Search for: All records

We present midlatitude solar response and linear trend from Colorado State University/Utah State University Na lidar nocturnal temperature observations between 1990 and 2017. Along with the nightly mean temperatures (_Ngt), we also use the corresponding 2‐hr means centered at midnight (_2MN), resulting in vertical trend profiles similar in shapes as those previously published. The 28‐year trend from _Ngt (_2MN) data set starts from a small warming at 85 km, to cooling at 87 (88) km, reaching a maximum of 1.85 ± 0.53 (1.09 ± 0.74) at 92 (93) km and turns positive again at 102 (100) km. The 6‐month winter trend is much cooler than the 4‐month summer trend with comparable solar response varying around 5 ± 1 K/100 SFU throughout the profile (85–105 km) with higher summer values. We explore the observed summer/winter trend difference in terms of observed gravity wave heat flux heating rate at a nearby station and the long‐term trend of gravity wave variance at a midlatitude. Between 89 and 100 km, the lidar trends are within the error bars of the Leibniz Middle Atmosphere (LIMA) summer trends (1979–2013), which are nearly identical to the lidar‐Ngt trend. We address the need of long data set for reliable analysis on trend, the extent of trend uncertainty due to possible tidal bias, the effect of a Pinatubo/episodic function, and the impact of stratospheric ozone recovery.

Abstract. Lidar observations of the mesospheric Na layer have revealed considerablediurnal variations, particularly on the bottom side of the layer, where morethan an order-of-magnitude increase in Na density has been observed below 80 kmafter sunrise. In this paper, multi-year Na lidar observations areutilized over a full diurnal cycle at Utah State University (USU) (41.8^∘ N,111.8^∘ W) and a global atmospheric model of Na with 0.5 kmvertical resolution in the mesosphere and lower thermosphere (WACCM-Na) to explorethe dramatic changes of Na density on the bottom side of the layer. Photolysis of the principal reservoir NaHCO₃ is shown to beprimarily responsible for the increase in Na after sunrise, amplified by theincreased rate of reaction of NaHCO₃ with atomic H, which is mainlyproduced from the photolysis of H₂O and the reaction of OH withO₃. This finding is further supported by Na lidar observation at USUduring the solar eclipse (>96 % totality) event on 21 August 2017, when a decrease and recovery of the Na density on thebottom side of the layer were observed. Lastly, the model simulation showsthat the Fe density below around 80 km increases more strongly and earlierthan observed Na changes during sunrise because of the considerably fasterphotolysis rate of its major reservoir of FeOH.