind to reach its zero energy state. When wound up into a 127mm long canister, about 50mm in diameter. Deployment is self-powered but restowing into the canister takes skill and can be dangerous. Q: Do the northern/southern lights emit their "secondary" waves in a range that runs largely outside the human eye's capacity to see? Or do they consist of mainly visible light? A: The aurora emits also outside the visible range, but in the ultraviolet that gets absorbed by the atmosphere before it reaches us on the ground, whereas in the infrared we just don't see it. Q: Since the aurora results from material given off by the sun, is the display more prominent in the summer or in the winter? A: Though there is aurora due to the direct interaction of the solar wind with Earth (called dayside aurora), the most intense aurora is due to the release of solar wind energy after it has entered the Earth's environment as magnetic energy at the nightside. The release of that magnetic energy is the cause of the intense nightside aurora; this is why the aurora is most intense at the nightside. The aurora varies with the solar wind energy coupling to Earth. This peaks near the equinoxes (around a month centered in March 21 and September 21) because of the preferential direction of the solar wind magnetic field (that is arranged into a giant spiral around the sun) relative to Earth's magnetic field.
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© | Created July 2008 |
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