Climatology and long-term trends in middle atmospheric temperatures at mid-latitudes observed by the Rayleigh/Sodium Lidar over Hefei, China (32° N, 117° E)

In this study, the climatology and long-term trends of middle atmospheric temperatures at mid-latitudes are investigated using Rayleigh/Sodium lidar observations collected from January 2010 to December 2021 over Hefei, China (32°N, 117°E). The seasonal variations and vertical profiles of lidar-derived temperatures demonstrate strong agreement with temperature measurements from the Microwave Limb Sounder (MLS) instrument on the Earth Observing System (EOS) Aura satellite. In terms of seasonal variation, middle atmospheric temperatures primarily exhibit annual oscillations (AO) and semi-annual oscillations (SAO). Harmonic analysis of the lidar and MLS temperature data reveals close phase alignment for both AO and SAO, with AO amplitudes ranging from 2 to 6 K and SAO amplitudes from 1 to 4 K. The dependence of temperature on solar forcing was analyzed using the F10.7 index as a proxy, showing positive solar response coefficients at all altitudes, with a maximum of 15 ± 1.1 K/100 SFU observed near 42–44 km. After removing the temperature response to solar cycle variations, a cooling trend in mid-latitude temperatures is evident across all altitudes, ranging from 3 to 6 K/decade.