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Atmospheric gravity waves (GWs) can strongly modulate middle atmospheric circulation and can be a significant factor for the coupling between the lower atmosphere and the middle atmosphere. GWs are difficult to resolve in global atmospheric models due to their small scale; thus, GW observations play an important role in middle atmospheric studies. The climatology of GW variance and momentum in the low-latitude mesosphere and lower thermosphere (MLT) region are revealed using multiple meteor radars, which are located at Kunming (25.6°N, 103.8°E), Sanya (18.4°N, 109.6°E), and Fuke (19.5°N, 109.1°E). The climatology and longitudinal variations in GW momentum fluxes and variance over the low-latitude region are reported. The GWs show strong seasonal variations and can greatly control the mesospheric horizontal winds via modulation of the quasi-geostrophic balance and momentum deposition. The different GW activities between Kunming and Sanya/Fuke are possibly consistent with the unique prevailing surface winds over Kunming and the convective system over the Tibetan Plateau according to the European Centre for Medium-Range Weather Forecasts (ECMWF), Reanalysis v5 (ERA5) data, and outgoing longwave radiation (OLR) data. These findings provide insight for better understanding the coupling between the troposphere and mesosphere. [ABSTRACT FROM AUTHOR]

In this study, we present nearly 9 years of the quasi16-day wave (Q16DW) in the mesosphere and lower thermosphere (MLT) wind at middle latitudes based on long-term wind observations between April 2014 and December 2022 by the Mengcheng (33.4°N, 116.5°E) meteor radar. There are two maxima in the Q16DW amplitude in the winter and early spring (near the equinox) and a minimum during the summer. The Q16DWs are relatively weak in meridional winds with no obvious seasonal variations. On average, the phase of the zonal Q16DW is larger than the meridional components with a mean difference that is slightly less than 90°, which suggests that there are orthogonal relationships between them. During the bursts of Q16DW, the periods in winter range between 15 and 18 d, whereas in summer, the periods of the planetary waves have a wider range. The wintertime Q16DW anomalies are, on average, amplified when the zonal wind shear anomalies increase, suggesting that barotropic instability may be a source of the Q16DW. Although the interannual variability of Q16DW amplitudes has been suggested observationally, there is no significant relationship between the interannual wind shear variability and Q16DW at most altitudes. [ABSTRACT FROM AUTHOR]

We present the migrating tidal winds decomposed jointly from multiple meteor radars in four longitudinal sectors situated in the equatorial mesosphere and lower thermosphere. The radars are located in Cariri, Brazil (7.4°S, 36.5°W), Kototabang, Indonesia (0.2°S, 100.3°E), Ascension Island, United Kingdom (7.9° S, 14.4° W), and Darwin, Australia (12.3°S, 130.8°E). Harmonic analysis was used to obtain amplitudes and phases for diurnal and semidiurnal solar migrating tides between 82 and 98 km altitude during the period 2005–2008. To verify the reliability of the tidal components calculated by the four meteor radar wind measurements, we also present a similar analysis for the Whole Atmosphere Community Climate Model winds, which suggests that the migrating tides are well observed by the four different radars. The tides include the important tidal components of diurnal westward‐propagating zonal wavenumber 1 and semidiurnal westward‐propagating zonal wavenumber 2. In addition, the results based on observations were compared with the Climatological Tidal Model of the Thermosphere (CTMT). In general, in terms of climatic features, our results for the major components of migrating tides are qualitatively consistent with the CTMT models derived from satellite data. In addition, the tidal amplitudes are unusually stronger in January–February 2006. This result is probably because tides were enhanced by the 2006 Northern Hemisphere stratospheric sudden warming event. Key Points: The diurnal and semidiurnal migrating tides are derived by multi‐meteor radars in the equatorial regionThe seasonal variations of diurnal westward‐propagating zonal wavenumber 1 (DW1) and semidiurnal westward‐propagating zonal wavenumber 2 (SW2) observations are similar to those tidal components in Climatological Tidal Model of the Thermosphere modelingThe unusual enhancements of DW1 and SW2 in February 2006 are possibly associated with the 2006 Northern Hemisphere stratospheric sudden warming event [ABSTRACT FROM AUTHOR]

The NCAR Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCM-X) v2.1 has been extended to include the neutral and ion–molecule chemistry and dynamics of three metals (Mg, Na, and Fe), which are injected into the upper mesosphere–lower thermosphere by meteoric ablation. Here we focus on the self-consistent electrodynamical transport of metallic ions in both the E and F regions. The model with full ion transport significantly improves the simulation of global distribution and seasonal variations of Mg+ , although the peak density is slightly lower (about 35 % lower in peak density) compared with the SCIAMACHY measurements. Near the magnetic equator, the diurnal variation in upward and downward transport of Mg+ is generally consistent with the "ionosphere fountain effect". The thermospheric distribution of Fe is shown to be closely coupled to the transport of Fe+. The effect of ion mass on ion transport is also examined: the lighter ions (Mg+ and Na+) are transported above 150 km more easily than the heavy Fe+. We also examine the impact of the transport of major molecular ions, NO+ and O2+ , on the distribution of metallic ions. [ABSTRACT FROM AUTHOR]

Long-lived metallic ions in the Earth's atmosphere (ionosphere) have been investigated for many decades. Although the seasonal variation in ionospheric "sporadic E " layers was first observed in the 1960s, the mechanism driving the variation remains a long-standing mystery. Here, we report a study of ionospheric irregularities using scintillation data from COSMIC satellites and identify a large-scale horizontal transport of long-lived metallic ions, combining the simulations of the Whole Atmosphere Community Climate Model with the chemistry of metals and ground-based observations from two meridional chains of stations from 1975–2016. We find that the lower thermospheric meridional circulation influences the meridional transport and seasonal variations of metallic ions within sporadic E layers. The winter-to-summer meridional velocity of ions is estimated to vary between -1.08 and 7.45 m/s at altitudes of 107–118 km between 10–60 ∘ N. Our results not only provide strong support for the lower thermospheric meridional circulation predicted by a whole atmosphere chemistry–climate model, but also emphasize the influences of this winter-to-summer circulation on the large-scale interhemispheric transport of composition in the thermosphere–ionosphere. [ABSTRACT FROM AUTHOR]

The application of inertial gravity wave parameterization has allowed for the spontaneous generation of quasi-biennial oscillation (QBO) in the Whole Atmosphere Community Climate Model (WACCM), although there is some mismatch when comparing with observations. The parameterization is based on Lindzen's linear saturation theory, modified to describe inertia-gravity waves (IGW) by considering the Coriolis effect. In this work, we improve the parameterization by importing a more realistic IGW phase speed spectrum that exhibits a double peak Gaussian distribution calculated from tropical radiosonde observations. A series of numeric simulations are performed to test the sensitivity of QBO-like oscillation features to the phase speed spectrum and the settings of parameterized IGW. All these simulations are capable of generating equatorial wind oscillations in the stratosphere based on standard spatial resolution settings. Central phase speeds of the 'double-Gaussian parameterization' affect QBO magnitudes and periods, and the momentum flux of IGW determines the acceleration rate of zonal wind. Furthermore, stronger IGW forcing can lead to a propagation of the QBO-like oscillation to lower altitude. The intermittency factor of the parameterization also prominently affects the QBO period. Stratospheric QBO-like oscillation with obvious improvements is generated using the new IGW parameterization in a long-time simulation. [ABSTRACT FROM AUTHOR]