Investigation on Spectral Characteristics of Gravity Waves in the MLT Using Lidar Observations at Andes

Abstract Based on observations from lidar at Andes, we study the features of gravity wave activities and their spectra in the mesosphere and lower thermosphere (MLT). Case analysis shows that a quasi‐monochromatic inertia–gravity wave (IGW) dominates the perturbation fields, with clearly downward phase progression in the wind and temperature fields. Statistical investigation shows that the dominant waves in the MLT over Andes have the typical temporal and spatial scales of IGWs and show the preferential propagation in the meridional direction relative to in the zonal direction. The preferential propagation direction causes larger spectral peak and steeper spectral slope in the meridional wind as compared to the zonal counterpart. The 27‐night observations indicate that the frequency (vertical wavenumber) spectrum has the slopes of about −1.4 (−1.5), −1.7 (−2.0), and −2.3 (−2.6) in the zonal wind, meridional wind, and relative temperature perturbations, more or less deviated from the universal spectral index of −5/3 (−3), respectively. The vertical wind has a steeper spectral tail in both the frequency and wavenumber spectra, which is different from the other three components. In the saturated spectrum region, the frequency and vertical wavenumber spectra have the slopes of −0.4 and −1.1 in the vertical wind, which are much shallower than those in the zonal and meridional winds, respectively. In the spectral tail region, the frequency and wavenumber spectrum slopes of −2.2 and −3.5 are far steeper relative to their saturated spectrum slopes. This suggests that the vertical wind should obey the different spectral laws from the horizontal winds.