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 base or within Pinatubo aerosol layer. The temperature was generally below -35-degrees-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-degrees-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.