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Exploring the effects of solar eclipses on radio wave propagation has been an active area of research since the first experiments conducted in 1912. In the first few decades of ionospheric physics, researchers started to explore the natural laboratory of the upper atmosphere. Solar eclipses offered a rare opportunity to undertake an active experiment. The results stimulated much scientific discussion. Early users of radio noticed that propagation was different during night and day. A solar eclipse provided the opportunity to study this day/night effect with much sharper boundaries than at sunrise and sunset, when gradual changes occur along with temperature changes in the atmosphere and variations in the sun angle. Plots of amplitude time series were hypothesized to indicate the recombination rates and reionization rates of the ionosphere during and after the eclipse, though not all time-amplitude plots showed the same curve shapes. A few studies used multiple receivers paired with one transmitter for one eclipse, with a 5:1 ratio as the upper bound. In these cases, the signal amplitude plots generated for data received from the five receive sites for one transmitter varied greatly in shape. Examination of very earliest results shows the difficulty in using a solar eclipse to study propagation; different researchers used different frequencies from different locations at different times. Solar eclipses have been used to study propagation at a range of radio frequencies. For example, the first study in 1912 used a receiver tuned to 5,500 meters, roughly 54.545 kHz. We now have data from solar eclipses at frequencies ranging from VLF through HF, from many different sites with many different eclipse effects. This data has greatly contributed to our understanding of the ionosphere. The solar eclipse over the United States on August 21, 2017 presents an opportunity to have many locations receiving from the same transmitters. Experiments will target VLF, LF, and HF using VLF/LF transmitters, NIST?s WWVB time station at 60 kHz, and hams using their HF frequency allocations. This effort involves Citizen Science, wideband software defined radios, and the use of the Reverse Beacon Network and WSPRnet to collect eclipse-related data.
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On the use of solar eclipses to study the ionosphere
Exploring the effects of solar eclipses on radio wave propagation has been an active area of research since the first experiments conducted in 1912. In the first few decades of ionospheric physics, researchers started to explore the natural laboratory of the upper atmosphere. Solar eclipses offered a rare opportunity to undertake an active experiment. The results stimulated much scientific discussion. Early users of radio noticed that propagation was different during night and day. A solar eclipse provided the opportunity to study this day/night effect with much sharper boundaries than at sunrise and sunset, when gradual changes occur along with temperature changes in the atmosphere and variations in the sun angle. Plots of amplitude time series were hypothesized to indicate the recombination rates and reionization rates of the ionosphere during and after the eclipse, though not all time-amplitude plots showed the same curve shapes. A few studies used multiple receivers paired with one transmitter for one eclipse, with a 5:1 ratio as the upper bound. In these cases, the signal amplitude plots generated for data received from the five receive sites for one transmitter varied greatly in shape. Examination of very earliest results shows the difficulty in using a solar eclipse to study propagation; different researchers used different frequencies from different locations at different times. Solar eclipses have been used to study propagation at a range of radio frequencies. For example, the first study in 1912 used a receiver tuned to 5,500 meters, roughly 54.545 kHz. We now have data from solar eclipses at frequencies ranging from VLF through HF, from many different sites with many different eclipse effects. This data has greatly contributed to our understanding of the ionosphere. The solar eclipse over the United States on August 21, 2017 presents an opportunity to have many locations receiving from the same transmitters. Experiments will target VLF, LF, and HF using VLF/LF transmitters, NIST’s WWVB time station at 60 kHz, and hams using their HF frequency allocations. This effort involves Citizen Science, wideband software defined radios, and the use of the Reverse Beacon Network and WSPRnet to collect eclipse-related data.
