Wave Steepening in Ionospheric Total Electron Density due to the 21 August 2017 Total Solar Eclipse

This study shows that a supersonic moon shadow of a total solar eclipse can steepen the ionospheric total electron content (TEC) wave on August 21, 2017. A data‐adaptive method named Hilbert‐Huang transform is employed to examine the nonlinear and non‐stationary evolution of the waves. The results show that the TEC wave behaves as a traveling ionospheric disturbance before the totality appearance, turns later into steepening, and breaks eventually. A TEC wave with a period of ∼40 min and wavelength of ∼1,000 km propagates mainly in an east‐southward direction before the totality appearance. The wave amplitude and scales, respectively, increases and reduce by near ∼50% as the moon shadow approaches the western coast of the continental United States. The short‐period TEC waves (period ∼2 min) reveal that the wave may break eventually when the wave gets steeper. The steepness of the TEC wave is reconstructed according to the constructive interference. Plain Language Summary A water wave increasing in height and shortening in wavelength as it propagating is the best‐known example of wave steepening that we often can see near the shore. For the first time, this study shows that a supersonic moon shadow of a total solar eclipse can also steepen the wave of electron density in the Earth's ionosphere over the western coast of the continental United States. The wave propagates in an east‐southward direction over Oregon and California. The evolution of electron density wave (wavelength ∼1,000 km) is similar to a big water wave for surfing in the ionosphere (Movie S1). The results suggest that the dense GNSS arrays developing in the recent decade turn the Earth's ionosphere into one of the best available outdoor laboratories for detecting and examining the wave and dynamics. Key Points The TEC wave gets steeper as the supersonic moon shadow approaches the western coast of the continental United States on August 21, 2017 The intense bow‐wave crest ahead of the moon shadow can be attributed to the constructive interference The data‐adaptive method, Hilbert‐Huang transform, benefits to extract the nonlinear and non‐stationary waves from TEC time series