A global view of stratopause gravity waves derived from CIPS RAA data

Gravity waves (GWs) near the stratopause can cause atmospheric density and/or ozone fluctuations. The Cloud Imaging and Particle Size (CIPS) instrument aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite is a nadir-viewing imager that measures scattered ultraviolet radiation at 265 nm. It is sensitive to small fluctuations in Rayleigh albedo driven by GWs with vertical wavelengths longer than 15 km and horizontal wavelengths of 15–600 km at altitudes of 50–55 km. These fluctuations can be quantified by the Rayleigh Albedo Anomaly (RAA); i.e., the residual difference between the observed Rayleigh scattering albedo and a “baseline” albedo that would be observed in the absence of any small-scale atmospheric perturbations. The CIPS RAA observations occupy a unique spatial and temporal niche in providing information about the vertical propagation of GWs from the lower atmosphere into the mesosphere. In order to facilitate quantitative analyses using CIPS RAA data and to reduce the random noise in the CIPS scenes, we have developed a variance data product that uses a Fast Fourier Transform (FFT) window filter. The RAA variances provide a quantitative measure of wave-driven fluctuations that can be used in automated analyses targeting GWs. In this paper, we describe the variance data and a climatological study of global observations of GWs near 50–55 km.