Horizontal Wavenumber Spectra Across the Middle Atmosphere From Airborne Lidar Observations During the 2019 Southern Hemispheric SSW

• Published in: Geophysical Research Letters
• Main Authors: Knobloch, Stefanie, Kaifler, Bernd, Dörnbrack, Andreas, Rapp, Markus
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: ddc:551.5; gravity waves; middle atmosphere; airborne lidar; horizontal wavenumber spectrum; SSW; Antarc*; Antarctic; Antarctic Peninsula; Drake Passage
• Online Access: https://doi.org/10.1029/2023GL104357; http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/11684

Abstract Horizontal wavenumber spectra across the middle atmosphere are investigated based on density measurements with the Airborne Lidar for Middle Atmosphere research (ALIMA) in the vicinity of the Southern Andes, the Drake passage and the Antarctic peninsula in September 2019. The probed horizontal scales range from 2000 to 25 km. Spectral slopes are close to k −5/3 in the stratosphere and get shallower for horizontal wavelengths <200 km in the mesosphere. The spectral slopes are shown to be statistically robust with the presented number of flight legs despite the unknown orientation of true wave vectors relative to the flight track using synthetic data and a Monte Carlo approach. The largest spectral amplitudes are found over the ocean rather than over topography. The 2019 sudden stratospheric warming caused a critical level for MWs and a reduction of spectral amplitudes at horizontal wavelengths of about 200 km in the mesosphere. Plain Language Summary: The spectral analysis of observations along extended flight tracks helps to determine the contribution of different length scales to atmospheric processes. In this study we calculate horizontal wavenumber spectra in the altitude range between 20 and 80 km, the middle atmosphere, based on observations from the Airborne Lidar for Middle Atmosphere research onboard the HALO aircraft. The observations were performed in the vicinity of the Southern Andes, the Drake passage and the Antarctic peninsula during September 2019. The observed horizontal scales range from 2000 km to about 25 km and cover almost the entire mesoscale range of atmospheric dynamics in the middle atmosphere. This study finds that vertical oscillations in the atmosphere, called gravity waves, cause the slopes and power of the spectra at the observed horizontal scales in the middle atmosphere. The slopes and power of the horizontal spectra vary with varying gravity wave activity during the period of observations. Key Points: Horizontal wavenumber spectra across the middle atmosphere are ...