Processes And Climatology Of Gravity waves (PACOG)

PIs:
Prof. Dr. Franz-Josef Lübken, Prof. Dr. Jorge Chau, Dr. Gerd Baumgarten,  IAP Kühlungsborn,
Prof. Dr. Markus Rapp, Dr. Andreas Dörnbrack,  IPA DLR Oberpfaffenhofen

PhD students and Postdocs:
Dr. Irina Strelnikova (IAP), Robert Reichert (DLR), Kathrin Baumgarten (IAP), Dr. Bernd Kaifler (DLR); Benedikt Ehard (DLR), Raimund Wörl (IAP)

Figure 1 The Photograph of Radar and Lidar at Andoya

PACOG is a project within the Research Unit MS-GWaves which is dedicated to the general study of gravity waves. PACOG concentrates on atmospheric observations and comparison with models.
Gravity waves play a key role in our understanding of the middle atmosphere since they drive the atmosphere away from radiatively determined conditions by up to 100 K and impose drastic changes on circulation systems and composition. They are the most important coupling mechanism from below to above. Unfortunately, many processes related to gravity waves are not well understood. This concerns, for example, generation, propagation, filtering, dissipation as well as seasonal and temporal variability. We intend to study the climatology of gravity waves on regional and global scales, and also their relevance for global processes. We will apply a combination of sophisticated and comprehensive instrumentation (lidars, radars, sensors on satellites, etc.) and will interpret our measurements with the help of related simulations based on reanalysis data. The final aim of MS-GWaves is to improve the parametrization of gravity waves used in global models. Observations performed in PACOG shall be used in all projects of MS-GWaves, for example when comparing local and regional measurements with global observations from satellites (SV project) or as benchmark tests for the validation of modeling in the 3DMSD and GWING projects.

alomar kborn and ratio s
Figure 2. The climatology of gravity wave potential energy density (GWPED) obtained from the RMR lidar at ALOMAR (upper panel) and Kühlungsborn (middle panel) during night- and daytime. The ratio between GWPED obtained at two different stations is demonstrated in lower panel


In the first phase of the project the climatology of gravity wave potential energy density (GWPED) was obtained from the RMR lidar at Kühlungsborn during night- and daytime.

Figure 3. Zonal, meridional wind, and temperature perturbations on 21 to 23 January 2012, after removing low frequency variations. Horizontal bars indicate the observed period and vertical arrows show the propagation direction at times of the hodograph analysis. Such fluctuations are used to derive GW parameters from ground based observations

We made use of the DoRIS setup implemented in the RMR lidar at ALOMAR (69°N) to measure winds and temperatures simultaneously in the middle atmosphere.
During the first phase of PACOG we measured and analyzed temperatures and winds between 20 and 80 km. Also, climatology of seasonal variations of mean winds, tides, and gravity waves was obtained using the continuous radar measurements at ALOMAR and Juliusruh. The new MMARIA concept was developed, which allows measuring horizontally resolved winds making use of a network of active and passive meteor radars. This concept provides a new possibility to investigate the spatial and temporal evolution of GWs in the mesosphere.

A detailed case study of an observed mountain wave event under transient tropospheric forcing was conducted. The combined airborne and ground-based measurements were part of the DEEPWAVE campaign in New Zealand in austral winter 2014. To investigate the impact of the transient forcing conditions on the deep vertical gravity wave propagation, the comprehensive set of airborne and ground-based measurements was combined with operational analysis and short-term forecasts of the ECMWF (European Centre for Medium-Range Weather Forecasts) integrated forecast system (IFS)


Apart from the DEEPWAVE campaign in New Zealand, a comprehensive field campaign was conducted in Northern Scandinavia in the winter of 2015/2016 which involved several lidars, radars, airglow instruments etc., as well as several aircraft and balloons. This was presumably the largest field campaign ever conducted in that region.

In the second phase we plan to investigate the temporal and spatial variability of tides and gravity waves, the importance of local sources ('hot spots') for GW effects in the strato/mesosphere, the importance of secondary GWs for the dynamics of the middle atmosphere, the GW coupling of troposphere/middle atmosphere during selected scenarios, and the dissipation of gravity waves.

The final aim of MS-GWaves is to improve the parametrization of gravity waves used in global models. Observations performed in PACOG shall be used in all projects of MS-GWaves, for example when comparing local and regional measurements with global observations from satellites (SV project) or as benchmark tests for the validation of modeling in the 3DMSD and GWING projects.

Publications