The model concept facilitates to easily connect additional tracers and modules of different focus and complexity. At the moment, the model consists of eight modules:
- The dynamic part solves the Navier-Stokes equation for the gas-particle-mixture and includes the transport of active tracers (Oberhuber et al., 98; Herzog, 98).
- The turbulence closure scheme delivers the turbulent exchange coefficients for each dynamic quantity, thereby describing the entrainment of ambient air into the plume (Herzog, 98; Oberhuber et al., 98).
- The cloud microphysics describes condensation of water vapour and formation of precipitation predicting the specific mass content and the number concentration of each class. All phases of water are included: vapour, liquid and solid. The feedback of the of thermal energy changes on the dynamics is considered (Graf et al., 99; Herzog et al., 98; Textor, 99).
- The aerosol module describes particle growth and coagulation based on microphysical interactions between hydrometeors and ash (Textor, 99).
- The soil module determines the amount of settled ash particles and hydrometeors, providing a consistent lower boundary condition for temperature and humidity.
- The scavenging module calculates dissolution of volcanic gases into droplets and the incorporation of volatiles into ice particles. The redistribution of species contained in hydrometeors due to microphysical processes is included (Textor et al. 2002).
- Radiative forcing due to absorption and scattering of terrestrial and solar radiation is treated by an on-line delta-eddington scheme (Trentmann, pers. comm.).
- The chemistry module calculates the gas phase chemistry in the plume (Trentmann, pers. comm.).