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The total electron content (TEC) derived from ground‐based BeiDou geostationary orbit (GEO) satellite receivers lying on both sides of the eclipse path is used to study the ionospheric variations in southern China, particularly targeting eclipse‐induced gravity waves in the ionosphere during the annular solar eclipse on 21 June 2020. Eclipse‐induced gravity waves (GWs) signatures with periods of about 70 min, from wavelet analysis, were identified on both sides of TEC observations, which are most likely to be induced in the thermosphere. However, there were significant differences in the intensity of the gravity waves on both sides of the eclipse path, gravity waves are stronger on the northern side of the eclipse path than on the southern side. Moreover, a postponement of TEC depletion shows on the northern side of the eclipse path which is caused by the convergence effect of the wind field. And at the same obstruction rate, GWs possibly can slightly adjust the postponement of TEC depletion on a small scale. Key Points: The eclipse‐induced thermospheric gravity waves are observed by BeiDou‐geostationary orbit total electron content (TEC) on both sides of the solar eclipse pathGravity waves are stronger on the northern side of the eclipse path than that on the southern side due to convergence effectsThe gravity waves on the northern side may slightly contribute to the postponement of the TEC depletion on a small scale [ABSTRACT FROM AUTHOR]

Using meteor radar measurements at Mohe (MH, 53.5°N, 122.3°E) and the reanalysis data from 2011 to 2020, the characteristics of intraseasonal oscillations (ISOs) in the mesosphere and lower thermosphere (MLT) region over MH are investigated for the first time. The radar observation shows a prominent ISO with periods of 40–60 days in the zonal wind during the 2015/2016 winter. The observed ISO is the strongest in the oscillation period of 30–60 days during nearly a decade of observation. The ISO amplitude reaches a maximum of 16 m/s at 90 km. The vertical structure indicates that intraseasonal variabilities in the lower mesosphere contribute to the ISO in the MLT region. By bandpassing the zonal wind obtained from the reanalysis data along 122.5°E at 52 km in the Northern Hemisphere with cutoff periods of 40 and 60 days, we show that ISOs in the tropical and mid‐latitude mesosphere are related to each other. Our results also indicate that the tropical mesospheric ISO and the tropospheric Madden‐Julian Oscillations (MJO) are highly correlated. Our analysis suggests that the MJO in the equatorial troposphere may contribute to the enhancement of the ISO in the MLT region over MH. Additionally, a very strong El Niño during the 2015/2016 winter was accompanied by the positive Indian Ocean Dipole, which confines the active MJO in phases 2‒4 for a long time. This may be the reason that in the oscillation period of 30–60 days, the ISO observed at MH is the strongest during almost a decade of observation. Key Points: A strong intraseasonal oscillation (ISO) with a period of 40–60 days is first observed in the mesosphere and lower thermosphere at MoheThe ISO observed at Mohe is likely associated with the equatorial Madden‐Julian Oscillations in the troposphereStrong El Niño and the positive Indian Ocean Dipole indices may contribute to the enhancement of the ISO at MH [ABSTRACT FROM AUTHOR]

We present an analysis of planetary‐scale oscillations during sudden stratospheric warming (SSW) events based on data obtained from a meteor radar located at Mohe (MH, 53.5°N, 122.3°E), the Aura satellite and Modern‐Era Retrospective analysis for Research and Applications, Version 2 data (MERRA2). The planetary‐scale oscillations in the mesosphere and lower thermosphere (MLT) region during eight SSW events from 2012 to 2019 have been statistically investigated. Our analysis reveals that the enhancement or the generation of westward propagating quasi 16‐day oscillation with wavenumber 1 (W1) is a common feature during SSWs over MH. A strong enhancement of the quasi 4‐day oscillation during the 2018/2019 SSW is captured by both radar and satellite observations. The amplified quasi 4‐day oscillation has a period of ~4.3 days in both meridional and zonal winds and with a wavenumber of W2 in the zonal component. Using the meteor radar and MERRA2 data, the vertical structure of the quasi 4‐day oscillation from the stratosphere to the lower thermosphere is derived. The upward propagating feature of the quasi 4‐day oscillation in the meridional component indicates that the oscillation is very likely generated in the lower mesosphere. The mesospheric zonal wind reversal after an elevated stratopause event is observed during the SSW, which results in a negative meridional gradient of the quasi‐geostrophic potential vorticity. Our results not only reveal that the amplified quasi 4‐day oscillation in the MLT region is associated with the 2018/2019 SSW but also suggest that the amplification is originally generated around 60 km due to barotropic/baroclinic instability and propagates upward to MLT region. Key Points: An enhancement of a quasi 4‐day oscillation is observed in the MLT region during the 2018/2019 SSW over MHThe enhanced quasi 4‐day oscillation during 2018/2019 SSW is originally generated from the lower mesosphereThe quasi 4‐day oscillation is likely generated by barotropic/baroclinic instability due to the large zonal wind reversal and the elevated stratopause during the SSW [ABSTRACT FROM AUTHOR]