Imaging the <i>D</i> ‐Region Ionosphere During the 2017 Total Solar Eclipse Using VLF Measurements

Abstract The very‐low‐frequency (VLF) technique has been traditionally utilized to remotely sense the D ‐region ionosphere, but mostly for the average condition along the transmitter‐receiver path, which is insufficient for atmospheric and space weather studies. The Kalman filter has thus been utilized to infer the D ‐region ionosphere over large areas. However, the inversion of D ‐region ionosphere using VLF measurements is highly nonlinear, and the Kalman filter is not suitable for this problem. Therefore, we have recently developed a method to image the D ‐region ionosphere using a particle filter and VLF measurements from a network of receivers. In this study, we verify this method using the VLF measurements during the solar eclipse that occurred at 16:48‐20:01 UT on 21 August 2017 and present, for the first time, 2‐D images of D ‐region ionosphere over the continental United States during this eclipse. The inversion results are highly consistent with previous studies and well‐known facts: the variation of reflection height and electron density closely followed the movement of the umbra shadow, and recovered to the pre‐eclipse conditions as the eclipse passed. The increase in reflection height was approximately 4.3 km during the solar eclipse, and the electron density had a maximum reduction of 79.4%. Moreover, the electron density of D ‐region ionosphere is also consistent with the obscuration factor in the extreme ultraviolet wavelength range. Our results have reconstructed the disturbance of D ‐region ionosphere caused by the 2017 solar eclipse. Therefore, this method is reliable and can be further utilized to image the D ‐region ionosphere with network measurements of VLF transmitter signals.