Multiphase Flows in the Atmosphere

Abstract

Phase change of water vapour in the atmosphere produces small water particles in the atmosphere. They are usually suspended quite densely in limited space and are called clouds. When the air temperature falls below -20°C, they are replaced by ice particles. Clouds play an important role in the meteorological processes from local to global scales.Pyroclastic flow is a complicated multiphase flow associated with volcanic eruptions. It consists of a mixture of air and hot volcanic ash and behaves like a gravity current along mountain slopes. Since the air is heated by hot ash, buoyancy in the pyroclastic flow increases like cumulus in which the air is heated by the latent heat of water.Powder snow avalanche is a kind of turbidity currents, which occurs when a large amount of powder snow accumulates in piles along the moutain slope. Once the avalanche begins, turbulence in the avalanche takes the piled snow into the air along the path and the effective density increases. The powder snow avalanche is very destructive, because the velocity reaches about 100m/s in the developed stage.