The westward quasi‐6‐day wave (Q6DW) with zonal wavenumber 1 is a prominent and recurrent phenomenon in the mesosphere and lower thermosphere (MLT) and has a significant impact on day‐to‐day ionospheric variability. Geopotential height measurements from Aura Microwave Limb Sounder and Specified Dynamics Whole Atmosphere Community Climate Model eXtended Version simulations during 2005–2019 are utilized to study the climatological variations of Q6DW. The spectral analysis clearly indicates that four typical Q6DW events occur in the MLT region before and after the two equinoxes in 1 year. The wave amplitudes in the summer hemisphere are considerably larger than the amplitudes in the winter hemisphere. The Eliassen‐Palm flux diagnostics show that the wave source of the post‐September equinox event is located in both hemispheres, while the sources of the other three Q6DW events are in the winter hemisphere. The diagnostic analysis results show that the climatological features of Q6DW are primarily due to the seasonal variations of the mean flow, which can determine the Q6DW critical layers, baroclinic/barotropic instability, and waveguides. Specifically, the Q6DW can be amplified in the summer hemisphere mesosphere at high latitudes during pre‐ and postequinox periods when the critical layers penetrate the unstable region. At the two equinoxes, the Q6DW can also propagate into the MLT region with similar amplitudes in both hemispheres due to the weak zonal mean flow but without additional amplification. At the two solstices, the Q6DW is suppressed because the critical layers envelop the whole unstable region, which prevents its amplification through wave‐mean flow interaction.

We studied the correlations between the migrating and non-migrating tides and solar cycle in the mesosphere and lower thermosphere (MLT) regions between 60$°$S and 60$°$N, which are in LAT-LON Earth coordinates, by analyzing the simulation datasets from the thermosphere and ionosphere extension of the Whole Atmosphere Community Climate Model (WACCM-X). A least squares fitting method was utilized to obtain the daily mean migrating tides and non-migrating tides. The Pearson linear correlation coefficient was used to analyze the correlations between tides and solar activity. Our analysis shows that the negative correlations between tides and solar activity are mostly impacted by the first symmetrical structure of the tidal modes for both migrating and non-migrating components. The coefficient of molecular thermal conductivity for the first symmetrical structure is small at low solar flux, so the tides dissipate more slowly when the F10.7 cm radio flux level is low. Thus, the amplitudes of tidal variations under a solar minimum condition are larger than those under a solar maximum condition. The correlation between tides and solar activity could also be influenced by some other factors, such as geomagnetic activity and the density of carbon dioxide $\left({\mathrm{CO}}_2\right)$ on Earth. The tidal variations can be influenced by westward background wind, which grows stronger as geomagnetic activity rises. Further, dissipation of the tides decreases because the heat conduction and molecular viscosity are weakened in the cooling thermosphere caused by increasing ${\mathrm{CO}}_2$, which results in larger tidal amplitudes under the solar maximum condition. It is found that the correlations between tides and solar cycle vary at different altitudes and latitudes. The negative correlations are most possibly influenced by the first symmetrical structure of tidal variations and may also be impacted by geomagnetic activity. The positive correlations are impacted by the density of ${\mathrm{CO}}_2$.

We present the climatology of mesopause temperatures using high‐latitude and middle‐latitude meteor radars. The daily mesopause temperatures are estimated using ambipolar diffusion coefficient data from the meteor radars at Davis Station (68.6°S, 77.9°E), in Antarctica, Svalbard (78.3°N, 16°E), Tromsø (69.6°N, 19.2°E) in the Arctic, and Mohe (53.5°N, 122.3°E) and Beijing (40.3°N, 116.2°E) in the northern middle latitudes. The seasonal variations in the meteor radar‐derived temperatures are in good agreement with the temperatures from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the TIMED satellite. Interhemispheric observations indicate that the mesopause temperatures over the southern and northern polar regions show a clear seasonal asymmetry. The seasonal variations in the Davis Station meteor radar temperatures in the southern polar mesopause are dominated by an annual oscillation (AO) with a relatively weak semiannual oscillation (SAO), which show a clear minimum during summer and a maximum during winter. The mesopause temperatures in the northern high and middle latitudes observed by the Svalbard, Tromsø, Mohe, and Beijing meteor radars mainly show an AO, with a maximum during winter and a minimum during summer. The AO in the northern polar regions is stronger than that in the southern polar regions, while the SAO in the southern polar regions is relatively strong compared to that in the northern polar regions.

