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Airborne measurements and large-eddy simulations of small-scale Gravity Waves at the tropopause inversion layer over Scandinavia.

Airborne measurements and large-eddy simulations of small-scale Gravity Waves at the tropopause inversion layer over Scandinavia.

Authors :
Gisinger, Sonja
Wagner, Johannes
Witschas, Benjamin
Source :
Atmospheric Chemistry & Physics Discussions; 4/9/2020, p1-33, 33p
Publication Year :
2020

Abstract

Coordinated airborne measurements were performed by the two research aircraft DLR Falcon and HALO (High Altitude and Long Range Aircraft) in Scandinavia during the GW-LCYCLE~II (Investigation of the life cycle of gravity waves) campaign in 2016 to investigate gravity wave processes in the upper troposphere and lower stratosphere (UTLS) region. A mountain wave event was probed over Southern Scandinavia on 28 January 2016. The collected dataset constitutes a valuable combination of in-situ measurements and horizontal- and altitude-resolved wind lidar and water vapour lidar measurements. In-situ data at different flight altitudes and downward pointing Doppler wind lidar measurements show pronounced changes of the horizontal scales in the vertical velocity field and of the leg-averaged momentum fluxes (MF) in the UTLS region. The vertical velocity field was dominated by small horizontal scales with a decrease from around 20 km to < 10 km in the vicinity of the tropopause inversion layer (TIL). These small scales were also found in the water vapour and reflectivity data. The MF profile downstream of the main mountain ridge determined from the wind lidar data is characterized by negative fluxes below and positive fluxes above the TIL which show similar magnitudes. The combination of the observations and idealized large-eddy simulations (LES) revealed the occurrence of interfacial waves on the tropopause inversion during the MW event. Such interfacial waves have already been observed on boundary-layer inversions but their concept has not been applied to tropopause inversions so far. Our idealized simulations revealed that interfacial waves can occur also on tropopause inversions and our analyses of the horizontal- and altitude-resolved airborne observations revealed that they actually do. As predicted by linear theory, the horizontal scale of those waves is determined by the wind and stability conditions above the inversion. They are found downstream of the main mountain peaks and their characteristic MF profile clearly distinguishes from the MF profile of a Kelvin-Helmholtz instability. Further, the idealized large-eddy simulations revealed that the presence of the TIL is crucial in producing this kind of trapped waves at tropopause altitude. mountainous regions. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
16807367
Database :
Complementary Index
Journal :
Atmospheric Chemistry & Physics Discussions
Publication Type :
Academic Journal
Accession number :
142650993
Full Text :
https://doi.org/10.5194/acp-2020-121