Abstract
Abstract. Three-dimensional measurements of gravity waves are required in order to quantify their direction-resolved momentum fluxes and obtain a better understanding of their propagation characteristics. Such 3-D measurements of gravity waves in the lowermost stratosphere have been provided by the airborne Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) using full angle tomography. Closed flight patterns of sufficient size are needed to acquire the full set of angular measurements for full angle tomography. These take about 2 h and are not feasible everywhere due to scientific reasons or air traffic control restrictions. Hence, this paper investigates the usability of limited angle tomography for gravity wave research based on synthetic observations. Limited angle tomography uses only a limited set of angles for tomographic reconstruction and can be applied to linear flight patterns. A synthetic end-to-end simulation has been performed to investigate the sensitivity of limited angle tomography to gravity waves with different wavelengths and orientations with respect to the flight path. For waves with wavefronts roughly perpendicular to the flight path, limited angle tomography and full angle tomography can derive wave parameters like wavelength, amplitude, and wave orientation with similar accuracy. For waves with a horizontal wavelength above 200 km and vertical wavelength above 3 km, the wavelengths can be retrieved with less than 10 % error, the amplitude with less than 20 % error, and the horizontal wave direction with an error below 10∘. This is confirmed by a comparison of results obtained from full angle tomography and limited angle tomography for real measurements taken on 25 January 2016 over Iceland. The reproduction quality of gravity wave parameters with limited angle tomography, however, depends strongly on the orientation of the waves with respect to the flight path. Thus, full angle tomography might be preferable in cases in which the orientation of the wave cannot be predicted or waves with different orientations exist in the same volume and thus the flight path cannot be adjusted accordingly. Also, for low-amplitude waves and short-scale waves full angle tomography has advantages due to its slightly higher resolution and accuracy.
Highlights
Gravity waves (GWs) couple the atmosphere vertically by transporting energy and momentum from the surface to altitudes as far as the mesosphere. On this path through the atmosphere, GWs interact with the mean flow and, are responsible for the wind reversal in the mesosphere and influence prominent circulation patterns such as the quasibiennial oscillation (QBO) of stratospheric tropical winds and the meridional Brewer–Dobson circulation (BDC) in the stratosphere
Former studies demonstrated the feasibility of 2-D tomography of rearward-looking satellite instruments for the retrieval of 3-D atmospheric structures such as GWs (Degenstein et al, 2004; Ungermann et al, 2010a; Hultgren et al, 2013)
In 2-D tomography a volume is reconstructed from rearwardlooking measurements on a moving platform that slice the volume into multiple 2-D images
Summary
Gravity waves (GWs) couple the atmosphere vertically by transporting energy and momentum from the surface to altitudes as far as the mesosphere On this path through the atmosphere, GWs interact with the mean flow and, are responsible for the wind reversal in the mesosphere and influence prominent circulation patterns such as the quasibiennial oscillation (QBO) of stratospheric tropical winds and the meridional Brewer–Dobson circulation (BDC) in the stratosphere. Retrieved wave parameters a wave with a wave direction of 0◦ has east–west oriented wavefronts and is tilted towards the north, a wave with a wave direction of 180◦ is tilted towards the south These synthetic waves are added to the climatological temperature field to gain the synthetic temperature field T s ∈ Rm. These synthetic waves are added to the climatological temperature field to gain the synthetic temperature field T s ∈ Rm From this predetermined atmospheric state and with a given flight path, the GLORIA measurement simulator The background removal subtracts this temperature field T c from the retrieved temperature field T r and the temperature residual or so-called retrieved wave field wr remains
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