Comparison of Rayleigh-Scatter Lidar Temperature Climatologies in the Mesosphere and Lower Thermosphere Between the Traditional Reduction Method and the New Optimal Estimation Method

Virtual

An optimal estimation method (OEM) was used to obtain all-night temperature profiles from Rayleigh-scatter lidar (RSL) observations obtained by the original and updated lidar systems at Utah State University (USU). These data were used to produce annual climatologies of temperatures above USU. The climatology of temperatures from the original lidar, which operated from late 1993 through 2004, was compared with the climatology produced using the widely used Hauchecorne-Chanin method (HC). This comparison highlights the similarities at lower altitudes and differences, which start between 70 km and 80 km and extend to the top altitudes with the OEM temperatures warmer on average than those of the HC. The differences between methods are likely due to the reliance of the HC on a seeding temperature at the top altitude which likely has a large influence on the temperatures at the top 10 km. OEM and HC temperature climatologies were also produced using observations from the upgraded RSL at USU, which operated from early 2014 to early 2015. Like the original climatology, the newer climatology was seen to differ most at higher altitudes. The OEM climatologies from the original and newer data sets were compared, showing good agreement in the location of the summer mesopause but with colder temperatures in this region from the newer observations.