The solution of the momentum equations is done within the DYNAM. The scheme is leap frog in time with an initial 2/3 time step every 8 leap-frog steps to prevent solution splitting. The dynamics are based on the dry physics (no water vapour effects in the pressure gradient calculation) and use potential temperature as the advected variable. Water vapour and tracers are advected outside the dynamics loop (once every source time step). All temperature, water and tracer advection is done using the quadratic upstream scheme to minimise numerical diffusion.