Investigation of the life cycle of internal gravity waves (GW-LCYCLE)

The project GW-LCYCLE addresses the fundamental issue of internal gravity wave (IGW) excitation, propagation, and dissipation in the atmosphere. IGWs are one of the most important dynamical coupling processes between the troposphere and the middle atmosphere (10 to 120 km). IGWs couple different atmospheric regions both in the vertical as well as in the horizontal directions by means of momentum and energy transport. Notably, this coupling is effective both from the troposphere upwards, and also in the opposite direction by indirect effects on circulation patterns. While this importance of IGWs for understanding atmospheric structure, dynamics and climate is now widely recognized surprisingly little is still known about the details of the actual life cycle of IGWs.

To address this issue, coordinated field campaigns deploying ground-based and airborne observations will be conducted. The results of these remote-sensing and in-situ measurement will be combined with state-of-the art numerical modelling as well as global observations of satellites.

Ground-based and airborne observation of IGW signatures will be conducted over Northern Scandinavia.  The paths of the forecasted IGWs will be traced back to their likely source regions using ray tracing techniques.  These source regions will then be verified experimentally using the airborne measurements involving two different aircraft, i.e., the DLR research aircraft FALCON and the German HALO research aircraft. Both aircraft will be operating at different altitudes around the tropopause to allow simultaneous gravity wave observations in the troposphere and stratosphere.

One of the key-instruments of the project is the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA). GLORIA is a novel instrument for infrared limb imaging of the atmosphere. Under cloud-free conditions, GLORIA measures temperature and a number of trace species at altitudes between 4 km and the flight altitude. For closed flight legs (e.g. as hexagons) 3D distributions can be retrieved with a spatial resolution better than 25 km in the horizontal and 500 m in the vertical. This allows the full characterization of single waves in terms of temperature amplitude and the 3D wave vector.

The combination of GLORIA observations with those of other in-situ and remote-sensing instruments (e.g. the airborne fast airglow imager FAIM) enables us to study the life cycle of IGWs from their source regions to their dissipation altitude.  The combined results will then provide critical input to idealized numerical simulations using state of the art numerical models. The combined results will deliver constrains for gravity wave parameterizations which are needed to describe IGW effects in global circulation models.