Three-dimensional tomographic reconstruction of atmospheric gravity waves in the mesosphere and lower thermosphere (MLT)
Abstract. Gravity waves (GWs) have been intensively studied over recent decades because
of their dominant role in the dynamics of the mesosphere and lower
thermosphere (MLT). The momentum deposition caused by breaking GWs determines
the basic structure and drives the large-scale circulation in the MLT.
Satellite observations provide a way to qualify the properties and effects of
GWs on a global scale. As GWs can propagate vertically and horizontally in
the atmosphere, resolving both horizontal and vertical wavelengths is
important for the quantification of a wave. However, this can hardly be
achieved by one instrument with a good spatial coverage and resolution. In
this paper, we propose a new observation strategy, called “sweep mode”, for
a real three-dimensional (3-D) tomographic reconstruction of GWs in the MLT
by modifying the observation geometry of conventional limb sounding
measurements. It enhances the horizontal resolution that typical limb
sounders can achieve, while at the same time retaining the good vertical
resolution they have. This observation strategy is simulated for retrieving
temperatures from measurements of the rotational structure of the O2 
A-band airglow. The idea of this observation strategy is to sweep the
line of sight (LOS) of the limb sounder horizontally across the orbital track
during the flight. Therefore, two-dimensional (2-D) slices, i.e., vertical
planes, that reveal the projection of GWs can be observed in the direction
along and across the orbital track, respectively. The 3-D wave vector is
then reproduced by combining the projected 2-D wave slices in the two
directions. The feasibility of this sweep-mode tomographic retrieval
approach is assessed using simulated measurements. It shows that the
horizontal resolution in both along- and across-track directions is affected
by an adjustable turning angle, which also determines the spatial coverage of
this observation mode. The retrieval results can reduce the errors in
deducing momentum flux substantially by providing an unbiased estimation of
the real horizontal wavelength of a wave.