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- Award ID(s):
- 1638685
- PAR ID:
- 10026297
- Date Published:
- Journal Name:
- 15th International Ionospheric Effects Symposium
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract During the total solar eclipse in the United States on 8 April 2024, we observed the amplitude and phase of Very Low Frequency (VLF) signals from five U.S. Navy VLF transmitters using a novel geometry of VLF receivers deployed along and across the totality path. Nine receiver sites (four of them inside the totality path) were deployed to collect the data in different transmitter‐receiver configurations relative to the totality path, which intersected with the radio propagation paths from the Cutler, MA (NAA, 24 kHz) and the LaMoure, ND (NML, 25.2 kHz) Navy transmitters. The transmitters themselves experienced 98.7% (NAA) and 68% (NML) solar obscuration at 75 km altitude. The novelty of the observations is the near‐total obscuration of one of the transmitters and observations of several radio propagation paths closely aligned to the path of totality. This configuration enabled observations of the effects of the Moon's shadow progression from Texas to Maine for over three hours on a total of 27 radio paths (with coverage from 55% to 100%) with transmitter‐to‐receiver distances ranging from 780 to 7,700 km. Both positive and negative (5–10 dB) amplitude changes were observed by receivers throughout the eclipse period. The observed phase changes were mostly negative. The unique observations of VLF propagation along the totality path produced a temporally dynamic quasiperiodic response in amplitude that can be used to determine the gradients and spatial scales of the eclipse effect on the lower ionosphere. For observations within 780 km of NAA, the eclipse produced a 13 dB surge in amplitude.more » « less
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The very first use of the solar eclipse to study the ionosphere was done in 1912 at a wavelength of 5,500 meters. Since that time, multiple studies have been done at VLF and LF frequencies. Most of these studies were performed at a single receive site with a single transmit location during a single eclipse, thus making it very hard to compare data from separate collections. This paper addresses historical collection efforts, what has been learned about the sun’s influence upon the ionosphere, and the role of neutral corpuscular particles ionizing the ionosphere. Questions raised by the above will be addressed. A planned crowdsource effort will then be described that will attempt to address and answer questions raised by having multiple receivers all reporting on signals transmitted by the same VLF/LF stations. There are two approaches to the crowdsource collection. One approach uses the SuperSID network that is already reporting on changes in propagation of signals from VLF stations. The other approach uses a receiver and antenna based upon an instrumentation amplifier chip and a smart phone as a software defined radio. The later approach will be detailed.more » « less
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We demonstrate a methodology for utilizing measurements from very low frequency (VLF, 3−30 kHz) transmitters and lightning emissions to produce 3D lower electron density maps, and apply it to multiple geophysical disturbances. The D‐region lower ionosphere (60−90 km) forms the upper boundary of the Earth‐ionosphere waveguide which allows VLF radio waves to propagate to global distances. Measurements of these signals have, in many prior studies, been used to infer path‐average electron density profiles within the D region. Historically, researchers have focused on either measurements of VLF transmitters or radio atmospherics (sferics) from lightning. In this work, we build on recently published methods for each and present a method to unify the two approaches via tomography. The output of the tomographic inversion produces maps of electron density over a large portion of the United States and Gulf of Mexico. To illustrate the benefits of this unified approach, daytime and nighttime maps are compared between a sferic‐only model and the new approach suggested here. We apply the model to characterize two geophysical disturbances: solar flares and lower ionospheric changes associated with thunderstormsmore » « less
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Abstract Very-Low-Frequency (VLF) transmitters operate worldwide mostly at frequencies of 10–30 kilohertz for submarine communications. While it has been of intense scientific interest and practical importance to understand whether VLF transmitters can affect the natural environment of charged energetic particles, for decades there remained little direct observational evidence that revealed the effects of these VLF transmitters in geospace. Here we report a radially bifurcated electron belt formation at energies of tens of kiloelectron volts (keV) at altitudes of ~0.8–1.5 Earth radii on timescales over 10 days. Using Fokker-Planck diffusion simulations, we provide quantitative evidence that VLF transmitter emissions that leak from the Earth-ionosphere waveguide are primarily responsible for bifurcating the energetic electron belt, which typically exhibits a single-peak radial structure in near-Earth space. Since energetic electrons pose a potential danger to satellite operations, our findings demonstrate the feasibility of mitigation of natural particle radiation environment.more » « less
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