The seasonal variations in gravity wave (GW) vertical fluxes of zonal momentum and heat in the mesopause region are calculated using nearly 10 years (from 2012 to 2021) of temperature and wind observations by a narrowband sodium lidar located in Hefei, China (32°N, 117°E). Except in summer, the GW zonal momentum fluxes are mostly westward, with ∼80% contributed by the short‐period (10 min–1 hr) GWs, and anticorrelate with the eastward zonal wind. The mean westward zonal momentum fluxes in spring and winter are −2.55 and −1.78 m²/s², respectively, which are much stronger than −0.98 m²/s² in fall. The momentum flux in summer is primarily eastward, dominated by long‐period (1–16 hr) GWs. These seasonal variations in zonal momentum fluxes are mainly due to the filtering of GWs by the mean background wind at lower altitudes. The annual mean zonal momentum flux is westward with a value of −1.08 m²/s². The calculated acceleration from flux divergence is westward below 93 km, opposite to the eastward mean zonal wind. The heat flux below 94 km is downward throughout the year, with no apparent seasonal variation. The annual mean heat flux is primarily downward, with a cooling rate of ∼−35 K/day between 87 and 95 km.

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.

A strong Southern Hemisphere (SH) sudden stratospheric warming event occurred in September 2019 and significantly weakened the stratospheric polar vortex. Due to the positive zonal wind anomalies in the troposphere, the barotropic/baroclinic instability, primarily controlled by the horizontal/vertical wind shear, weakened in the upper troposphere at midlatitudes in late September and early October. As a result, planetary waves (PWs) were deflected equatorward near the tropopause rather than upward into the stratosphere, resulting in less perturbation to the stratospheric polar vortex. After October 15, the westward zonal wind anomalies propagate downward and reach the troposphere, increasing the tropospheric barotropic/baroclinic instability. This benefits the propagation of PWs into the stratosphere, leading to the early breaking of the stratospheric polar vortex. In turn, the SH mesosphere becomes anomalously cold due to the stratospheric wind filtering on the gravity waves, leading to the much earlier onset of SH polar mesospheric clouds.

The Venus atmosphere Superrotation (SR) is successfully simulated with the high‐resolution (1.25° × 1.25° in longitude and latitude) runs of the Venus Planetary Climate Model (PCM). The results show a clear spectrum and structure of atmospheric waves, primarily with periods of 5.65 and 8.5 days. The simulation reproduces long‐term quasi‐periodic oscillation of the zonal wind and primary planetary‐scale wave seen in observations. These oscillations occur with a period of 163–222 days, although their existence is still debated in observations. The Rossby waves show similarity in wave characteristics and angular momentum (AM) transport due to Rossby‐Kelvin instability by comparing the 5.65‐day wave in Venus PCM with the 5.8‐day wave simulated by AFES‐Venus, another Venus General Circulation Model. Similarities are also evident between the 8.5‐day wave in Venus PCM and the 7‐day wave obtained in AFES‐Venus. The long‐term variations in the AM budget indicate that the 5.65‐day wave is the dominant factor of the oscillation on the SR, and the 8.5‐day wave plays a secondary role. When the 5.65‐day wave grows, its AM and heat transport are enhanced and accelerate (decelerate) the lower‐cloud equatorial jet (cloud‐top mid‐latitude jets). Meanwhile, the 8.5‐day wave weakens, reducing its deceleration effect on the lower‐cloud equator. This further suppresses the meridional gradient of the background wind and weakens instability, leading to the decay of the 5.65‐day wave. And vice versa when the 5.65‐day wave decays.

Planetary waves play an essential role in the momentum budget of Venus's atmosphere superrotation. Using the Longwave Infrared Camera (LIR) observations of the Akatsuki and their cloud‐tracking wind fields, we study the characteristics of planetary waves and their long‐term variations. The dominant planetary wave is a wavenumber 1 wave with a period of 5–6 days (Quasi‐Five‐Day wave or QFDW) and is symmetrically distributed in the midlatitudes of both hemispheres. The wave phase speed is close to the background zonal wind, indicating the possible existence of a critical level near the LIR emission altitude of 65 km. The QFDW tends to appear at ∼8:00 a.m. local time, suggesting a modulation by the thermal tide. The QFDW amplitude is correlated with the vertical shear of the background zonal wind modulated by the thermal tide. This indicates some nonlinear interaction between the thermal tide and the QFDW.