Spectrum tail and interaction source term

[Jialunx]

Dear team,

I have observed that the spectrum tail can have a substantial impact on the WRT/DIA source term. The spectrum is retrieved from ECWMF with a frequency range of up to 0.54 Hz (a total of 30 frequency indices). As shown in the figure, the WRT behavior exhibits a large difference between extend with an exponential decay (top panel) and extend with 0 beyond 0.54 Hz (bottom panel). I am wondering whether it is appropriate to extend an exponential decay or if there is an alternative approach to handling the spectrum tail.

Thank you very much.