Imaging the D-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.