8.2.1 Atmospheric Processes
In the TAR, more than half of the participating atmospheric models used spectral advection. Since the TAR, semi-Lagrangian advection schemes have been adopted in several atmospheric models. These schemes allow long time steps and maintain positive values of advected tracers such as water vapour, but they are diffusive, and some versions do not formally conserve mass. In this report, various models use spectral, semi-Lagrangian, and Eulerian finite-volume and finite-difference advection schemes, although there is still no consensus on which type of scheme is best.