Publisher：Space Weather  

Sporadic E (Es) layers are plasma irregularities significantly affecting radio communication and navigation systems. And, their dominant formation mechanism at mid-latitudes, known as the wind shear theory, suggests that they serve as indicators of the atmosphere-ionosphere coupling processes in the mesosphere and lower thermosphere region. On 15 January 2022, the Hunga Tonga-Hunga Ha'api submarine volcanic eruption provided a unique opportunity to investigate the Es layer responses to lower atmospheric perturbations. Using the FORMOSAT-7/COSMIC-2 radio occultation and ground-based ionosonde observations, this study reveals the spatial-temporal behaviors of the Es layers after the Hunga volcanic eruption. The results show that significant Es layer perturbations occurred over the northwest of the epicenter ∼4 hr after the eruption and lasted for approximately ∼22 hr. We also calculated the geographical distribution of the vertical ion convergence (VIC) using neutral winds obtained from the Michelson Interferometer for Global High-resolution Thermospheric Imaging on the Ionospheric Connection Explorer (ICON) satellite. A comparison of the geographical distribution of positive VIC and Es layer perturbations shows a good agreement, which indicates that the enhanced Es layers are caused by strong VIC associated with the atmospheric perturbations due to the eruption. This study presents observational evidence for coupling between the Es layer and lower atmospheric perturbations, which can be helpful for understanding the occasionality and variability of Es layer occurrence.

DOI： 10.1029/2023SW003837

Web of Science

Scopus

Publisher：Remote Sensing  

Sporadic E (Es) layers are thin layers of enhanced electron density that commonly appear at altitudes of 90–130 km, often impacting radio communications and navigation systems. The wind shear theory posits that the vertical ion drift, influenced by atmospheric neutral winds and the magnetic field, serves as a significant dynamic driver for the formation and movement of Es layers. In current studies, both the heights of ion vertical velocity null (IVN) and the maximum vertical ion convergence (VICmax) have been proposed as the potential height of Es layer occurrence. In this study, utilizing the neutral atmospheric wind data derived from the WACCM-X (The Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension), we computed and compared these two parameters with the observed Es layer heights recorded by the FORMOSAT-3/COSMIC (FORMOsa SATellite-3/Constellation Observing System for Meteorology, Ionosphere, and Climate) radio occultation (RO) observations. The comparative analysis suggests that IVN is a more likely node for Es layer occurrence than VICmax. Subsequently, we examined the height–time distributions of IVN and Es layers, as well as their respective descent rates at different latitudes. These results demonstrated a notable agreement in height variations between IVN and Es layers. The collective results presented in this paper provide strong support that the ion vertical velocity null plays a crucial role in determining the height of Es layers.

DOI： 10.3390/rs15245674

Web of Science

Scopus

Publisher：Earth and Planetary Physics  

At present, the main detection instruments for observing sporadic E (Es) layers are ground-based radars, dense networks of ground-based global navigation satellite system (GNSS) receivers, and GNSS radio occultation, but they cannot capture the whole picture of the horizontal structure of Es layers. This study employs the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension model (WACCM-X 2.1) to derive the horizontal structure of the ion convergence region (HSICR) to explore the shapes of the large-scale Es layers over East Asia for the period from June 1 to August 31, 2008. The simulation produced the various shapes of the HSICRs elongated in the northwest−southeast, northeast−southwest, or composed of individual small patches. The close connection between Es layer critical frequency (foEs) and vertical ion convergence indicates that the HSICR is a good candidate for revealing and explaining the horizontal structure of the large-scale Es layers.

DOI： 10.26464/epp2023071

Web of Science

Scopus

Publisher：Journal of Geophysical Research: Space Physics  

In previous studies, various physical parameters, such as vertical wind shear null, vertical ion velocity null (IVN), and maximum gradient of vertical ion velocity, have been used as an indicator of Es layer height in light of the wind shear theory. Using a numerical Es layer model, we investigated which parameter represents the height of Es layer over Wuhan (114.4°E, 30.5°N) most precisely. The simulation results show that the height of Es layer above 110 km depends most strongly on the height of vertical IVN. However, below 110 km, the height of vertical IVN does not always agree with the height of Es layer. The analysis of simulation results suggests that the vertical gradient of the ratio of the ion-neutral collision frequency (νi) to the ion gyrofrequency (ωi) affects the Es layer formation at lower altitudes (below 110 km). We also examined the effect of electric fields on the height and intensity of Es layers over Wuhan. It is found that eastward/upward electric fields can lift the Es layer height and reduce the Es layer intensity.

DOI： 10.1029/2023JA031508

Web of Science

Scopus

Publisher：Earth and Space Science  

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.

DOI： 10.1029/2023EA003030

Web of Science

Scopus