Variation of the aerosol stratification over the Rhine Valley during Foehn development: a backscatter lidar study

Abstract

The vertical aerosol stratification within and above the Rhine Valley was studied with a backscatter lidar during FORM (Foehn in the Rhine Valley during MAP) IOPs 4-5, October 1-3, 1999. The lidar site was in Tr¨ubbach, 9° 28 E, 47° 04 N, 490 m asl. Two scintillometers were used to monitor the horizontal and the vertical wind velocity at 600 m above the Rhine Valley floor. A number of surface stations were operational in the valley, as well as a set of radiosounding stations. This provides a possibility to correlate the measurements of the aerosol stratification with the variation of the meteorological parameters defining the Foehn development. The backscatter lidar measurements during the Foehn development show the variation of the aerosol backscatter at different altitudes of the valley PBL. The combination of lidar signal gradient and lidar signal variance presents the cold-pool as an aerosol-rich layer and suggests a likely mechanism for cold-pool erosion by the Foehn air.