Nightside Detection of a Large‐Scale Thermospheric Wave Generated by a Solar Eclipse

Abstract

The generation of a large‐scale wave in the upper atmosphere caused by a solar eclipse was first predicted in the 1970s, but the experimental evidence remains sparse and comprises mostly indirect observations. This study presents observations of the wind component of a large‐scale thermospheric wave generated by the 21 August 2017 total solar eclipse. In contrast with previous studies, the observations are made on the nightside, after the eclipse ended. A ground‐based interferometer located in northeastern Brazil is used to monitor the Doppler shift of the 630.0‐nm airglow emission, providing direct measurements of the wind and temperature in the thermosphere, where eclipse effects are expected to be the largest. A disturbance is seen in the zonal and meridional wind which is at or above the 90% significance level based on the measured 30‐day variability. These observations are compared with a first principles numerical model calculation from the Thermosphere‐Ionosphere‐Mesosphere‐Electrodynamics General Circulation Model, which predicted the propagation of a large‐scale wave well into the nightside. The modeled disturbance matches well the difference between the wind measurements and the 30‐day median, though the measured perturbation (∼60 m/s) is larger than the prediction (38 m/s) for the meridional wind. No clear evidence for the wave is seen in the temperature data, however.

Ionospheric Response to the Solar Eclipse of 21 August 2017 in Millstone Hill (42N) Observations

“…A very strong upward plasma motion with speeds up to 40 m/s higher than normal was observed for ∼2 hr after the maximum eclipse (19-21 UTC). This upward motion could be potentially caused by two contributing factors: (1) immediate (at supersonic speed) ionospheric and thermospheric heating due to recovery from the eclipse, and (2) enhanced southward and eastward (directed towards maximum shadow) wind as would be anticipated in the eclipse-induced colder thermosphere (Harding et al, 2018). This upward motion could be potentially caused by two contributing factors: (1) immediate (at supersonic speed) ionospheric and thermospheric heating due to recovery from the eclipse, and (2) enhanced southward and eastward (directed towards maximum shadow) wind as would be anticipated in the eclipse-induced colder thermosphere (Harding et al, 2018).…”

Multispectral and Multi‐instrument Observation of TIDs Following the Total Solar Eclipse of 21 August 2017

“…Neutral wind velocity derived from nighttime OI 630.0 nm (red line) emission measurements by a Fabry‐Perot interferometer in Brazil showed perturbations in neutral winds far from the path of the 21 August 2017 eclipse. Global‐scale simulations using an ultraviolet obscuration mask that mimicked the 21 August 2017 eclipse's effect on the upper atmosphere successfully predicted the measured changes (using the red line) in neutral wind qualitatively (Harding et al, ).…”

“…Besides geomagnetic storms, solar eclipses are also known to excite AGWs (e.g., Chimonas & Hines, 1970a;Liu et al, 1998) that alter the IT system (Harding et al, 2018;Lin et al, 2018). Liu et al (1998) conclude that the ionospheric perturbations that they observed using ionosondes during the total solar eclipse of 24 October 1995 were most likely due to plasma upflow and downflow induced by rapid temperature increase immediately following the eclipse.…”

The Response of the Ionosphere‐Thermosphere System to the 21 August 2017 Solar Eclipse

“…However, Harding et al (2018) done with the Thermosphere-Ionosphere-Mesosphere-Electrodynamics (TIME)-GCM. However, Harding et al (2018) done with the Thermosphere-Ionosphere-Mesosphere-Electrodynamics (TIME)-GCM.…”