The Altitudinal Dependences of the Inter‐Hemispheric Asymmetry in the Mid‐Latitude Ionospheric Post‐Midnight Enhancement During Equinox

Abstract

Using observations from multi‐satellites at different altitudes, including the CHAllenging Minisatellite Payload (CHAMP), the Gravity Recovery and Climate Experiment, Swarm B, and Defense Meteorological Satellites Program F17, the ionospheric post‐midnight enhancement at mid‐latitudes and the associated inter‐hemispheric asymmetry during equinox are investigated in this study. During equinox months, the ionospheric electron density enhancement during post‐nighttime at mid‐latitudes is visible in both hemispheres, however, it is asymmetric between the Northern and Southern Hemispheres. At most longitudes, inter‐hemispheric asymmetry of Mid‐latitude Ionospheric Post‐midnight Enhancement (MIPE) reverses with altitudes, from a stronger electron density in the Northern Hemisphere at CHAMP altitude to a stronger electron density in the Southern Hemisphere at top ionosphere during equinox. The reversal altitude and reversal time have significant longitudinal differences. The effective ionospheric uplifting induced by the combination of neutral winds and geomagnetic field configuration is the main contribution to the asymmetry reversal of MIPE at lower altitudes, as shown in the simulations from the SAMI2 and HWM14 models. In comparison with that in the Southern Hemisphere, the stronger neutral winds in the Northern Hemisphere move the plasma along the geomagnetic field lines to a higher altitude with lower chemical recombination, resulting in the enhancement of electron density.

The Middle and Low Latitude Ion Composition Variations Observed by the DMSP Satellites on 20–31 August 2018

“…The present DMSP observations showed that the H + was the dominant ion at ∼4 LT at 840 km altitude and its latitude profiles presented two peaks around 40°N/S during the quite times on 20-24 August 2018. The previous studies showed that the nighttime ionosphere was not always decreased monotonously after the cease of the sunlit, and it sometimes presented enhancement in middle latitudes (e.g., Xiong & Lühr, 2014;Chen et al, 2015;Zhang et al, 2024;Zhong et al, 2019). Several mechanisms are suggested to induce the nighttime enhancement of the ionosphere F2 region, including the equatorward neutral wind and the downward flux from the plasmasphere and topside ionosphere (e.g., Chen et al, 2011;Jee et al, 2005;Kotov et al, 2016).…”

Statistical Investigation of the Storm Time Plasma Density Strip-like Bulges at Lower-Mid Latitudes

“…The latter indication is due to the constitutional difference between the two structures. The midlatitude extra peaks could be observed down to the CHAMP altitude below 400 km (Zhang et al, 2024), indicating that the ionospheric O + plays a dominant role. In addition, we examined several DMSP extra peak cases and found O + dominance (not shown).…”