Ionospheric responses to the 21 August 2017 solar eclipse by using data assimilation approach

Chia-Hung Chen,Chien-Hung Charles Lin,Tomoko Matsuo

doi:10.1186/s40645-019-0263-4

Chia-Hung Chen, Chien-Hung Charles Lin + Show 1 more

Open Access

https://doi.org/10.1186/s40645-019-0263-4

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Abstract

Using the physics-based thermosphere-ionosphere model (NCAR-TIEGCM) with an ensemble Kalman filter, this study reports the first data assimilative analysis of the ionosphere responses to the solar eclipse on 21 August 2017. The system, using a 2-min assimilation cycle of data from ground-based GNSS observations, show dynamic variations of the equatorial ionization anomaly (EIA) due to the electrodynamic effects of the solar eclipse. Two major ionospheric responses are captured: (1) an early appearance of EIA at the westward boundary of moon shadow and (2) an enhanced EIA at lower latitudes and suppressed EIA at the higher latitudes. These eclipse-induced conjugate EIA variations are produced by an eastward electric field perturbation around the magnetic equator and a westward electric field perturbation at the higher latitudes.

Highlights

The solar eclipse’s effect on variations in ionospheric electron density have been investigated and reported by numerous observational and modeling methodologies (e.g., Müller-Wodarg et al 1998; Tsai and Liu 1999; Afraimovich et al 2002; Sridharan et al 2002; Tomás et al 2007, 2008, 2009; Le et al 2008, 2009; Choudhary et al 2011; St.-Maurice et al 2011; Adekoya et al 2015; Panda et al 2015; Huba and Drob 2017)
The assimilation result on the eclipse day (Fig. 1c) shows the total electron content (TEC) reduction around the northwest side of the maximum solar eclipse obscuration region
The reduction of equatorial ionization anomaly (EIA) crests at the two poleward-side regions were driven by the reverse direction of vertical plasma drifts

Summary

Introduction

The solar eclipse’s effect on variations in ionospheric electron density have been investigated and reported by numerous observational and modeling methodologies (e.g., Müller-Wodarg et al 1998; Tsai and Liu 1999; Afraimovich et al 2002; Sridharan et al 2002; Tomás et al 2007, 2008, 2009; Le et al 2008, 2009; Choudhary et al 2011; St.-Maurice et al 2011; Adekoya et al 2015; Panda et al 2015; Huba and Drob 2017). Changes in the ionospheric electrodynamic processes during solar eclipse periods is one of the most important drivers of these ionospheric variations. This is because eclipse-induced electron density changes can modify ionospheric electric conductivity and electric field distribution (Rishbeth 1968). The total solar eclipse event, 21 August 2017, occurred with a path of totality over the central USA, providing a good opportunity to investigate its effects on the photochemical and electrodynamic processes of the ionosphere. We primarily focus on two ionospheric responses to the 2017 August solar eclipse: (1) the change in the ionospheric electric field system and (2) the resulting perturbations of the conjugate EIAs

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Discussion

Conclusion