Multispectral lidar data measured at Sodankylä (67°N, 26°E), have been used to characterize stratospheric aerosols. Using depolarization measurements, particles have been classified into PSC and volcanic aerosols. While Pinatubo aerosol could be observed inside the polar vortex from the beginning of the campaign, only few PSC events have been observed. For Pinatubo aerosol lognormal size distribution parameters have been retrieved, indicating particle distributions with 0.1 µm to 0.3 µm median‐radius between 17 and 22 km and up to 0.7 µm below. Height resolved size distribution parameters and aerosol surface areas are given.

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Multiwavelength lidar measurements carried out in Sodankylä (Finland, 66°N) during EASOE campaign showed high cirrus clouds growing at the base or within Pinatubo aerosol layer. The temperature was generally below −35°C. The mean peak depolarization at 532 nm for all the campaign was 28%, comparable to the values measured in polar cirrus clouds, observed in Dumont d'Urville (Antarctica, 62°S) during 1989, well before the Pinatubo eruption. Optical depth at 532 nm was smaller than 0.3 (thin cirrus). A wavelength dependency was observed in EASOE cirrus backscattering, suggesting a major presence of submicron and micron‐sized particles. Such a presence could explain the low depolarization values.

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A new inversion algorithm has been developed to determine the aerosol size distribution, from LIDAR signals obtained at several wavelengths. This algorithm is based on a non linear fit of the backscattered measurements using a set of predetermined functions. Two function types have been taken into account to describe the size distribution of tropospheric aerosols: Junge distribution for clear atmosphere and log normal distribution for fogs and clouds. This method has been tested using a four-wavelengths Lidar system (300 nm, 600 nm, 695nm, 760 nrn). Lidar measurements made in Central Switzerland (Rigi), characterized by a specific micro-climate, allowed to determine size distribution profiles of tropospheric aerosols in different meteorological conditions: clear, hazy, and cloudy atmosphere. The distribution parameters (concentration, mean radius, standard deviation) have hence been obtained. Stratospheric clouds and aerosols, created by the Pinatubo eruption have been measured above Berlin and Sodankylä (Finland) with a Lidar at five wavelengths: 355 nm, 532 nm (Nd:Yag), 750 nm, 800 nm anl 850 nm (flashlamp-pumped Ti:Sapphire). These measurements were used to characterize the size distribution of these volcanic aerosols in order to estimate their influence on radiative transfers. Depolarisation measurements were performed to distinguish between different types of aerosols.