We present a first analysis of 9 and 6.75 day periodic oscillations observed in the neutral mesospheric density in 2005 and 2006. Mesospheric densities near 90 km are derived using data from the Davis meteor radar (68.5°S, 77.9°E; magnetic latitude, 74.6°S), Antarctica. Spectral analysis indicates that the pronounced periodicities of 9 and 6.75 days observed in the mesosphere densities are associated with variations in solar wind high‐speed streams and recurrent geomagnetic activity. Neutral mesospheric winds and temperatures, simultaneously measured by the Davis meteor radar, also exhibit 9 and 6.75 day periodicities. A Morlet wavelet analysis shows that the time evolution of the 9 and 6.75 day oscillations in the neutral mesosphere densities and winds are similar to those in the solar wind and in planetary magnetic activity index, Kp in 2005 and 2006. These results demonstrate a direct coupling between Sun's corona (upper atmosphere) and the Earth's mesosphere.

We report an analysis of the neutral mesosphere density response to geomagnetic activity from January 2016 to February 2017 over Antarctica. Neutral mesospheric densities from 85 to 95 km are derived using data from the Davis meteor radar (68.5°S, 77.9°E) and the Microwave Limb Sounder on the Aura satellite. Spectral and Morlet wavelet analyses indicate that a prominent oscillation with a periodicity of 13.5 days is observed in the mesospheric density during the declining phase of solar cycle 24 and is associated with variations in solar wind high‐speed streams and recurrent geomagnetic activity. The periodic oscillation in density shows a strong anticorrelation with periodic changes in the auroral electrojet index. These results indicate that a significant decrease in neutral mesospheric density as the geomagnetic activity enhances.

In this study, mesopause temperatures over a low‐latitude station were derived by applying the temperature gradient model technique to data from a meteor radar installation located in Kunming (25.6°N, 103.8°E), China. The estimated temperatures are in good agreement with Sounding of the Atmosphere by Broadband Emission Radiometry (SABER) temperatures and exhibit clear seasonal and interannual variations with dominant spectral peaks at annual, semiannual, quasi 90 day, and terannual oscillations. However, the amplitudes of the temperature fluctuations and the dominant spectral peaks are larger than those from SABER. An improved method that accounts for the temperature sensitivity of the slope estimated from the meteor radar data was developed to calibrate the larger fluctuations obtained using the temperature gradient model technique. The resulting calibrated temperatures are more consistent with SABER observations, and the accuracy of the derived temperatures is significantly improved.