Impact of Various Observing Systems on NWP—Outcomes of the 5th WMO workshop

The 5th WMO workshop on the impact of various observing systems on numerical weather prediction was held 22-25 May 2012 in Sedona, Arizona (United States). The workshop was attended by 56 experts on data assimilation and observation impact, representatives from space agencies and managers of observing networks from 13 countries.

A summary of the main outcomes of the workshop will be presented.

Several of the global NWP centres presented detailed assessments of the impact on forecast skill of the main meteorological observing systems. The traditional technique to assess the impact of observations is to conduct observing system experiments (OSEs) where the forecast impact of perturbations in the assimilated observational data set is measured against the forecast performance of an unperturbed (control) assimilation. In recent years several new techniques that augment the OSE results have been developed and they are now widely adopted, notably adjoint based tools such as Forecast Sensitivity to Observations (FSO), Degrees of Freedom for Signal (DFS) and others.

A substantial body of results was presented demonstrating beneficial impacts on regional NWP from various components of the heterogeneous observing systems. Current regional NWP systems use 3D or 4D data assimilation techniques at high horizontal resolution (2 to 10 km) with short data cut-off times. In regional NWP, it was found that the observing systems providing the highest impact are different from that in global NWP; there are also substantial differences between the respective results reported by different regional NWP centres.