The accurate prediction of atmospheric wind speed in near space is of importance for both middle and upper atmospheric scientific research and engineering applications. In order to improve the accuracy of short-term wind speed predictions in near space, this paper proposes a multi-step hybrid prediction method based on the combination of variational modal decomposition (VMD), particle swarm optimization (PSO) and long short-term memory neural networks (LSTM). This paper uses the measurement of wind speed in the height range of 80–88 km at the Kunming site (25.6° N, 103.8° E) for wind speed prediction experiments. The results show that the root mean square error ($RMSE$) and the mean absolute percentage error ($MAPE$) of multi–step wind predictions are less than 6 m/s and 15%, respectively. Furthermore, the proposed VMD–PSO–LSTM method is compared with the traditional seasonal difference autoregressive sliding average model (SARIMA) to investigate its performance. Our analysis shows that the percentage improvement of prediction performance compared to the traditional time series prediction model can reach at most 85.21% and 83.75% in $RMSE$ and $MAPE$, respectively, which means that the VMD–PSO–LSTM model has better accuracy in the multi-step prediction of the wind speed.

The Hunga Tonga–Hunga Ha′apai volcano erupted on 15 January 2022, launching Lamb waves and gravity waves into the atmosphere. In this study, we present results using 13 globally distributed meteor radars and identify the volcanogenic gravity waves in the mesospheric/lower thermospheric winds. Leveraging the High-Altitude Mechanistic general Circulation Model (HIAMCM), we compare the global propagation of these gravity waves. We observed an eastward-propagating gravity wave packet with an observed phase speed of 240 ± 5.7 m s⁻¹ and a westward-propagating gravity wave with an observed phase speed of 166.5 ± 6.4 m s⁻¹. We identified these waves in HIAMCM and obtained very good agreement of the observed phase speeds of 239.5 ± 4.3 and 162.2 ± 6.1 m s⁻¹ for the eastward the westward waves, respectively. Considering that HIAMCM perturbations in the mesosphere/lower thermosphere were the result of the secondary waves generated by the dissipation of the primary gravity waves from the volcanic eruption, this affirms the importance of higher-order wave generation. Furthermore, based on meteor radar observations of the gravity wave propagation around the globe, we estimate the eruption time to be within 6 min of the nominal value of 15 January 2022 04:15 UTC, and we localized the volcanic eruption to be within 78 km relative to the World Geodetic System 84 coordinates of the volcano, confirming our estimates to be realistic.

A rare minor sudden stratospheric warming is observed in the Antarctic polar region during September 2019, which results in the enhancement of a westward wavenumber 1 quasi‐6‐day wave (Q6DW) in the mesopause region. The impacts of this Q6DW event to the ionosphere are then comparatively investigated with multiple data sets, including the ground‐based total electron content (TEC) from geostationary BeiDou satellite receivers and F2 layer maximum frequency (foF2) from ionosondes ranging from 20 to 40°N over eastern Asia. Besides, the global TEC maps from the International Global Navigation Satellite Systems Service (IGS) are also utilized to study the longitudinal variations. The ground‐based TEC and foF2 observations clearly shows planetary wave (PW) signals with a similar period as those in the mesosphere, which are further verified to be westward with zonal wavenumber 1 by IGS TEC maps. The ground‐based TEC and foF2 also show that the peak of the ionospheric response is at around 1,200–1,400 LT and 25°N over eastern Asia with maximum amplitudes of ∼9 TECU and ∼1.5 MHz, respectively, which are also well captured by IGS TEC maps. Nevertheless, the wave amplitudes exhibited by ground‐based TEC are 2–3 times larger than that in IGS TEC. Besides, the IGS TEC map shows that the ionospheric oscillations at different longitudes peak in the equatorial ionospheric anomaly crest region at similar solar local time, but with significant variabilities in their amplitude. Our analysis shows that the ground‐based ionospheric observations and IGS TEC maps generally exhibit consistent latitudinal structures on the neutral‐ion coupling through PWs.