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Solar Eclipse 2018 Ionospheric Changes Detected with
an INSPIRE receiver
D. Gallagher, NASA/MSFC
https://ntrs.nasa.gov/search.jsp?R=20180001509 2020-07-13T01:49:37+00:00Z
First Let’s Talk About Radio Waves: Natural and Manmade
Where they go depends on our ionosphere
• The ionosphere is at the top of our atmosphere • ~90 km to 1000 km in altitude • Made of atmospheric gas ionized by solar UV
Natural
Manmade
Radio Noise from Lightning
Lightning produces a broad spectrum of radio waves. Most of the wave energy is usually confined between Earth’s surface and the ionosphere.
• Spherics is the crashing sound you may have heard while listening to AM radio.
• Tweeks sounds a little like a plucked string and can come from anywhere in the world, traveling between the ground and ionosphere.
• Whistlers have been in space, nearly following magnetic field lines in the ionized gas of Earth’s magnetic environment.
Radio Noise from Lightning
• Sometimes lightning wave energy goes through the ionosphere.
• The low frequency part is guided by the magnetic field.
• Where somewhat higher frequencies move faster than lower frequencies.
7.52 sec
Frequency
0 Hz
Time 0 sec
5.5k Hz
So What is to Be Done with VLF Waves? Answer the question: “Does the eclipse shadow change the ionosphere enough to cause VLF waves to behave like they do at dawn/dusk on normal days or will VLF radio noise be like it is at mid-day without an eclipse?”
Dawn/Dusk
Mid-Day
What are VLF waves like at these times without an
eclipse?
Mid-Day Eclipse What are VLF
waves like during this
eclipse?
Do what with the answer? Publish in the INSPIRE Journal! Other VLF enthusiasts may also submit their observations from elsewhere along the path of totality that can be used to answer the question.
2017 Solar Eclipse VLF Site
Between bean fields near Guthrie, KY
2017 Solar Eclipse VLF Site
Between bean fields near Guthrie, KY Photograph curtesy of Jesse-Lee Dimech
Experiment Outline • Record VLF noise at VLF eclipse site:
– Around dawn before the eclipse – Around dusk before the eclipse – Near the eclipse time of day, but on days before the eclipse – Just before, during, and just after the eclipse on that day
• Examine pre-eclipse recordings to see what differences there are in VLF noise at the different times of the day
• Examine the VLF noise recorded on eclipse day • Compare eclipse day VLF noise (before, during, and after) to VLF noise
recorded prior to the eclipse • Decide whether VLF noise at these different times (all in the same place)
are different, the same, or similar. • Decide if you can conclude whether changes in the ionosphere as a result
of the eclipse lead to conditions similar to other times when the eclipse is not taking place.
August 19, 2018: Pre-Eclipse VLF
KYBO
VLF Tent Antenna
Telescope/Camera Shelter
Projection Tent Shadow Band
Farmer’s Tent
VLF Field Site Setup
Camera/Turntable
Eclipse Day
Telescope/Camera Setup
Eclipse Projection
Tent
Eclipse Chill’n
Eclipse Event Panorama
Eclipse Day 2018 VLF
August 24, 2017 1:12 PM Around time of eclipse, but two days later.
August 24, 2017 7:53 PM After sunset same day.
0
10
20
30
40
50
60
70
80
90
-12.00 -8.00 -4.00 0.00 4.00 8.00 12.00 16.00 20.00
Sphe
ric E
vent
Rat
e (1
/s)
Relative to Event Time (min)
Aug. 19 Sunset
Aug. 21 Eclipse
Sunset Tweeks
Average flash rate within 3,000 km
Sunset
Totality
Spherics
Spherics appear little influenced by day versus night. Tweeks, which result from longer propagation paths, become common more than 3 minutes after sunset. That delay is consistent with the lack of tweek observations during totality in the 2017 eclipse. The importance of broad ionospheric modification due to darkness for tweek observation might be tested by VLF observations during the longest eclipse events.
Number of Tweeks
INSPIRE VLF Receiver Antenna Connections
Input microphone level narration or time signal
Audio microphone level output to a recorder/laptop Audio headphone out
Amplifier gain control for antenna signal and microphone “data” output.
Audio headphone output gain
Receiver power switch
Audio headphone output power switch
60 Hz hum filter switch
External power input
Switch between mic and data on CH/2
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