Hemispherically Asymmetric Evolution of Nighttime Ionospheric Equatorial Ionization Anomaly in the American Longitude Sector. Issue 11 (5th November 2022)

• Record Type: Journal Article
• Authors: Cai, Xuguang; Qian, Liying; Wang, Wenbin; McInerney, Joseph M.; Liu, Han‐Li; Eastes, Richard W.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 11(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-11-05
• Subjects: equtorial ionization anomaly -- ionosphere -- asymmetry -- EcrossB drift; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2022JA030706
• Languages: English
• ISSNs: 2169-9380

Abstract

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. Plain Language Summary: A whole atmosphere model from the Earth's surface to the upper thermosphere (∼600 km) quantitively reproduced a hemispherically asymmetric movement of equatorial ionization anomaly (EIA) crests (between 40°W and 50°W; 22–24 UT on 19 November 2018) observed by the airglow measurements on a geo‐stationary satellite. Model results revealed that the neutral winds transported the plasma toward the magnetic equator and higher altitudes with less chemical loss in the southern hemisphere, whereas opposite condition occurred in the northern hemisphere between 19 and 21 UT. Consequently, ionospheric F‐peak height (hmF2) of the EIA in the southern hemisphere was much higher than that in the northern hemisphere. After 20 UT, pre‐reversal enhancement (PRE) appeared in the northern hemisphere. It offsets the transport due to field‐aligned wind in the vertical direction, which made the northern crest stationary. However, PRE appeared 1‐hr later in the southern hemisphere. The transport by E × B drifts in the southern EIA region augmented field‐aligned wind transport, lifting the southern EIA crest and shifting it poleward. The local time difference of the PRE occurrence in the two hemispheres drive this hemispherically asymmetric movement of EIA from 22 to 24 UT, which was observed by the geo‐stationary satellite. Key Points: Whole Atmosphere Community Climate Model‐eXtended simulation captures the Global‐scale Observation of Limb and Disk observed postsunset equatorial ionization anomaly (EIA) asymmetric evolution near 45°W longitude The offset of E × B drifts and neutral wind transport and strong recombination at lower altitude keep the northern crest at the same latitude Pre‐reversal enhancement occurs 1 hr later in the south and augments neutral wind transport to lift the EIA crest and shift it poleward