  As atmospheric models move to higher resolution and resolve smaller scales,
the maximum modeled wind speed also tends to increase. Wave models tuned to
coarser wind fields tend to overestimate the wave growth under strong winds. A
recently developed semi-empirical parameterization of the Charnock parameter,
which controls the roughness length over surface waves, substantially reduces
the aerodynamic drag of waves in high winds (above a threshold of 30 m/s). Here
we apply the formulation in a recent version of the wave model WAM (Cycle 4.7),
which uses a modified version of the physics parameterizations by Ardhuin et al
(2010) as well as subgrid obstructions for better performance around complex
topography. The new Charnock formulation is tested with wind forcing from
NORA3, a recently completed non-hydrostatic atmospheric downscaling of the
global reanalysis ERA5 for the North Sea, the Norwegian Sea and the Barents
Sea. Such high-resolution atmospheric model integrations tend to have stronger
(and more realistic) upper-percentile winds than what is typically found in
coarser atmospheric models. A two-year comparison (2011-2012) of a control run
against the run with the modified Charnock parameter shows a dramatic reduction
of the wave height bias in high-wind cases. The added computational cost of the
new physics and the reduction of the Charnock parameter compared to the earlier
WAM physics is modest (14%). A longer (1998-2020) hindcast integration with the
new Charnock parameter is found to compare well against in situ and altimeter
wave measurements both for intermediate and high sea states.
