EPP

A meteor radar chain located along the 120°E meridian in the Northern Hemisphere from low to middle latitudes provides long-term horizontal wind observations of the mesosphere and lower thermosphere (MLT) region. In this study, we report a seasonal variation and its latitudinal feature in the horizontal mean wind in the MLT region observed by six meteor radar instruments located at Mohe (53.5°N, 122.3°E), Beijing (40.3°N, 116.2°E), Mengcheng (33.4°N, 116.5°E), Wuhan (30.6°N, 114.4°E), Kunming (25.6°N, 108.3°E), and Fuke (19.5°N, 109.1°E) stations. In addition, we compare the wind in the MLT region measured by the meteor radar stations with those simulated by the Whole Atmosphere Community Climate Model (WACCM). In general, the WACCM appears to capture well the seasonal and latitudinal variations in the zonal wind component. In particular, the temporal evolution of the eastward zonal wind maximum shifts from July to May as the latitude decreases. However, the simulated WACCM meridional wind exhibits differences from the meteor radar observations.

Observations of a quasi-90-day oscillation in the mesosphere and lower thermosphere (MLT) region from April 2011 to December 2014 are presented in this study. There is clear evidence of a quasi-90-day oscillation in temperatures obtained from the Kunming meteor radar (25.6°N, 103.8°E) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), as well as in wind observed by the Kunming meteor radar. The quasi-90-day oscillation appears to be a prominent feature in the temperatures and meridional wind tides and presents quite regular cycles that occur approximately twice per year. The amplitudes and phases of the quasi-90-day oscillation in the SABER temperature show a feature similar to that of upward-propagated diurnal tides, which have a vertical wavelength of ~20 km above 70 km. In the lower atmosphere, a similar 90-day variability is presented in the surface latent heat flux and correlates with the temperature in the MLT region. Similar to the quasi-90-day oscillation in temperature, a 90-day variability of ozone (O₃) is also present in the MLT region and is considered to be driven by a similar variability in the upwardly-propagated diurnal tides generated in the lower atmosphere. Moreover, the 90-day variability in the absorption of ultraviolet (UV) radiation by daytime O₃ in the MLT region is an in situ source of the quasi-90-day oscillation in the MLT temperature.