The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford,...

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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

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Page 1: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

The Day-Night Terminator

Prepared by Morris Cohen and Amanda AngellStanford University, Stanford, CA

IHY Workshop on Advancing VLF through the Global AWESOME

Network

Page 2: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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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 signals Has potential application in earthquake detection

Source: www.nasa.gov

Day-Night Terminator

Source: http://time.gov/timezone.cgi?Eastern/d/-5/java

Page 3: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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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 ionosphere thinner 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

Page 5: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Sunrise/sunset times

Full year times

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Twilights

6º below – civil twilight 12º below – nautical twilight 18º below – astronomical twilight

Horizon

6º below

12º below

18º below

Page 7: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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High altitude sunrise

Varying height of sunrise

h = RE(1-cos)cos

h

Civil twilight = sunset/rise at 34.7 km altitude Nautical twilight = sunset/rise at 136.2 km altitude Astronomical twilight – sunset/rise at 296.5 km altitude

Sun sets at 85 km when sun is 9.43º below horizon

Page 8: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Annual sun variations -- Sebha

Page 9: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Annual sun variations -- HWU

Page 10: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Annual sun variations -- NRK

Page 11: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Diurnal variations

Day Night

Earth

Page 12: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Diurnal variations at Sebha

0445 UT: Ionosphere showing typical nighttime variations

Page 13: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Diurnal variations at Sebha

0515 UT: Sunrise terminator reaches Sebha

Page 14: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Diurnal variations at Sebha

0545 UT: Sunrise terminator null effect in VLF data

Page 15: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Diurnal variations at Sebha

0615 UT: Sunrise terminator second null begins

Page 16: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Diurnal variations at Sebha

0645 UT: Sunrise terminator reaches transmitter

Page 17: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Diurnal variations at Sebha

0715 UT: Ionosphere steady daytime signature

Page 18: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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Seasonal variations

Page 19: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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The Terminator and Earthquakes

Some studies have shown anomalies in the ionospheric day-night transition a few days before earthquakes

Studies require further confirmation, large-scale examination

Source: T. Bleier, F. Freund, Earthquake Predictor. IEEE Spectrum, Dec. 2005. pp. 3-8.

Page 20: The Day-Night Terminator Prepared by Morris Cohen and Amanda Angell Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global.

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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


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