Friday, April 21, 2006

April activity discussion

I would like to see some discussion of the activity this month, since there was some (first in several months.)
In the week of April 3, we saw some classic SID events (see http://www.spacenv.com/~rice/vlf/prv-nmlThru20060409.png), specifically 3 Apr 2130 UT, 5 Apr 1530 UT, and a real beauty on 6 Apr 2030 UT.
There were also some bursts that I'm very curious about: 8 Apr 2000 UT through 9 Apr 0200 UT, 14 Apr 2200-2330 UT, and 17 Apr 1700-2000 UT. There were significant auroral disturbances on 9 and 14 April, but nothing particular on 17 April (poke around in http://www.sec.noaa.gov/ftpmenu/plots/kp.html to see geomagnetic activity levels.) So did anyone else see these bursts, or are they some kind of local interference? Could they be
whistler or chorus emissions? Our operating frequency is rather high for that sort of thing,
but I believe they have been observed up to 40 kHz in some cases. Guess we need an
AWESOME receiver to sort that out.

Nick Gross's comments on quiet time activities are very good. One thing I would add is recording weather events, particularly thunderstorms. Thunderstorms can produce spikes
in the data and may have other effects, even at considerable distances.

Regarding radio propagation, VLF signals are a little tricky. The wavelengths are so long
(tens of kilometers) that they get into a sort of waveguide situation between the earth
and ionosphere. But basically you are correct, the conditions we see in the signal are due to
things going on between the receiver and the transmitter. Rather than simply being reflected
between the transmitter and receiver like shortwave signals, VLF signals can also be soaked up by the lower ionosphere during the day (D region absorption) and may be bounced around in complicated ways around sunrise and sunset. Does Stanford have any VLF ray-tracing (or waveguide mode) software they would care to share with the effort? The stuff I have is for HF and above. Comparing computer predictions with observations would be extremely interesting during quiet conditions.

One activity I would suggest for students interested in the behavior of radio waves at lower frequencies is to keep track of AM broadcast stations with an ordinary AM radio. During the day, you will only hear local stations due to D region absorption. As the sun sets, you will start to hear more distant stations, and after dark the AM band is jam-packed with stations, often talking on top of each other. In the morning you can follow sunrise, as stations in the east fade out before local dawn...then all of the distant stations go away around local sunrise. Here in Utah, I can hear stations from California to Ohio, Mexico to Canada at night. There are all sorts of strange fading and fluttering effects that illustrate various basic physics principles. The
main drawback with listening to AM stations is the content isn't very interesting, especially
at night (unless you are into Art Bell...) Anyway, if you compare the behavior of distant AM
stations to your VLF signal, you will see similarities and differences that are due to the behavior of the ionosphere at the different frequencies.

There is also a rather dramatic change in behavior between winter and summer seasons. I'm
seeing it in the VLF data this month. You can see very definite seasons in our various data sets.
A given day may not be very exciting, but if you collect data for several months, all sorts of
patterns and trends begin to pop out. See if you can figure out the plots on:
http://www.spacenv.com/secblo/BLO/cadi/RX/index.html
Why do the radio station signals have a sort of sine wave variation during the year? Can you
see effects of the Halloween 2003 geomagnetic storm in the 2003 data?

When we collect enough data I'll plot the VLF signal in the same format...should look cool,
though the Tuesday shutdowns are going to mess up the natural variations a bit...

Tuesday, April 18, 2006

SID Monitors and Solar Min, Why Now?

I was speaking with Richard Kurtz of South Side High School on Long Island. He has just set up his monitor and has a couple of students beginning some projects using it. He was concerned that it seems like a really boring time to put up a monitor because we appear to be at the very low point in the solar cycle with very little activity on the sun. In our discussion, though we came up with several things that could be done. In fact, solar minimum is the perfect time to start large scale testing of a new instrument, and what amounts to a new instrument network that will very soon become a global network. During solar minimum, with very few interesting events, we can get some base line data for how each instrument is supposed to behave.

<>There are several interesting issues that we need to explore regarding our monitors. One of the first things you should try to figure out is when does the particular station that you are looking at go down for maintenance. Each of the VLF stations, which are run by the government and used mainly for military traffic, goes off the air once a week or so for maintenance. It happens pretty regularly. If you take plots for say three weeks worth of data and past them up, you should see the maintenance period three times. Try to figure out which day of the week it is and post that on the blog so we can compare notes. (It looks like NML goes down on Tuesday Mornings.)

A second thing you should be able to do is identify sunrise and sunset. There is a characteristic drop in the signal strength at sunrise and a rise in the signal strength at sun set. Using the weather service or other reference (almanac?), you should be able to find your local sunrise/sunset times and see how it compares to your time. Notice that the student will have to convert everything to UT, which is another classroom activity you can do, especially in the lower grade levels.

