MULTIWAVELENGTH LIDAR OBSERVATION OF THIN CIRRUS AT THE BASE OF THE PINATUBO STRATOSPHERIC LAYER DURING THE EASOE CAMPAIGN

Multiwavelength lidar measurements carried out in Sodankyla (Finland, 66-N) during EASOE campaign showed high cirrus clouds growing at the b ase or within Pinatubo aerosol layer. The temperature was generally be low -35-degrees-C. The mean peak depolarization at 532 nm for all the campaign was 28%, comparable to the values measured in polar cirrus cl ouds, observed in Dumont d'Urville (Antarctica, 62-degrees-S) during 1 989, well before the Pinatubo eruption. Optical depth at 532 nm was sm aller 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 depo larization values.