Propagation of mesoscale gravity waves in the atmosphere - a study based on airborne and spaceborne temperature observations

Gravity waves (GWs) are one of the most important coupling mechanisms in the atmosphere. They couple different compartments of the atmosphere. Within the GW-LCYCLE (Gravity Wave Life Cycle) project, an aircraft campaign has been performed in winter 2015/2016 to study the propagation of gravity waves. During this campaign, the first 3D tomographic measurements of GWs were taken with the infrared limb imager GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere).

Temperature distributions measured by GLORIA in the UTLS during strong GW events in January 2016 over Iceland and Southern Scandinavia will be presented. The 3-D nature of the GLORIA measurements allows for the determination of 3-D wave vectors, including the horizontal directions. These 3-D wave vectors enable the use of the linear ray-tracing. Many studies use linear ray-tracing to identify GW sources or study their propagation, but how accurate are these ray-tracing models? How well do they agree with reality?

GLORIA measurements and their ray-traces are compared to hourly ERA5 reanalysis data. ERA5 can reproduce the main wave components very well, however small scale perturbations with horizontal wavelengths below 150 km are not resolved by the model. Thus, only ray-traces of the larger scale GWs are used for the comparison. The GW event above Iceland is characterized by strong oblique propagation. The waves above Scandinavia propagate more or less straight upwards. The linear ray-tracing results show an excellent agreement with ERA5 for both cases.

In the middle stratosphere, the results of both models are compared to AIRS satellite measurements. Due to the relatively short vertical wavelengths of less than 15 km at 35 km altitude, the wave signatures are strongly suppressed in AIRS temperatures. However, by including the AIRS observational filter into the comparison good agreement between AIRS and models is achieved.