submarine volcano (hereafter referred to as the Tonga volcano), which is centered at 20.546°S, 175.390°W, explosively erupted. Immense ripples on the sea surface and in the atmosphere rapidly spread outward. The volcanic explosivity index (VEI) was estimated to be 6, indicating that this eruption was one of the largest volcanic eruptions recorded in the modern era (Poli & Shapiro, 2022). The volcanic eruption released a large amount of material and energy into the atmosphere, with the highest overshooting tops of the volcanic plume reaching the lower mesosphere at an altitude of ∼55 km according to satellite imagery (Carr et al., 2022). The waves triggered by the Tonga volcanic eruption on the surface and in the ionosphere were observed worldwide by various ground-and space-based instrumentation (

On 15 January 2022, the submarine volcano on the southwest Pacific island of Tonga violently erupted. Thus far, the ionospheric oscillation features caused by the volcanic eruption have not been identified. Here, observations from the Super Dual Auroral Radar Network (SuperDARN) radars and digisondes \change{are}{were} employed to analyze ionospheric oscillations in the Northern Hemisphere caused by the volcanic eruption in Tonga. Due to the magnetic field conjugate effect, the ionospheric oscillations were observed much earlier than the arrival of surface air pressure waves, and the maximum negative line-of-sight (LOS) velocity of the ionospheric oscillations exceeded 100 m/s in the F layer. After the surface air pressure waves arrived, the maximum LOS velocity in the E layer approached 150 m/s. A maximum upward displacement of 100 km was observed in the ionosphere. This work provides a new perspective for understanding the strong ionospheric oscillation caused by geological hazards observed on Earth.

The Jiamusi (JME) radar is the first high‐frequency coherent scatter radar independently developed in China. In this study, we investigate the statistical characteristics of the Jiamusi radar scattering occurrence rate from the F‐region ionosphere between 40°N and 65°N geomagnetic latitude (MLAT) from March 2018 to November 2019. Then, the diurnal and seasonal variations in scattering echoes and their dependence on geomagnetic conditions are statistically investigated. It is shown that the local time of the peak scattering occurrence rate varies depending on the seasons, that is, approximately 20–22.5 magnetic local time (MLT) in summer, 17.5–20.5 MLT in equinox, and 16–17.5 MLT in winter, which is closely associated with the time of sunset. The occurrence rate also increases with the enhancement of the Kp index. To further understand the mechanism of these features, we simulate the distribution of the gradient drift instability (GDI) indicator ∇n·trueV→/n $\nabla n\cdot \overrightarrow{V}/n$ by using the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM). The analysis results indicate that the GDI may be one of the factors that contribute to these characteristic features.

The Jiamusi (JME) radar is the first high-frequency coherent scatter radar independently developed in China. In this study, we investigate the statistical characteristics of the occurrence rate of F-region ionospheric irregularities between 40°N and 65°N geomagnetic latitude by using the Jiamusi radar data from March 2018 to November 2019. Diurnal and seasonal variations in scattering echoes and their dependence on geomagnetic conditions are statistically investigated. It is shown that the local time of the peak echo occurrence rate varies depending on the season, i.e., approximately 20-22.5 magnetic local time (MLT) in summer, 17.5-20.5 MLT in equinox, and 16-17.5 MLT in winter, which is closely associated with the time of sunset. The echo occurrence rate also increases with the enhancement of the geomagnetic index. To further understand the mechanism of these features, we simulate the distribution of the gradient drift instability indicator ([?]n * V E /n) by using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). The analysis results indicate that the gradient drift instability is an important mechanism for irregularities in this region. Key points: 1. Diurnal and seasonal variations in the scatter occurrence rate and their dependence on Kp conditions are statistically analyzed. 2. The distribution of the gradient drift instability indicator ([?]n * V E /n) is simulated by using the TIEGCM. 3. The gradient drift instability is an important mechanism for the high occurrence rate of echoes in the midlatitude region.