<>Related to this is a more interesting issue. The effect measured by each monitor tells you about the state of the ionosphere at the point where the radio waves reflected. This means that a monitor in Boston tuned to a receiver in North Dakota is probing the ionosphere in the Midwest somewhere, assuming there is only one reflection. In that case, the sunrise effect will occur at sunrise at that point. Similarly, a monitor in California tuned to the same station is probing the ionosphere over Nevada, I think. This assumes that there is only one reflection. The question is can we verify that. I have a couple of thoughts on this matter but perhaps your students can come up with some ways to do this. Once you have an idea as to where the reflection is coming from, it should be simple geometry to get the reflection angle. This may be important to understand how the radio waves are interacting with the ionosphere.

Finally, you can begin to look at details of the data itself. There are some interesting daily features, and a good project would be to map some of these. For example, there is a hump right after sun rise. Does this change from day to day and season to season? Does it very by location? Similarly, different locations see a different shape during the day. Is this due to the location or due to the calibration of this instrument? I am sure there are other questions out there that need answering.

A research group at NCAR recently reported a predication that the next solar cycle was going to be 30% to 50% larger then was previously predicted. A news report on this is at http://www.csmonitor.com/2006/0309/p02s02-stss.html (If you can’t get this link, contact me and I will send you the report that I down loaded.). It is thought that this next cycle will begin in late 2007. By putting up your monitor now, working out these kinks and exploring the quiet period to know how each location responds. We will be ready when the real fun begins (just before the lights go out completely).

Monday, April 17, 2006

Hi There to the SID Monitor Community. Our Monitor in Cambridge MA (the Peoples Republic of Cambridge) has been up in an 8th grade classroom for a month now and we should be automatically uploading our data automatically soon.

I wrote up a "press release" for the school news letter and I think it will be going out to the local papers. I am including it here. It was reviewed by someone with newspaper editing experience and
Deborah Scherrer has looked at it. Feel free to copy it and adjust it to your local needs.

Best Regards
Nick Gross
Co-Director of Education for CISM
======================= Text Below this line=========

Peabody School Part of International
Space Environment Monitoring System

Students and parents entering the Cambridge’s Peabody Elementary School on Rindge Ave. from the rear may have notices an addition to the roof of the building. The addition is a Very Low Frequency (VLF) radio antenna that is connected to a specialized receiver located in Mr. Edward Rice’s 8th grade science classroom. This, along with the internet connected computer, make up a Sudden Ionosphere Disturbance (SID) Monitor. This device and others like it distributed around the country, and even around the world, are part of a science experiment to detect changes in the Earth’s upper atmosphere caused by activity on the sun.

The receivers were developed at Stanford University in Palo Alto, California and are partly supported by National Science Foundation (NSF) funds through the Center for Integrated Space Weather Modeling (CISM) in the Astronomy Department at Boston University. A Peabody parent, Nicholas Gross, is the co-Director for Education in CISM and provided the initial contact between the research program and the Peabody School. The radio receiver is provided by the project and the antenna was built here at Peabody.

The receiver is pre-tuned to the frequency of a VLF radio station run by the government in North Dakota. Radio waves at these frequencies reflect off the upper layer of the atmosphere back to Earth. In this way they can travel very long distances, even around the world. The strength of the reflection can change depending on the state of this topmost layer of the atmosphere, called the ionosphere. The ionosphere can be changed by activity on the Sun, such as solar flares, which will increase the density of charged particles in the upper atmosphere. This will change the strength of the radio signals received by the antenna on the Peabody School Roof. The strength of the signal is measured by the receiver and collected on a computer every 5 seconds. The data is regularly uploaded to the Solar Center at Stanford and placed in their database. It can then be compared with data from other receivers to see local, regional and even worldwide differences.

Students and teachers at Peabody can use the monitor and the Solar Center database to enhance their regular curriculum on the Sun and its effects on the Earth. It can also be used as the basis for impressive Science Fair Projects that are out of the ordinary. Mr. Rice noted that often students do not feel connected to the star in our backyard, only 93 million miles away. The monitor provides a tangible connection that the students have never before experienced before. Mr. Jay Mahoney, the 7th grade technology teacher, will also take advantage of the monitor to illustrate the use technology in exploring the world around us.

Though the Sun is currently quiet, it is expected to become more active starting next year as it goes through its 11-year solar cycle. Predictions for this next cycle suggest that the activity will be very high, providing many opportunities to ask interesting questions that can be answered by the data. The effects of this increased activity will also be apparent by increasing problems with radio communications, satellite malfunctions, power fluctuations, and increased danger of radiation exposure to astronauts.

The Peabody School is currently one of five schools in the database and the first school outside of California. Approximately 35 monitors have been shipped to various schools around the country and the program plans to place 100 of the monitors. The United Nations has designated next year as the International Heliophysical Year (IHY) (The heliosphere is the region that is influenced by the Suns magnetic field and the solar wind, well beyond the orbit of the planets.) The plan is to place a monitor in every country in the United Nations. In this way, students at Peabody will not only be connected to the Sun, but will be connected to other students around the world who are also studying the sun. In this way, the international connection of science can be experienced by students at the middle and high school level.



Tuesday, April 04, 2006

Monday SID

There was a nice little SID at about 2130 UT on 3 April in the NML data, corresponding
to a C-class x-ray flare. Maybe more activity on the way?