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