Date: April 21, 2010
Title: Sudden Ionospheric Disturbances
Podcaster: Jim Stratigos
Organization: Dogstar Observatory – www.dogstar-observatory.com
Description: Sudden ionospheric disturbances or SIDs are the result of high energy electrons or charged particles that slam into the earth’s ionosphere and temporarily disrupt low frequency radio signals. Solar flares, coronal mass ejections and even gamma ray bursts from objects billions of light years away can produce SIDs. With the increase in solar activity as the sun heads into a new sunspot cycle, solar flares and SID events will increase in strength and frequency allowing very simple amateur observatories to make meaningful observations. The simplicity of a SID receiving station makes it an excellent tool for educational outreach.
Bio: Jim Stratigos is an engineer, serial entrepreneur, part-time astronomy student and dedicated amateur astronomer. He is currently an industry consultant advising companies on telecommunications technologies. Following a 35 year career in satellite and wireless communications he has finally found time to pursue his true passions which include visual and radio astronomy and astrophotography. You can read more about Jim at www.dogstar-observatory.com.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Jim and dedicated to his wife Janie who puts up with his late nights at the telescope and his collection of astronomical gear.
Additional sponsorship for this episode of “365 Days of Astronomy” has been provided by Tom Foster.
Transcript:
Sudden Ionospheric Disturbances
Welcome to another 365 Days of Astronomy podcast. My name is Jim Stratigos and I am an amateur astronomer with an interest in visual and radio astronomy. My other hobby is ham radio and I get especially interested when I can combine my two passions and dive into the exciting world of radio astronomy. When you think of radio astronomy you usually think big dishes and racks of expensive and complex electronics. There is one area of radio astronomy however where inexpensive and often home made antennas and receivers can produce very exciting results. I am talking about the often overlooked area of very low frequency – abbreviated as VLF – radio astronomy where you can actually tune in to the sounds of the sun and even distant cosmic events. In VLF astronomy we will use the earth’s ionosphere as our antenna.
The ionosphere is the upper portion of the earth’s atmosphere that is constantly blasted by streams of particles from the sun which strip away the electrons from atoms in the atmosphere creating a plasma that is “ionized”. Ions are simply ordinary atoms of nitrogen and oxygen that have been stripped of some of their electrons. The ionosphere occupies an area roughly between about 60 and 1000 km above the Earth’s surface and is vitally important to long distance radio communications. The ionized plasma acts as a conducting surface that is capable of reflecting radio waves from transmitters on the Earth’s surface. Without the ionosphere there would be no shortwave communications and your local AM station would not fade out at night and get replaced by distant stations.
The ionosphere consists of several distinct layers known as the D, E and F regions with varying levels of ionization. During the day all three regions become ionized from the sun’s radiation and radio waves are reflected back to the earth at steep angles over relatively short paths. At night there is still ionization from cosmic rays but much weaker than in the daytime. The D region disappears at night and waves are reflected from the higher E and F regions resulting in reflections that occur at larger angles and thus longer distances. The nighttime ‘skip’ of distant radio signals is what makes distant shortwave stations louder at night and ham radio operators able to communicate over very great distances (hams call it “DX”) half way around the globe.
This change in propagation from low to high ionization levels makes the ionosphere act like a huge antenna to certain types of solar and cosmic events. Anything that drives a sudden increase in high energy photons or charged particles toward the earth can cause sudden changes in the ionization levels and can create what scientists call Sudden Ionospheric Disturbances or SIDs. SIDs can be created by solar flares which send streams of X-ray photons slamming into the Earth’s atmosphere. During times near the peak of the 11 year sunspot cycle, solar flares can be strong enough to disrupt radio communications, damage orbiting satellites and even disrupt power distribution and telephone communications.
SIDs can also be caused by gamma ray bursts (GRBs for short). GRBs are thought to be caused by supernova explosion in distant galaxies when a rapidly rotating star collapses into a neutron star or black hole. When the Earth lies in the path of the tightly beamed burst of energy, the atmosphere is slammed with massive does of radiation and a sudden increase in ionization occurs.
So how do we go about detecting SIDs? Can we simply tune to a distant AM station and listen? Well its almost that simple. Since the ionosphere reflects low frequency signals the best, we would prefer to listen for radio stations operating in the VLF frequency band below about 30 kHz. Fortunately there are some very high powered stations transmitting in this band for long range communications with submarines. Stations in the US and other countries transmit at power levels of several million watts into antennas that are tens of kilometers long. By using a VLF receiver tuned to one of these stations we can detect SIDs by looking for sudden changes in signal strength. We will see slow signal fades when the sun rises and sets but any abrupt change in ionization caused by flares or other phenomenon can be easily seen in the data. In its simplest form a SID receiver is very similar to a common AM radio but instead of a speaker they are connected to a PC so that signal levels can be monitored and recorded for later analysis. And even though the wavelength of VLF signals are many kilometers long, we can use simple wire loop antennas of only a meter or so in diameter to receive VLF signals. As an added bonus, VLF receivers can also detect other atmospheric events that are triggered by lightning strikes and aurora which can produce some very weird sounds known as ‘sferics’, ‘whistlers’ and ‘chorus’. Listen to some of the sounds you may hear on a VLF receiver:
(VLF sounds)
Research grade VLF receivers can cost over $10,000, but in the past few years several outstanding educational outreach projects based on VLF receivers have been launched to reduce the cost of SID receivers and utilize them as tools for educational outreach. The latest of these efforts is the SuperSID receiver developed in cooperation with the Stanford Solar Center and the Society of Amateur Radio Astronomers (see the show notes for links). I spoke to Deborah Schererr, founder of the Stanford Solar Center and project lead for the SuperSID program.
