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1. Does total column ozone change during a solar eclipse?

   https://doi.org/10.5194/acp-25-819-2025  

   Bernhard, Germar H; Janson, George T; Simpson, Scott; Cordero, Raúl R; Sepúlveda_Araya, Edgardo I; Jorquera, Jose; Rayas, Juan A; Lind, Randall N (January 2025, Atmospheric Chemistry and Physics)

   Kazadzis, Stelios (Ed.)

   Abstract. Several publications have reported that total column ozone (TCO) may oscillate with an amplitude of up to 10 DU (Dobson units) during a solar eclipse, whereas other researchers have not seen evidence that an eclipse leads to variations in TCO beyond the typical natural variability. Here, we try to resolve these contradictions by measuring short-term variations (of seconds to minutes) in TCO using “global” (Sun and sky) and direct-Sun observations in the ultraviolet (UV) range with filter radiometers (GUVis-3511 and Microtops II®). Measurements were performed during three solar eclipses: the “Great American Eclipse” of 2024, which was observed in Mazatlán, Mexico, on 8 April 2024; a partial solar eclipse that took place in the United States on 14 October 2023 and was observed at Fort Collins, Colorado (40.57° N, 105.10° W); and a total solar eclipse that occurred in Antarctica on 4 December 2021 and was observed at Union Glacier (79.76° S, 82.84° W). The upper limits of the amplitude of oscillations in TCO observed at Mazatlán, Fort Collins, and Antarctica were 0.4 %, 0.3 %, and 0.03 %, respectively. The variability at all sites was within that observed during times not affected by an eclipse. The slightly larger variability at Mazatlán is due to cirrus clouds occurring throughout the day of the eclipse and the difficulty of separating changes in the ozone layer from cloud effects. These results support the conclusion that a solar eclipse does not lead to variations in TCO of more than ± 1.2 DU and that these variations are likely much lower, drawing into question reports of much larger oscillations. In addition to calculating TCO, we also present changes in the spectral irradiance and aerosol optical depth during eclipses and compare radiation levels observed during totality. The new results augment our understanding of the effect of a solar eclipse on the Earth's upper atmosphere. 

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2. On the use of solar eclipses to study the ionosphere

   Liles, W; Mitchell, C.; Cohen, M.; Earle, G.; Frissell, N.; Kirby-Patel, K.; Lukes, L.; Miller, E.; Moses, M.; Nelson, J.; et al (May 2017, 15th International Ionospheric Effects Symposium)

   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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3. On the use of solar eclipses to study the ionosphere

   Liles, W; Mitchell, C.; Cohen, M.; Earle, G.; Frissell, N.; Kirby-Patel, K.; Lukes, L.; Miller, E.; Moses, M.; Nelson, J.; et al (January 2017, 15th International Ionospheric Effects Symposium)

   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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4. Cooling the Coldest Continent: The 4 December 2021 Total Solar Eclipse over Antarctica

   https://doi.org/10.1175/BAMS-D-22-0272.1  

   Garreaud, René; Bozkurt, Deniz; Spangrude, Carl; Carrasco-Escaff, Tomás; Rondanelli, Roberto; Muñoz, Ricardo; Jubier, Xavier M.; Lazzara, Matthew; Keller, Linda; Rojo, Patricio (December 2023, Bulletin of the American Meteorological Society)

   Abstract Total solar eclipses (TSEs) are impressive astronomical events that have attracted people’s curiosity since ancient times. Their abrupt alterations to the radiation balance have stimulated studies on “eclipse meteorology,” most of them documenting events in the Northern Hemisphere while only one TSE (23 November 2003) has been described over Antarctica. On 4 December 2021—just a few days before the austral summer solstice—the moon blocked the sun over the austral high latitudes, with the path of totality arching from the Weddell Sea to the Amundsen Sea, thus producing a ∼2-min central TSE. In this work we present high-resolution meteorological observations from Union Glacier Camp (80°S, 83°W), the only location with a working station under totality, and South Pole station. These observations were complemented with meteorological records from 37 surface stations across Antarctica. Notably, the largest cooling (∼5°C) was observed over the East Antarctic dome, where obscurity was ∼85% while many sectors experienced insignificant temperature changes. This heterogenous cooling distribution, at odds with the seemingly homogeneous land surface of Antarctica, is partially captured by a simple radiative model. To further diagnose the effect of the eclipse on the surface meteorology, we ran multiple pairs of simulations (eclipse enabled and disabled) using the Weather Research and Forecasting (WRF) Model. The overall pattern and magnitude of the simulated cooling agree well with the observations and reveal that, in addition to the solar radiation deficit and cloud cover, low-level winds and the height of the planetary boundary layer are key determinants of the temperature changes and their spatial variability. 

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5. Observations and Modeling Studies of Solar Eclipse Effects on Oblique High Frequency Radio Propagation

   https://doi.org/10.1029/2020SW002560  

   Moses, M. L.; Kordella, L. J.; Earle, G. D.; Drob, D.; Huba, J. D.; Ruohoniemi, J. M.; Shepherd, S. G.; Sivakumar, V. (March 2021, Space Weather)

   Abstract The total solar eclipse over the continental United States on 21 August 2017 offered a unique opportunity to study the dependence of the ionospheric density and morphology on incident solar radiation at different local times. The Super Dual Auroral Radar Network (SuperDARN) radars in Christmas Valley, Oregon, and Fort Hays, Kansas, are located slightly southward of the line of totality; they both made measurements of the eclipsed ionosphere. The received power of backscattered signal decreases during the eclipse, and the slant ranges from the westward looking radar beams initially increase and then decrease after totality. The time scales over which these changes occur at each site differ significantly from one another. For Christmas Valley the propagation changes are fairly symmetric in time, with the largest slant ranges and smallest power return occurring coincident with the closest approach of totality to the radar. The Fort Hays signature is less symmetric. In order to investigate the underlying processes governing the ionospheric eclipse response, we use a ray‐tracing code to simulate SuperDARN data in conjunction with different eclipsed ionosphere models. In particular, we quantify the effect of the neutral wind velocity on the simulated data by testing the effect of adding/removing various neutral wind vector components. The results indicate that variations in meridional winds have a greater impact on the modeled ionospheric eclipse response than do variations in zonal winds. The geomagnetic field geometry and the line‐of‐sight angle from each site to the Sun appear to be important factors that influence the ionospheric eclipse response. 

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