Lidar-observed temperature structures and gravity-wave perturbations of the mesopause region in the springs of 1990–1992 over Fort Collins, CO

Abstract

The Na temperature lidar data taken during the nine nights in springs 1990 and 1991 at Fort Collins, CO, have been re-analyzed by a refined procedure, which takes into account the effects of (i) the more accurately determined lidar operational frequencies, (ii) the proper inclusion of extinction in the Na layer and (iii) additional temporal and spatial smoothing. Depending on altitudes, the new lidar frequencies and the effect of Na extinction combined to lower the calculated temperature values by 2–8 K. Although the occasionally noted large rapid change (in 15 min) in the centroid temperature is reduced from ∼40 K to ∼20 K due to the added smoothing first employed by Bills and Gardner, the general conclusion presented in the recently published paper [1] remains valid. In this paper, we also present the analysis of new data (a total of 17 nights) taken during spring 1992 which further substantiates the fact that the averaged mesopause in spring rises from a lower altitude before midnight to a higher altitude after midnight. In addition, parameters depicting atmospheric gravity-wave perturbations have been derived from the measured temperature profiles. Using the data collected in 26 spring nights, we have determined the averaged relative density (temperature) perturbation, Brunt Vaisala period and Richardson number to be, respectively, 5.1±1.1%, 5.1±0.3 min, and 1.8±1.0.