An uncoupled dynamical downscaling for the North Sea: Method and evaluation

A reliable regional modeling system for uncoupled dynamical downscaling simulations of potential global climate change scenarios in the North Sea is presented. The HAMSOM regional shelf ocean model is forced with results from the MPIOM global ocean model at the open lateral boundaries of the model domain, and with results from the REMO regional atmosphere model at the air-sea interface. The evaluation of the model chain is based on the North Sea regionalization for the period 1951-2000 of the global historic control run 20C3M for the IPCC SRES scenario runs under the CMIP3 model generation. To reproduce reasonable long-term statistics of hydrodynamic conditions in the North Sea, a bias correction method relative to ERA40 reanalysis data and WOA-2001 climatology is applied to the forcing variables. Comparisons of the HAMSOM model results with observational water temperature and salinity climatologies are presented as well as with previously published research of volume transports, residence and flushing times, NAO correlations, surface heat and fresh water fluxes, and thermocline parameters. In general, the model results agree reasonably with the given references, thereby qualifying the presented concept as an appropriate tool for dynamical downscaling of global scenario runs for the North Sea.