1. Potential of the ATHAM model for use in air traffic safety Gerald GJ Ernst Geological Institute, University of Ghent, Gent, Belgium Christiane Textor Lab. des Sciences du Climat et de l’Environnement, CEA-CNRS, Gif-sur-Yvette, France Michael Herzog Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan. Hans-F Graf Department of Geography, University of Cambridge, Cambridge, UK Josef M Oberhuber formerly at Deutsches Klima Rechenzentrum, Hamburg, Germany

2. Aerosol Interaction of hydrometeors and particles Ash aggregation (Textor et al. 2003) Processes simulated by the ATHAM model Dynamics Advection and thermodynamics of the gas-particle mixture (Oberhuber et al. 1998, Herzog 1998) Turbulence Entrainment of ambient air, Prediction of turbulent energy and length scale (Oberhuber et al. 1998, Herzog et al. 2003) Microphysics Cloud and precipitation processes, release of latent heat (Graf et al. 1999, Herzog et al. 1998, Textor 2003) Gas scavenging By water and ice (Textor et al. 2003) ATHAM: A ctive T racer H igh Resolution A tmospheric M odel

3. ATHAM 3d Simulation Max-Planck-Institute for Meteorology Herzog M, Oberhuber JM, Graf H:A prognostic turbulence scheme for the nonhydrostatic plume model ATHAM, J ATMOS SCI 60 (22): 2783-2796 2003 Typical plinian eruption conditions in a tropical atmosphere Model spin-up of 45 min 60 min of eruption Model domain of 250x200x50 km 3, 127x107x127 grid points Stretched grid with100m resolution at the volcano and some kilometers at the model boundaries Cloud microphysics with water and ice, precipitation development No ash aggregation Visualisation: M. Böttinger Deutsches Klima Rechenzentrum

4. Model Setup Conditions at the eruption column base Mountain height2500m Width of base300m Temperature1073 K Gas mass fraction 6 % by mass Water vapor mass fraction of tot. gas50% by mass Bulk density of the gas particle mixture~3.1 kg/m 3 Vertical velocity at eruption column base250 m/s Mass eruption rate~5.55 10 7 kg/s

5. Model Setup Particle properties Particle density 2000 kg/m 3 Three particle classes1/3 by mass each Particle sizes [  m]10 200 4000 Terminal fall velocity at 1bar [m/sec]0.024 3.2 15.2

6. Model Setup Background Atmosphere Vertical profiles for tropical conditions temperature humidity cross wind

7. Volcanic ash in a plume of an explosive eruption ATHAM 3d simulation Max-Planck-Institute for Meteorology Ash sizes 10  m 4 mm

8. Volcanic ash in a plume of an explosive eruption Ash sizes 10  m 200  m 4 mm ATHAM 3d simulation Max-Planck-Institute for Meteorology

9. Fine ash and hydrometeors during an explosive eruption fine ash liquid water ice ATHAM 3d simulation Max-Planck-Institute for Meteorology