Seasonal cycle of gravity wave potential energy densities from lidar and satellite observations at 54° and 69°n

Abstract

We present gravity wave climatologies based on 7 years (2012 18) of lidar and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperatures and reanalysis data at 548 and 698N in the altitude range 30 70 km. We use 9452 (5044) h of lidar observations at Köhlungsborn [Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR)]. Filtering according to vertical wavelength (lz,15 km) or period (t ,8 h) is applied. Gravity wave potential energy densities (GWPED) per unit volume (EpV) and per unit mass (Epm) are derived. GWPED from reanalysis are smaller compared to lidar. The difference increases with altitude in winter and reaches almost two orders of magnitude around 70 km. A seasonal cycle of EpV with maximum values in winter is present at both stations in nearly all lidar and SABER measurements and in reanalysis data. For SABER and for lidar (with l , 15 km) the winter/summer ratios are a factor of ;2 4, but are significantly smaller for lidar with t , 8 h. The winter/summer ratios are nearly identical at both stations and are significantly larger for Epm compared to EpV. Lidar and SABER observations show that EpV is larger by a factor of ;2 at Köhlungsborn compared to ALOMAR, independent of season and altitude. Comparison with mean background winds shows that simple scenarios regarding GW filtering, etc., cannot explain the Köhlungsborn ALOMAR differences. The value of EpV decreases with altitude in nearly all cases. Corresponding EpV-scale heights from lidar are generally larger in winter compared to summer. Above ;55 km, EpV in summer is almost constant with altitude at both stations. The winter summer difference of EpV scale heights is much smaller or absent in SABER and in reanalysis data.