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Sunrise/Sunset-related Phenomena


During periods of low solar activity (e.g. 2006) it may be necessary to focus on aspects of the data other than solar flares. Your students might be able to do something related to the sunrise and sunset "signatures" that the monitors pick up. Your students may have wondered where, between the transmitter and the receiver, is the sunrise or sunset being sensed. In other words, if your monitor is 3000 miles away in longitude from the transmitter, where is the "sunrise" occuring that is being picked up? Is it local, or at the transmitter, or in between, at the point where sunlight hits the ionosphere, or an integrated representation of the sunrise moving across the distance? Or??? Can your students find out?

We have generated step-by-step instructions for answering these questions. See Sunrise, Sunset Activity. You can use this activity to introduce your students to their SID data and the concepts relating to it. We also hve some background info about the ionosphere that you students might find helpful.

When directing your students to explore these sunrise and sunset phenomena, make sure that they fully understand that sunrise and sunset fall at different times every day and why. Do they understand where the Sun sets at the solstices and equinoxes and in between? Do they understand the concept of timezones, longitude, and latitude? On the activity, your students will plot the sunrise and sunset times from your SID monitor, at their local site, and at the transmitter. If they wish, they can plot this information for different sites and different transmitters by accessing the SID database at http://solar-center.stanford.edu/SID/data/.

You may also wish to encourage your students to delve further into this research. Why are the shapes of the sunrise and sunset signatures so strange? Are they are consistent across monitors and/or sites? Do the shapes change with longitude, with latitude? Do the shapes change with season? Could weather or thunderstorms be influencing the shape of the signature?

Does the length, i.e. extent of time of the signature, change during the year? At your site? At others? Does the length change with different monitors, with different latitudes, with different longitudes, with different seasons? Does the sunset signature differ when there has been solar activity that day?

The sunrise and sunset signatures have dips and rises that correspond to different ionization events. How long before actual sunrise is the first dip? What could be causing that? Are the sunrise and sunset signatures similar? If not, why not? What about for other monitors at other sites?

Once you gather data and think you have discerned some answers, see if you can predict the sunrise and/or sunset effects for your monitor, for a distant SID monitor, and for a monitor that is tracking a different frequency. The ability to accurately predict events is a good test of whether your discoveries ("theories") are correct or not.

There is some intriguing research about whether large earthquakes are associated with ionospheric changes. In the laboratory, the crushing of rock crystalline structures generates electromagnetic fields. The theory is that similar events in the Earth can affect the ionosphere and thus show up as precursors to large earthquakes. This research is still controversial and, if there are effects, they may be too subtle for the SID instruments to pick up. However, at least one research group claims to have found unusual sunset signatures associated with the devastating earthquake and tsunami of December 2004. The paper is: Unusual Sunset Terminator behavior of VLF signals at 17kHz during the Earthquake episode of Dec., 2004. One would think that, for a monitor to pick up these changes, the epicenter of a large quake would need to fall on or near the line between the transmitter and receiver. However, these researchers and the transmitter were in India, a good ways from the epicenter. They found the sunset signature was shifted later by 9 minutes, a significant change. If your students do pursue something of this nature, make sure you make it clear to them that this is very new and tentative research, that their SID or AWESOME monitor may not be sensitive enough to pick up the changes, and that they may or may not find any good results.


If your students are able to answer any of these questions, please let us know and we will highlight their research on the website!

©2008 by Stanford SOLAR Center