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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Presentation transcript:

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

2 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: Day-Night Terminator Source:

3 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 DayNight Day/Night Terminator

4 Sunrise/sunset times 

5 Sunrise/sunset times  Full year times

6 Twilights  6º below – civil twilight  12º below – nautical twilight  18º below – astronomical twilight Horizon 6º below 12º below 18º below

7 High altitude sunrise Varying height of sunrise h = R E (1-cos  )cos  h  Civil twilight = sunset/rise at 34.7 km altitude  Nautical twilight = sunset/rise at km altitude  Astronomical twilight – sunset/rise at km altitude  Sun sets at 85 km when sun is 9.43º below horizon

8 Annual sun variations -- Sebha

9 Annual sun variations -- HWU

10 Annual sun variations -- NRK

11 Diurnal variations Day Night Earth

12 Diurnal variations at Sebha 0445 UT: Ionosphere showing typical nighttime variations

13 Diurnal variations at Sebha 0515 UT: Sunrise terminator reaches Sebha

14 Diurnal variations at Sebha 0545 UT: Sunrise terminator null effect in VLF data

15 Diurnal variations at Sebha 0615 UT: Sunrise terminator second null begins

16 Diurnal variations at Sebha 0645 UT: Sunrise terminator reaches transmitter

17 Diurnal variations at Sebha 0715 UT: Ionosphere steady daytime signature

18 Seasonal variations

19 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 pp. 3-8.

20 References   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  Predicting earthquakes, Granite batteries, Dec 14th 2005, SAN FRANCISCO, From The Economist print edition  T. Bleier, F. Freund, Earthquake Predictor. IEEE Spectrum, Dec pp  F. Freund, Cracking the Code of Pre-Earthquake Signals, National Information Service for Earthquake Engineering,University of California, Berkeley (Found at: the Code of Pre-Earthquake Signals  Fraser-Smith, A., Introduction to the Space Environment: Electromagnetic Phenomena in the Lower Atmosphere