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. Gravity waves (GWs) have been intensively studied over recent decades becauseof their dominant role in the dynamics of the mesosphere and lowerthermosphere (MLT). The momentum deposition caused by breaking GWs determinesthe basic structure and drives the large-scale circulation in the MLT.Satellite observations provide a way to qualify the properties and effects ofGWs on a global scale. As GWs can propagate vertically and horizontally inthe atmosphere, resolving both horizontal and vertical wavelengths isimportant for the quantification of a wave. However, this can hardly beachieved by one instrument with a good spatial coverage and resolution. Inthis paper, we propose a new observation strategy, called “sweep mode”, fora real three-dimensional (3-D) tomographic reconstruction of GWs in the MLTby modifying the observation geometry of conventional limb soundingmeasurements. It enhances the horizontal resolution that typical limbsounders can achieve, while at the same time retaining the good verticalresolution they have. This observation strategy is simulated for retrievingtemperatures from measurements of the rotational structure of the O2 A-band airglow. The idea of this observation strategy is to sweep theline of sight (LOS) of the limb sounder horizontally across the orbital trackduring the flight. Therefore, two-dimensional (2-D) slices, i.e., verticalplanes, that reveal the projection of GWs can be observed in the directionalong and across the orbital track, respectively. The 3-D wave vector isthen reproduced by combining the projected 2-D wave slices in the twodirections. The feasibility of this sweep-mode tomographic retrievalapproach is assessed using simulated measurements. It shows that thehorizontal resolution in both along- and across-track directions is affectedby an adjustable turning angle, which also determines the spatial coverage ofthis observation mode. The retrieval results can reduce the errors indeducing momentum flux substantially by providing an unbiased estimation ofthe real horizontal wavelength of a wave.

Three-dimensional tomographic reconstruction of atmospheric gravity waves in the mesosphere and lower thermosphere (MLT)