Advection of aerosol particles in the atmosphere: volcanic ash and radioactive particles

• Author: Tímea Haszpra, Eötvös Loránd University, Institute of Theoretical Physics.


• Names of other authors: Tamás Tél, András Horányi, Péter Tasnádi.


• Oral or poster: oral.


• Downloadable presentation/poster: click here.


• Abstract:
  Investigation of the spreading of aerosol particles in the atmosphere is a question of importance. The motion of a particle is described by an ordinary differential equation. The large-scale dynamics in the horizontal direction can be described by the equations of passive scalar advection, but in the vertical direction a well-defined terminal velocity should be taken into account as a term added to the vertical wind component. In the planetary boundary layer turbulent diffusion has an important role in the particle dispersion, which is taken into account by adding stochastic terms to the deterministic equations above. The background wind field and other necessary data are taken from the ECMWF ERA-Interim database. Simulations show that advection is chaotic. Since aerosol particles released in the free atmosphere sooner or later leave this zone, chaos is transient. We point out that quantities like escape rate and average lifetime outside the boundary layer, as well as stretching rate of material line segments can efficiently be applied to characterize the volcanic ash dynamics in the free atmosphere. In the case of the Fukushima nuclear accident the majority of the pollutants was released in the boundary layer. Results show that including only the dry deposition leads to an underestimation of the overall fallout. Wet deposition is an essential process in the lower levels of the atmosphere, however its precise parameterization is a challenge.