Limited angle tomography of mesoscale gravity waves by the infrared limb-sounder GLORIA

Abstract

Abstract. Three-dimensional measurements of gravity waves are required in order to quantify their directionresolved 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-toend 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.

An 18‐Year Climatology of Directional Stratospheric Gravity Wave Momentum Flux From 3‐D Satellite Observations

“…To fully constrain their directional GWMF, 3-D observations are needed. Three-dimensional stratospheric measurements are notoriously challenging and are normally limited to specialist instrumentation (Ern et al, 2004;Krisch et al, 2017Krisch et al, , 2018Krisch et al, , 2020. Combinations of instruments (e.g., Alexander, 2015;Faber et al, 2013;Wright et al, 2016), or the use of supplementary wind information (e.g., Alexander & Barnet, 2007;Alexander et al, 2009), have been used to infer 3-D GW structure, but these require limiting assumptions and are confined to colocated and/or coincident measurements.…”

The MATS satellite mission – gravity wave studies by Mesospheric Airglow/Aerosol Tomography and Spectroscopy

“…An important basis for MATS is the InnoSat satellite platform developed by OHB Sweden and ÅAC Microtec (Larsson et al, 2016). InnoSat has been designed as a "universal" microsatellite platform that can host a variety of different payloads for aeronomy or astronomy research in low-Earth orbit.…”

3-D tomographic limb sounder retrieval techniques: irregular grids and Laplacian regularisation

“…In order to implement this technique, one needs a way to generate a random vector x with the required covariance, represented by a known, symmetric, positive definite covariance matrix S a . This can be done by generating a vector u of independent standard normal random variables and finding a square matrix L such that L L T = S a (Kroese et al, 2013). Then we can set x = Lu, and…”