Solar Eclipse-Induced Changes in the Ozone Layer Observed with UV/VIS (UltraViolet–VISible Spectroscopy) Radiometer

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Solar eclipses are rare astronomical phenomena, which provide a natural testbed for probing processes occurring in Earth’s atmosphere. It has been reported that the Moon’s shadow as it travels over our planet during an eclipse will lead to fluctuations in the ozone layer, a result which is controversial and demands additional new research. The Earth’s ozone layer protects life on our planet from the Sun’s harmful ultraviolet (UV) radiation. This project strives to resolve this issue by performing measurements of “total ozone” (ozone amounts integrated from the Earth’s surface to the top of the atmosphere) and solar UV radiation during the total solar eclipse of 8 April 2024 with two distinct instruments. Results from the project will improve our understanding about the way radiation from the Sun travels through the atmosphere to Earth’s surface where it interacts with the living world. Apart from providing new insights in this "transfer of radiation", the project will contribute to the desire of mankind to better understand the awe-inspiring phenomenon of a solar eclipse and its implications. Furthermore, the project will advance the academic skills of an international graduate student who will simulate the irradiance during totality and compare it with the measurements. Participation of observers in Mexico and scientists from Germany at no additional costs to the project promote international collaborations.It is well established that solar eclipses generate gravity waves in the upper atmosphere (ionosphere) as the Moon’s shadow travels at supersonic speeds over Earth. However, effects on the stratospheric ozone layer are less well established, with some publications supporting a link, some disputing one, and some presenting ambiguous results because of measurement artifacts. The overarching objective of this project is to resolve these contradictions by measuring short-term (seconds to minutes) variations in the total ozone column (TOC) using “global” (Sun and sky) and direct-Sun observations in the ultraviolet (UV) range during the total solar eclipse of 8 April 2024. Measurements will be performed at Mazatlán, Mexico, under the path of totality. At this location, totality will last 4 minutes and 25 seconds and the likelihood of clear skies is one of the highest along the path of the eclipse. Global observations will be made with a GUVis-3511 radiometer, which uses 19 wavebands between 305 and 1640 nm; TOC is calculated from measurements between 305 and 340 nm. The radiometer is equipped with a shadow band to allow alternating global and diffuse measurements from which the direct spectral irradiance is calculated. A MICROTOPS II sun photometer will also be used for direct-Sun observations. Use of two distinct instruments reduces the risk that observational variations in TOC caused by measurement artifacts are incorrectly attributed to real ozone changes. Data collected as a part of this project will improve the understanding of the coupling between the upper atmosphere and the stratosphere. In addition to TOC observations, measurements of the global spectral irradiance during totality at the Earth’s surface will be compared with results of a 3-D radiative transfer model. This will enhance understanding of photon transport during a solar eclipse where photons entering the atmosphere outside the Moon’s shadow are scattered many times before reaching the observer, which is a numerically challenging problem to solve. A similar comparison during the 2017 eclipse has expanded our knowledge of the effects of surface albedo, topography, aerosols, and the vertical ozone distribution on the photon path. Data recorded during the 2024 eclipse will increase our understanding of this important effect further.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.