Superposition of gravity waves with different propagation characteristics observed by airborne and space-borne infrared sounders

Abstract

Abstract. Many gravity wave analyses, based on either observations or model simulations, assume the presence of only a single dominant wave. This paper shows that there are much more complex cases with gravity waves from multiple sources crossing each others' paths. A complex gravity wave structure consisting of a superposition of multiple wave packets was observed above southern Scandinavia on 28 January 2016 with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA). The tomographic measurement capability of GLORIA enabled a detailed 3-D reconstruction of the gravity wave field and the identification of multiple wave packets with different horizontal and vertical scales. The larger-scale gravity waves with horizontal wavelengths of around 400 km could be characterised using a 3-D wave-decomposition method. The smaller-scale wave components with horizontal wavelengths below 200 km were discussed by visual inspection. For the larger-scale gravity wave components, a combination of gravity-wave ray-tracing calculations and ERA5 reanalysis fields identified orography as well as a jet-exit region and a low-pressure system as possible sources. All gravity waves are found to propagate upward into the middle stratosphere, but only the orographic waves stay directly above their source. The comparison with ERA5 also shows that ray tracing provides reasonable results even for such complex cases with multiple overlapping wave packets. Despite their coarser vertical resolution compared to GLORIA measurements, co-located AIRS measurements in the middle stratosphere are in good agreement with the ray tracing and ERA5 results, proving once more the validity of simple ray-tracing models. Thus, this paper demonstrates that the high-resolution GLORIA observations in combination with simple ray-tracing calculations can provide an important source of information for enhancing our understanding of gravity wave propagation.

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

“…The United Kingdom has preferential conditions for orographic GW generation, where surface winds have a long path over the oceans before encountering mountainous terrain (e.g., Bacmeister, 1993). Both these locations also lie under regions of significant variability in the latitudinal position of the upper tropospheric jet, which could result in increased measurement of nonorographic waves over these regions from spontaneous adjustment processes in the jet exit region (e.g., Bossert et al., 2020; Krisch et al., 2020; O'Sullivan & Dunkerton, 1995).…”

“…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., 2017, 2018, 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.…”

Atmospheric Gravity Waves in Aeolus Wind Lidar Observations

“…(2020), and Krisch et al. (2020), among others. The data here have been interpolated onto a regular grid in order to carry out the Savitzky‐Golay filtering, a process which itself will tend to smooth the peaks of each wave and reduce their amplitude.…”

On the occurrence of strong vertical wind shear in the tropopause region: a 10-year ERA5 northern hemispheric study

“…7c) is associated with the TEJ. These easterlies generally arise from June to September as part of the EASM circulation at upper-tropospheric pressure levels around 150 hPa (Krishnamurti and Bhalme, 1976). Fig.…”