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).


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