Comparison between microphysical model simulation and observed cirrus clouds formation within a volcanic aerosol layer in the Tropical Tropopause Layer

East-West Center, University of Hawai'i at Manoa (Honolulu, Hawai'i)

In order to know the formation process of cirrus clouds in tropical tropopause layer, we used a microphysical numerical model to calculate nucleation and growing process of cirrus cloud particles, and compared the results of the model simulations with observed results. The observations compared had been performed at Biak, Indonesia in January 2011. Formation of cirrus clouds was observed by lidar in an aerosol layer at the altitude from 17.5 to 19 km. The backscatter coefficient of cirrus clouds was 10^-8~10^-7/m/str and number concentration was estimated less than 10⁵/m³. Calculated results by model assumed only heterogeneous nucleation or only homogeneous nucleation (cooling rate < 0.1K/h) show agreements with the observed values. However, if there are solid and liquid aerosol particles, the simulations with heterogeneous nucleation show better agreement with the observation.