Year-round stratospheric aerosol backscatter ratios calculated from lidar measurements above northern Norway

摘要

We present a new method for calculating backscatter ratios of the stratospheric sulfate aerosol (SSA) layerfrom daytime and nighttime lidar measurements. Using this new method we show a first year-round dataset of stratospheric aerosolbackscatter ratios at high latitudes. The SSA layer is located at altitudes between the tropopause and about 30 km. It is offundamental importance for the radiative balance of the atmosphere. We use a state-of-the-art Rayleigh–Mie–Raman lidar at theArctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) station located in northern Norway (69∘ N,16∘ E; 380 m a.s.l.). For nighttime measurements the aerosol backscatter ratios are derived using elasticand inelastic backscatter of the emitted laser wavelengths 355, 532 and 1064 nm. The setup of the lidar allows measurements with a resolution of about 5 min in time and 150 m in altitude to be performed in high quality, which enables the identification of multiple sub-layers in the stratospheric aerosol layer of less than 1 km vertical thickness. We introduce a method to extend the dataset throughout the summer when measurements need to be performed under permanentdaytime conditions. For that purpose we approximate the backscatter ratios from color ratios of elastic scattering and applya correction function. We calculate the correction function using the average backscatter ratio profile at 355 nmfrom about 1700 h of nighttime measurements from the years 2000 to 2018. Using the new method we finally present ayear-round dataset based on about 4100 h of measurements during the years 2014 to 2017.