Abstract
Abstract. To study the feasibility of a fluorescence lidar for aerosol characterization, the fluorescence channel is added to the LILAS multiwavelength Mie–Raman lidar of Lille University, France. A part of the fluorescence spectrum induced by 355 nm laser radiation is selected by the interference filter of 44 nm bandwidth centered at 466 nm. Such an approach has proved to have high sensitivity, allowing fluorescence signals from weak aerosol layers to be detected and the fluorescence backscattering coefficient from the ratio of fluorescence and nitrogen Raman backscatters to be calculated. Observations were performed during the November 2019–February 2020 period. The fluorescence capacity (ratio of fluorescence to elastic backscattering coefficients), measured under conditions of low relative humidity, varied in a wide range, being the highest for the smoke and the lowest for the dust particles. The results presented also demonstrate that the fluorescence measurements can be used for monitoring the aerosol inside the cloud layers.
Highlights
Aerosol–cloud interactions are one of the key factors influencing the Earth radiation balance, and, for its realistic modeling, knowledge of aerosol properties both outside and within the cloud layer is needed
The fluorescence spectrum varies with aerosol type and composition, making their identification possible
On 6–7 February the aerosol loading in the planetary boundary layer (PBL) is very low (β1064 < 0.003 Mm−1 sr−1 at 1000 m), and relative humidity (RH) from the radiosonde at Herstmonceux is below 40 % in the height range considered
Summary
Aerosol–cloud interactions are one of the key factors influencing the Earth radiation balance, and, for its realistic modeling, knowledge of aerosol properties both outside and within the cloud layer is needed. Useful for studying aerosol, the amount of information contained in these measurements remains limited (Burton et al, 2016; Alexandrov and Mishchenko, 2017). Such lidars are not able to detect and characterize aerosol inside a cloud layer because aerosol scattering is masked by strong cloud particle scattering. To improve the lidar capability for aerosol characterization, additional channels, measuring the laser-induced fluorescence, can be used. Numerous types of atmospheric aerosols, such as biological, biomass burning particles, sulfates and even dust, are fluorescent, being excited by UV radiation. Due to the fact that pure water does not fluoresce, the measurement of cloud fluorescence allows information to be obtained about aerosol particles within the cloud layer, at least near the cloud base, allowing aerosol–cloud coexistence to be investigated
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