3D reconstruction of atmospheric gravity waves and derivation of vertical wave parameters with tomography applied to data from two ground-based cameras observing OH airglow

Atmospheric gravity waves transport energy and momentum through the atmosphere and can travel large horizontal and vertical distances from the troposphere to the mesosphere and higher. They contribute to atmospheric dynamics and among others drive the meridional pole-to-pole circulation in the mesosphere. Thus, knowing about gravity waves, their spatio-temporal characteristics, their interaction with other waves and the atmospheric background is attracting more and more attention in order to further improve climate and even meteorological models.

In the upper mesosphere / lower thermosphere (UMLT) region around an altitude of 80km to 100km, OH airglow can be utilized for passive remote sensing and continuous nightly observations of atmospheric dynamics, especially of gravity waves. The OH airglow layer is a chemiluminescent layer with a strong emission in the short wave infrared spectral range (at about 1500nm) and is located at an altitude of about 86-87km with a layer halfwidth of about 4km. The OH airglow intensity is modulated by traversing atmospheric gravity waves which lead amongst others to a vertical transport of atomic oxygen. Observing the OH airglow with short-wave infrared imagers allows characterizing gravity waves. From these observations the horizontal wave parameters (horizontal wavelength, horizontal direction of propagation, etc.) can be derived.

In this study we present measurements of two ground-based FAIM (Fast Airglow IMager) systems, which are cameras sensitive in the short-wave infrared region observing the OH airglow layer with a high temporal resolution. The cameras are located at Oberpfaffenhofen, Germany and Otlica, Slovenia, about 300km apart from each other and are pointing to the same volume at about 87km located in the Alpine Region above Northern Italy. We developed a novel tomographic algorithm to allow for a three-dimensional reconstruction of the airglow layer by combining images from the two viewing angles. In order to solve the highly underdetermined equation system, prior knowledge of the OH airglow layer vertical profile is needed e.g. from multi-year observations of SABER on the TIMED satellite on a statistical basis, or Gaussian and Chapman basis functions. This allows us, among others, to derive the vertical wavelength of the waves, their three-dimensional propagation direction, and their three-dimensional structure. From that knowledge, further wave parameters but also the horizontal wind along the wave propagation can be estimated via the wave’s dispersion relation.

We will explain the tomographic reconstruction method, its capabilities and limits and will present a detailed case study showing a 3D-reconstructed gravity wave and the derivation of its parameters.

This work received funding from the Bavarian State Ministry of the Environment and Consumer Protection.