Ionospheric bow waves and perturbations induced by the 21 August 2017 solar eclipse

Abstract

During solar eclipses, the Moon's shadow causes a large reduction in atmospheric energy input, including not only the stratosphere but also the thermosphere and ionosphere. The eclipse shadow has a supersonic motion which is theoretically expected to generate atmospheric bow waves, similar to a fast‐moving river boat, with waves starting in the lower atmosphere and propagating into the ionosphere. However, previous geographically limited observations have had difficulty detecting these weak waves within the natural background atmospheric variability, and the existence of eclipse‐induced ionospheric waves and their evolution in a complex coupling system remain controversial. During the 21 August 2017 eclipse, high fidelity and wide coverage ionospheric observations provided for the first time an oversampled set of eclipse data, using a dense network of Global Navigation Satellite System receivers at ∼2,000 sites in North America. We show the first unambiguous evidence of ionospheric bow waves as electron content disturbances over central/eastern United States, with ∼1 h duration, 300–400 km wavelength and 280 m/s phase speed emanating from and tailing the totality region. We also identify large ionospheric perturbations moving at the supersonic speed of the maximum solar obscuration which are too fast to be associated with known gravity wave or large‐scale traveling ionospheric disturbance processes. This study reveals complex interconnections between the Sun, Moon, and Earth's neutral atmosphere and ionosphere and demonstrates persistent coupling processes between different components of the Earth's atmosphere, a topic of significant community interest.

<i>Plain Language Summary</i>: During solar eclipses, the Moon's shadow causes a large reduction in atmospheric energy input, including the stratosphere and both the thermosphere and ionosphere (∼100–1,000 km altitudes). Theoretical studies since the 1960s have predicted that the Moon's supersonic shadow should generate atmospheric bow waves, similar to a fast‐moving river boat. However, observations were geographically limited for these weak and complicated waves. In 2017, high fidelity and wide coverage ionospheric observations were made using a North American Global Navigation Satellite System (GNSS) ∼2,000 receiver network. Eclipse passage generated clear ionospheric bow waves in electron content disturbances emanating from totality primarily over central/eastern United States. Study of wave characteristics reveals complex interconnections between the Sun, Moon, and Earth's neutral atmosphere and ionosphere.