On the time-splitting errors of one-dimensional advection schemes in numerical weather prediction models; a comparative study

摘要

A one-dimensional flux-form advection scheme with a new correction of time-splitting errors is implemented in the numerical weather prediction (NWP) model COSMO of the German Meteorological Service. The advection scheme is applied for calculating thetransport of all prognostic humidity variables in COSMO. Moreover, the advective transport of passive tracers is investigated. With the modified COSMO configuration, several realistic case-studies are performed and compared with the operational COSMO version. The main focus of these investigations is on the behaviour of the new advection scheme in regions with strong deformational flow fields, such as steep orographical terrain and meteorological fronts.The numerical results of these case-studies indicate that the modified COSMO model yields results similar to the operational version. The observed differences between the two model versions are minimized when the advection scheme of the operational COSMO model is applied with a numerically expensive Strang splitting approach. At the same time, the results of the new advection scheme are barely affected by the application of Strang splitting. Since, in addition to this, the new advection scheme behaves numerically more stably than the original scheme, it is an attractive alternative for calculating the transport of scalar quantities in NWP models.