ALBERT

Description: This paper demonstrates two important aspects of regional dynamical downscaling of multi-decadal atmospheric re-analysis. First, that in this way skillful regional descriptions of multi-decadal climate variability may be constructed in regions with little or no local data. Secondly, that the concept of large-scale constraining allows global downscaling, so that global re-analyses may be completed by additions of consistent detail in all regions of the world. Global re-analyses suffer from inhomogeneities. However, their large-scale componenst are mostly homogeneous; Therefore, the concept of downscaling may be applied to homogeneously complement the large-scale state of the re-analyses with regional detail – wherever the condition of homogeneity of the description of large scales is fulfilled. Technically this can be done by dynamical downscaling using a regional or global climate model, which's large scales are constrained by spectral nudging. This approach has been developed and tested for the region of Europe, and a skillful representation of regional weather risks – in particular marine risks – was identified. We have run this system in regions with reduced or absent local data coverage, such as Central Siberia, the Bohai and Yellow Sea, Southwestern Africa and the South Atlantic. Also a global simulation was computed, which adds regional features to prescribed global dynamics. Our cases demonstrate that spatially detailed reconstructions of the climate state and its change in the recent three to six decades add useful supplementary information to existing observational data for mid-latitude and sub-tropical regions of the world.