  A combined high-resolution atmospheric downscaling and wave hindcast based on
the ERA-40 reanalysis covering the Norwegian Sea, the North Sea and the Barents
Sea is presented. The period covered is from September 1957 to August 2002. The
dynamic atmospheric downscaling is performed as a series of short prognostic
runs initialized from a blend of ERA-40 and the previous prognostic run to
preserve the fine-scale surface features from the high-resolution model while
maintaining the large-scale synoptic field from ERA-40. The nested WAM wave
model hindcast consists of a coarse 50 km model covering the North Atlantic
forced with ERA-40 winds and a nested 10-11 km resolution model forced with
downscaled winds.
  A comparison against in situ and satellite observations of wind and sea state
reveals significant improvement in mean values and upper percentiles of wind
vectors and the significant wave height over ERA-40. Improvement is also found
in the mean wave period. ERA-40 is biased low in wind speed and significant
wave height, a bias which is not reproduced by the downscaling. The atmospheric
downscaling also reproduces polar lows, which can not be resolved by ERA-40,
but the lows are too weak and short-lived as the downscaling is not capable of
capturing their full life cycle.
