Hemispherically Asymmetric Evolution of Nighttime Ionospheric Equatorial Ionization Anomaly in the American Longitude Sector

Abstract

The Global‐scale Observation of Limb and Disk (GOLD) mission observed distinct post‐sunset, hemispherically asymmetric evolution of the equatorial ionization anomaly between 40° and 50°W on 19 November 2018, with the southern crest shifting poleward but the northern crest remaining in the same latitude region. The Whole Atmosphere Community Climate Model‐eXtended captured this phenomenon. Diagnostic analysis revealed that this asymmetric evolution was due to the hemispheric asymmetry in plasma transport by E × B drifts and neutral winds. In the Northern hemisphere, northward neutral wind transport dominated around sunset (20 UT near 45°W), causing the crest to be at lower altitudes and decay faster. After pre‐reversal enhancement (PRE) occurred at 20 UT in the northern hemisphere, E × B and neutral wind transport largely balanced each other, and the crest remained in the same latitude region. In the southern hemisphere EIA crest, PRE occurred around 1 hr later than the one in the north. The northward neutral wind transported the plasma to higher altitudes with less recombination. E × B transport augmented the neutral wind transport after 21 UT, lifting and pushing the crest poleward. The magnetic field configuration (large declination) and the resultant occurrence time difference in PRE between 40°W and 50°W not only play critical roles in the asymmetric evolution of the two crests, but also makes it possible for this phenomenon to be observed in the GOLD field‐of‐view.

Investigation of the ΣO/N2 Depletion With Latitudinally Tilted Equatorward Boundary Observed by GOLD During the Geomagnetic Storm on April 20, 2020

“…The GOLD Far Ultraviolet imager flies onboard the SES-14 telecommunications satellite, which was launched on 25 January 2018 to the geostationary orbit at 47.5 𝐴𝐴 • W (Eastes et al, 2017). GOLD measures the thermospheric/ionospheric airglow emissions from 134 to 162 nm with a spectral resolution of 0.2 nm during daytime (Eastes et al, 2020) and with a spectral resolution of 0.4 nm at nighttime (Cai et al, 2022a(Cai et al, , 2022bEastes et al, 2019) (Yu et al, 2022). In this study, GOLD observed 𝐴𝐴 Σ O/N 2 in the Northern Hemisphere (NH) with a spatial resolution of 1° × 1° on DOY 110 and 111 are utilized.…”

“…The GOLD Far Ultraviolet imager flies onboard the SES‐14 telecommunications satellite, which was launched on 25 January 2018 to the geostationary orbit at 47.5$${}^{\circ}$$W (Eastes et al., 2017). GOLD measures the thermospheric/ionospheric airglow emissions from 134 to 162 nm with a spectral resolution of 0.2 nm during daytime (Eastes et al., 2020) and with a spectral resolution of 0.4 nm at nighttime (Cai et al., 2022a, 2022b; Eastes et al., 2019). The daytime OI 135.6 nm and N 2 LBH bands (140–150 nm) are utilized to derive $${\Sigma}$$O/N 2 , of which images are in the same regions between 120$${}^{\circ}$$W and 20$${}^{\circ}$$E, 60$${}^{\circ}$$S and 60$${}^{\circ}$$N from 6:10 to 22:40 UT every day (Yu et al., 2022).…”

Mid‐Latitude Ionospheric Response to a Weak Geomagnetic Activity Event During Solar Minimum

“…It should be noted that the density of O + ions is almost equal to the electron density (Ne) in the ionosphere F2 region. The O + and electron densities in the ionosphere F2 region are determined by the following equation (Cai et al, 2022a(Cai et al, , 2022bJ. Liu, Wang, Burns, Solomon, et al, 2016)…”

“…It should be noted that the density of O + ions is almost equal to the electron density (Ne) in the ionosphere F2 region. The O + and electron densities in the ionosphere F2 region are determined by the following equation (Cai et al., 2022a, 2022b; J. Liu, Wang, Burns, Solomon, et al., 2016) $$$\frac{\partial {N}_{{O}^{+}}}{\partial t}={q}_{{O}^{+}}-\beta {N}_{{O}^{+}}-\nabla \cdot \left({N}_{{O}^{+}}\stackrel{\rightharpoonup }{V}\right)$$$ where $$\partial {N}_{{O}^{+}}/\partial t$$ stands for the change rate of the O + density; $${q}_{{O}^{+}}$$ is the chemical production rate; $$\beta {N}_{{O}^{+}}$$ is the loss rate; $$\nabla \cdot \left({N}_{{O}^{+}}\stackrel{\rightharpoonup }{V}\right)$$ includes plasma transport due to neutral winds, E × B drift, and ambipolar diffusion. For convenience, the O + density change rate ( δO + ) induced by chemical production and loss rates, neutral wind transport, E × B transport, and ambipolar diffusion are termed as $$\delta {O}_{\mathrm{C}\mathrm{h}\mathrm{e}\mathrm{m}}^{+}$$, $$\delta {O}_{\mathrm{W}\mathrm{i}\mathrm{n}\mathrm{d}}^{+}$$, $$\delta {O}_{\mathrm{E}\times \mathrm{B}}^{+}$$, and …”

Diagnostic Analysis of the Physical Processes Underlying the Long‐Duration O/N2 Depletion During the Recovery Phase of the 8 June 2019 Geomagnetic Storm

“…The GOLD instrument is onboard the SES‐14 telecommunications satellite which was launched on 25 January 2018 to geosynchronous orbit at a longitude of 47.5$${}^{\circ}$$W (Eastes et al., 2017). GOLD observes thermospheric/ionospheric Far Ultraviolet airglow emissions on the Earth's limb and disk from 134 to 162 nm with a high spectral resolution of 0.2 nm (Eastes et al., 2017, 2020) during daytime and a spectral resolution of 0.35 nm during nighttime (Cai et al., 2022a, 2022b; Eastes et al., 2019). The observed OI 135.6 nm and LBH bands are inverted to derive daytime $${\Sigma}$$O/N 2 (Correira et al., 2021; Strickland et al., 1995).…”