Jim: Deborah, thanks for speaking with us today. Why are SID receivers a good tool for educational outreach?
Deborah: Its hands on. And its personal. Its hands on and the kids don’t have to build the receiver but they do have to install it. They have to build there own antenna. That takes an hour or two. So there is a minimal buy in but there is a buy in. The second part is that the data they receive – one they can look at it – its in ASCII. You can literally look at the data and we provide simple graphing tools. The data is unique to their site and only their site. Their represents the ionosphere above their head and their data isn’t going to look like anybody else’s data. Its going to be special to them, to their location from the transmitter. So its very personal – its very intuitive for a high school student to understand and easy to buy into – easy to incorporate.
Jim: How did the Super SID design come about?
Deborah: Actually the original SID was designed by the AAVSO folks. So we hired a teacher who was an electronic engineer and said what we need is some little box like this that a high school student and high school teacher can use and they spent a couple of years coming up with something and came up with the first SID that we have. At the same time that was happening the EE people here at Stanford had a $30,000 instrument that was essentially studying the ionosphere and picking up the same signals at the SID box was. Now their instrument picked it up in much greater detail, higher sampling rate and more sensitivity and they were studying lightning disturbances in the ionosphere but NSF ended up funding both them and us to basically come up with a much cheaper version and put them all over the world. At that point it was only a $3,000 or $4,000 version, now its up to about $7,000 for the AWESOME receiver and they are still being distributed. We worked another year or two on the SID and we had to wait until the technology for computer sound cards was up to speed. Its now up to speed so we were able to replace a lot of electronics with the sampling from the sound card. An now we can produce these things for $50. The original SIDs were $200.
Jim: How many SID receivers have been produced?
We sent out of a total of over 400 SID and SuperSID receivers. The number of SuperSIDs is about 76 but we have only be distributing them for about six months or so.
Jim: How do you pick schools to receive SID receivers?
Deborah: A lot of it is word of mouth. I was involved in the International Heliophysical Year and we were distributing these receivers for that. What I did was work through the education representatives for the various countries and I also worked through my own network and also worked through the groups that were hosting IHY meetings. We happened to have a lot of instruments in Africa because we got interested in working with scientists in Africa to improve their research situation. One of the ways you improve the research situation is by improving the resources that kids in high schools and middle schools have. We worked through the IHY to place instruments there.
Jim: Have the SID receivers made an impact on students?
Deborah: Abolutley. We had a lot of high school kids do research projects. One of them (Leandra Merola) took on a SID project in her senior year of high school. Did the SID project, turned it into several competitions, won high awards with it and used it as part of her ability to get into a very exclusive private school; decided she wanted to major in physics because of this experience and she now is a senior and has a job in Colorado working on similar science.
Jim: Will students be able to make real contributions to science?
Deborah: Its very possible. There are some hints that some of these signals could serve as precursors to earthquakes and there are people looking at that. Its conceivable that kids could come up with data to either support or not support that hypothesis. As you know, the solar cycle has been very, very weak for the past three years. So we have had fewer kids interested in working with solar data because there isn’t much solar data. They have started to look at sunrise and sunset terminator effects and other ionosphere effects. There are things that these instruments will pick up that we literally don’t know what causes them. The AWESOME monitors were picking up terrestrial gamma ray flashes which were only discovered four or five years ago. Now there is a whole research project looking at what causes gamma ray flashes that are in our own atmosphere in the ionosphere. They know they are related to lightning but they don’t know exactly the mechanism that triggers them. These are things our SIDs students could pick up as well.
Jim: Can the SIDs data be correlated with data from satellites like GOES?
Deborah: Absolutely. The GOES satellites look at the Earth but they also look at the Sun. What the GOES satellites do is track solar flares as the emanate from the Sun. The students then track the same flare’s effect on the Earth’s ionosphere. If you look at the graphs; sort of an instantaneous build up and then slow build down are very similar in shape. So the kids will detect the ionospheric change caused by a flare and then go look at the satellite data which detected the actual solar flare and then compare those. From the satellite data they can even trace back the flare to the sunspot or active region on the sun that produced the flare.
Jim: Will interest in SID pick up with the new solar cycle?
Deborah: Yes. Before the end of the last solar cycle we were picking up three or four flares a day and we have only picked up three flares in the last three years since we were in the minimum of the cycle. It is starting to ramp up and this is a really good time for the kids to get their instruments out.
I have been speaking with Deborah Schererr project lead for the SuperSID program.
So why not go out and build your on SID observatory? In addition to the SuperSID receiver, there are a number of other simple VLF receivers that can be purchased assembled or as a kit. You can find links to sources for SID receivers in the show notes.
Thanks for listening.
End of podcast:
365 Days of Astronomy
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