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The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global AWESOME Network
The Day-Night Terminator
Prepared by Morris Cohen and Amanda AngellStanford University, Stanford, CA
IHY Workshop on Advancing VLF through the Global AWESOME
Network
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What is the Day-Night Terminator?
The day-night terminator is the line where the day side of the earth meets the night side. It is also called the solar terminator, or the twilight zone.
It marks an important transition from the daytime to the nighttime ionosphere.
The solar terminator has significance in many areas of VLF research: Causes variations in the Schumann Resonances Creates backscatter from transmitted VLF and Radio signalsHas potential application in earthquake detection
Source: www.nasa.gov
Day-Night Terminator
Source: http://time.gov/timezone.cgi?Eastern/d/-5/java
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How does the Ionosphere change at the terminator?
During the daytime, the sun’s rays are ionizing the plasma in the ionosphere, creating a denser, thicker ionosphere.
During the nighttime recombination occurs, making the ionospherethinner and less dense. Because of this the ionosphere begins at a higher altitude during the night than the day
Ionosphere
Ground
Day NightDay/Night
Terminator
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Sunrise/sunset times
http://aa.usno.navy.mil/data/docs/RS_OneYear.php
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Sunrise/sunset times
Full year times
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Twilights
6º below – civil twilight12º below – nautical twilight18º below – astronomical twilight
Horizon
6º below
12º below
18º below
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High altitude sunrise
Varying height of sunrise
h = RE(1-cosθ)cos θ
h
Civil twilight = sunset/rise at 34.7 km altitudeNautical twilight = sunset/rise at 136.2 km altitudeAstronomical twilight – sunset/rise at 296.5 km altitude
Sun sets at 85 km when sun is 9.43º below horizon
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Annual sun variations -- Sebha
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Annual sun variations -- HWU
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Annual sun variations -- NRK
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Diurnal variations
Day Night
Earth
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Diurnal variations at Sebha
0445 UT: Ionosphere showing typical nighttime variations
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Diurnal variations at Sebha
0515 UT: Sunrise terminator reaches Sebha
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Diurnal variations at Sebha
0545 UT: Sunrise terminator null effect in VLF data
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Diurnal variations at Sebha
0615 UT: Sunrise terminator second null begins
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Diurnal variations at Sebha
0645 UT: Sunrise terminator reaches transmitter
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Diurnal variations at Sebha
0715 UT: Ionosphere steady daytime signature
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Seasonal variations
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The Terminator and Earthquakes
Some studies have shown anomalies in the ionospheric day-night transition a few days before earthquakesStudies require further confirmation, large-scale examination
Source: T. Bleier, F. Freund, Earthquake Predictor. IEEE Spectrum, Dec. 2005. pp. 3-8.
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References
http://solar-center.stanford.edu/SID/educators/earthquakes.html
Melnikov A., Price C., Satori G., Fullekrug M. Influence of solar terminator passages on Schumann resonance parameters(2004) Journal of Atmospheric and Solar-Terrestrial Physics, 66 (13-14 SPEC. ISS.), pp. 1187-1194.
Predicting earthquakes, Granite batteries, Dec 14th 2005, SAN FRANCISCO, From The Economist print edition
T. Bleier, F. Freund, Earthquake Predictor. IEEE Spectrum, Dec. 2005. pp. 3-8.
F. Freund, Cracking the Code of Pre-Earthquake Signals, National Information Service for Earthquake Engineering,University of California, Berkeley (Found at: http://solar-center.stanford.edu/SID/educators/earthquakes.html)
Fraser-Smith, A., Introduction to the Space Environment: Electromagnetic Phenomena in the Lower Atmosphere
