Orographically induced spontaneous imbalance within the jet causing a large-scale gravity wave event

• Published in: Atmospheric Chemistry and Physics
• Main Authors: M. Geldenhuys, P. Preusse, I. Krisch, C. Zülicke, J. Ungermann, M. Ern, F. Friedl-Vallon, M. Riese
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Greenland
• Online Access: https://doi.org/10.5194/acp-21-10393-2021; https://doaj.org/article/6fdeae9688f7435d9833bef25fca6c1c

To better understand the impact of gravity waves (GWs) on the middle atmosphere in the current and future climate, it is essential to understand their excitation mechanisms and to quantify their basic properties. Here a new process for GW excitation by orography–jet interaction is discussed. In a case study, we identify the source of a GW observed over Greenland on 10 March 2016 during the POLSTRACC (POLar STRAtosphere in a Changing Climate) aircraft campaign. Measurements were taken with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) instrument deployed on the High Altitude Long Range (HALO) German research aircraft. The measured infrared limb radiances are converted into a 3D observational temperature field through the use of inverse modelling and limited-angle tomography. We observe GWs along a transect through Greenland where the GW packet covers ≈ <math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">1</mn><mo>/</mo><mn mathvariant="normal">3</mn></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="20pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="dad779fc4d6ec81af5f2e51c87dd9156"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-10393-2021-ie00001.svg" width="20pt" height="14pt" src="acp-21-10393-2021-ie00001.png"/></svg:svg> of the Greenland mainland. GLORIA observations indicate GWs between 10 and 13 km of altitude with a horizontal wavelength of 330 km , a vertical wavelength of 2 km and a large temperature amplitude of 4.5 K . Slanted phase fronts indicate intrinsic propagation against the wind, while the ground-based propagation is with the wind. The GWs are arrested below a critical layer above the tropospheric jet. Compared to its intrinsic horizontal group velocity (25–72 m s −1 ) the GW packet has a slow vertical group velocity of 0.05–0.2 m s −1 . ...