Simulation der Dynamik eines Multikomponentensystems am Beispiel vulkanischer Eruptionswolken

The Active Tracer High Resolution Atmospheric Model (ATHAM) has been improved using a mass and momentum conservative formulation of the model equations and the introduction of a turbulence closure scheme. ATHAM has been tested simulating a typical plinian eruption. ATHAM describes a multicomponent system consisting of gaseous and incompressible fractions under the assumption of a dynamic and thermal equilibrium. The turbulence closure scheme is based on turbulent energy equations and provides for a turbulent exchange coefficient for each dynamic quantity distinguishing between horizontal and vertical exchange. The microphysics is based on Kessler type parametrizations including the icephase. ATHAM is fully three dimensionally formulated with an implicit time step scheme. In addition there are two different types of two dimensional versions implemented: one represents two dimensional cartesian coordinates, the other cylindrical coordinates. The description of a multicomponent system with ATHAM is numerically stable and physically correct, as can be seen from the two dimensional model simulations which includes many active tracers and an incompressible fraction up to 99 weight percentage. The simulated eruption plumes reach into the stratosphere and achieve a horizontal extension in the order of 100 km. Transport processes due to turbulence are as important as those due to advection. Turbulent processes determine the entrainment of ambient air, the plume development and height. The effect of microphysical processes on the plume dynamics is dominated by the amount of entrained water vapour. It is the actual weather conditions at the time of the eruption as well as the mean meteorological state of the atmosphere that have a strong impact on the plume height and the amount of particles and volcanic gases injected into the stratosphere. (orig.)Available from TIB Hannover: RR 9(53) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman