[swash-users] problems with boundary conditions, for nested runs using SWAN generated spectrum

[Marco M. <mar...@un...>]

Hi out there. 

I have a problem I can't seem to explain to cause of, maybe someone out there has already bumped into this and can help. 

I nest a smaller SWASH run (high res) into a larger SWAN run. The latter is forced by some wave measurements and provides the former with spectral boundary conditions at nesting interface. SWAN outputs a wave spectrum with a 2 meters significant wave height. When I run swash, I see that run-up on the sand dune is miserably below my expectations. I have been inspecting the boundary condition the model propagates by taking surface levetion for one point at SWASH boundary. 

After inspecting the time-series taken at the model boundary (SWASH) I clearly see that there is no chance of Hm0 being consistent at the nesting boundary ("from SWAN to SWASH"). User prescribed (and SWAN provided) spectrum has a Hm0=2 m. SWASH produced spectrum (at boundary) has a Hm0 of approx 20 cm. One order of magnitude smaller. 

Why is this? How can I possible fix this? How can I simply pass on the information from SWAN to SWASH an complete my model chain? Enclosed some images. 

Thank you. 
Cheers
Marco