Covering gravity wave propagation from the troposphere to the mesosphere by combining lidar measurements with WRF-ARW modeling

Gravity waves (GWs) are responsible for the primary coupling processes between the troposphere and the middle atmosphere as they transport energy and momentum both horizontally and vertically from one region to another. Today, we still lack understanding of GW dynamics even though their importance for atmospheric processes is generally acknowledged.

The project “Investigation of the life cycle of gravity waves” (GW-LCYCLE) is part of the research initiative ROMIC (Role of the Middle atmosphere In Climate) funded by the German ministry of research. A first field phase has been conducted in November/December 2013 together with Scandinavian partners from Stockholm University and the Finnish Meteorological Institute. GW-LCYCLE aims on improving our understanding of the processes of GW excitation, propagation, and dissipation. The field program combines ground-based observations from airglow imagers, lidars, and radars with airborne and balloon-borne observations and numerical modelling. Here, we present results from ground-based lidar measurements at Alomar (69°N, 16°E) and Esrange (68°N, 21°E) which are located up and downwind of the Scandinavian Mountains, respectively. Information on GW activity, energy dissipation, and dominating vertical wavelengths in an altitude region from 30 to 65 km has been derived from atmospheric temperature profiles. Measurements under different GW forcing conditions were conducted between 24 November 2013 and 13 December 2013. Periods of strong forcing by the Scandinavian mountains show high GW activity and a dominant vertical wavelength in the GW spectrum. In contrast to that, vertical wavelengths are equally distributed under low GW activity conditions.

Results of regional numerical modeling with the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) model are reconciled with the lidar observations under different GW forcing conditions. Model-based GW parameters are derived applying the same methodology as utilized for the lidar observations. The combination of numerical simulations with lidar observations allows for an extended coverage of the GW spectrum as it extends the height range suitable for GW analysis from the lowermost edge of the lidar profiles at 30 km altitude down to the surface. Hence, the combination of model results with lidar observations allows resolving vertical wavelengths of up to 24 km.