Rayleigh-Lidar Observations of Mesospheric Mid-latitude Density Climatology above Utah State University

Data from Rayleigh lidars have been used extensively to derive temperatures in the mesospheric region of the atmosphere. However, these data have not been used extensively in a similar way to derive neutral densities. We report on one such mid-latitude, density climatology between 45 and ~90 km, based on nearly 600 good nights of observations carried out since 1993 at the Atmospheric Lidar Observatory (ALO) at Utah State University (41.7°N 111.8°W). They produce relative density profiles that are then normalized at 45 km to an empirical model, in this case the MSISe00 model. Despite this normalization, significant differences are found between the observations and the model starting as low as 50 km. For instance, the lower mesosphere is denser than the model in summer and less dense in winter. In contrast, the upper mesosphere is denser near the equinoxes and less dense at other times. Differences between the climatology and the model reach ±11%. The normalized observations show a large seasonal variation, with the summer densities in the 65-75 km region being approximately 55% greater than the winter densities. At both lower and higher altitudes, the seasonal variation is less.