Three years of routine Raman lidar measurements of tropospheric aerosols: Backscattering, extinction, and residual layer height

[摘要] We have performed a three-year series of routine lidarmeasurements at preselected times. The measurements were performed between 1 December 1997, and 30 November 2000, atKühlungsborn, Germany (54°07' N, 11°46' E). Using a Rayleigh/Mie/Raman lidarsystem, we measured the aerosol backscatter coefficients at three wavelengths and the extinction coefficient at one wavelength. Thepresent data analysis focuses on after-sunset Raman measurements obtained on cloud-free days. Aerosol backscatter profiles areavailable for altitudes above 100 m, while the majority of the extinction measurements has been restricted to heights above theresidual layer. The residual layer shows an annual cycle with its maximum height in summer (2000 m) and minimum height in winter(850 m). The backscatter coefficients in the residual layer were found to be about10 times higher than above. The mean aerosol optical depth above the residual layer and below5 km is 0.3(±1.0) x10^-2 in summer, and 1.5(±1.0) x10^-2 in winter, which almost is negligiblecompared to values measured in during daytime in the planetary boundary layer. A cluster analysis of the backward trajectoriesyielded two major directions of air mass origin above the residual layer and4 major directions inside. A marked difference between the aerosol properties dependent on the air mass origin could befound for air masses originating from the west and travelling at high wind speeds. Comparing the measured spectral dependence ofthe backscatter coefficients with data from the Global Aerosol Data Set, we found a general agreement, but only a few conclusionswith respect to the aerosol type could be drawn due to the high variability of the measured backscatter coefficients.

[学科分类] 大气科学