Tropospheric aerosol layers after a cold front passage in January 2000 as observed at several stations of the German Lidar Network

Using the German Lidar Network, we analysed 2 years of lidar observations of aerosol layers. Here we report in particular on a cold front event in January 2000 with Rayleigh/Mie/Raman lidar measurements taken both in the boundary layer as well as in the free troposphere at four different sites. After the cold front passage, and while the air mass travelled from northern to southern Germany, the aerosol backscatter coefficient increased in the lower troposphere but not in the free troposphere. Behind the front, an aerosol layer was observed in the free troposphere at all stations. To characterize changes in the aerosol layer as it moved from northern to southern Germany, backscatter profiles measured at Kühlungsborn and Hamburg were compared with profiles at Leipzig and Garmisch-Partenkirchen, respectively. This case study shows that an aerosol layer can persist in the free troposphere over a period of a few days. From calculated backward trajectories, we conclude that the air mass was lifted from the boundary layer, most likely 2–3 days before the cold front reached the lidar stations in Germany. We also compare the results of different trajectory models with respect to the origin of the aerosol layer. They indicate continental aerosols from the center of the North American continent, which is consistent with particle size inversion results from the lidar backscatter data.