Numerical Simulations of Metallic Ion Density Perturbations in Sporadic E Layers Caused by Gravity Waves

Abstract

Tidal signatures in sporadic E (Es) layer have been confirmed by observations and simulations. However, the effect of gravity waves (GWs) on the Es layer formation process has not yet been fully understood. In this paper, the modulation of Es layers by GWs is examined through numerical simulations, in which a physics‐based model of Es layer is forced by neutral winds from the High Altitude Mechanistic General Circulation Model that can resolve GWs with horizontal wavelengths longer than 156 km (λh > 156 km). Comparison of the simulation results with and without the GWs (1,350 km > λh > 156 km) forcing reveals that the inclusion of GWs leads to short‐period (1.2–3 hr) density perturbations in Es layers, which are also seen in ground‐based ionosonde observations. At a given time, the metallic ion density at altitudes between 120 and 150 km can either increase (by up to ∼+600%) or reduce (by up to −90%) in response to GW forcing. The relative density perturbations are smaller (by up to 60%) between 90 and 120 km altitude. It is also found that the GW effect on the metallic ion density relates to the longitude, which is mostly explained by the geographical distribution of GWs activity in the mesosphere and lower thermosphere region. The longitudinal variation of the background geomagnetic field plays only a secondary role.

Enhanced Sporadic E Layer and Its Perturbations During the 2022 Hunga Volcanic Eruption

“…Strong STEC perturbation regions mainly appeared over the northwest of the epicenter after the eruption (Figure 3g), which is related to the geographical distribution of VIC that plays a key role in the formation of the Es layer (Qiu et al., 2023c; Shinagawa et al., 2017). Figure 7 shows the geographical distribution of calculated VIC averaged over 105–114 km and 117–123 km altitudes during 14–16 January 2022 by using the ICON observations.…”

“…The peak heights of the STEC perturbations mainly appear above 110 km (Figure 2b), which may be caused by the altitude dependence of the ratio of ion‐neutral collision frequency ( ν i ) to ion gyrofrequency ( ω i ). Ions converge or diverge more efficiently above 110 km (Andoh et al., 2020; Haldoupis, 2018; Qiu et al., 2023c). Qiu et al.…”

“…AGWs contribute to the production of strong neutral wind shear (Liu et al, 2014) in the MLT region, which leads to the redistribution of minor species, and they can even propagate to the ionospheric F region to cause electron density disturbances (Hickey et al, 2009;Liu et al, 2017). Using an Es layer model driven by the High Altitude Mechanistic General Circulation Model (HIAMCM) that includes the AGWs with horizontal wavelengths λ h > 156 km, Qiu et al (2023c) simulated the modulation of Es layers by AGWs and displayed the short-period perturbations in Fe + density within the Es layers.…”

“…Using an Es layer model driven by the High Altitude Mechanistic General Circulation Model (HIAMCM) that includes the AGWs with horizontal wavelengths λ h > 156 km, Qiu et al. (2023c) simulated the modulation of Es layers by AGWs and displayed the short‐period perturbations in Fe + density within the Es layers.…”

Comparison of the Heights of Sporadic E Layers and Vertical Ion Convergence Parameters

“…However, this paper suggests that IVN can better represent the height variations of Es layers. Besides the atmospheric tides of the horizontal winds, some factors also play roles in the formation and development of the Es layers (i.e., the electric fields, the diffusion, the atmospheric gravity waves, the collision frequency of ions relative to neutral species, and so on) [23,24,[39][40][41][42][43] 2020) [43]. The enhancement of collision frequency induces the Es layers to separate with IVN in the vertical direction below the altitude of 110 km [24].…”