The impact of wave number selection and spin-up time in spectral nudging

Abstract

The present work studies two relevant parameters from spectral nudging. First, the cut-off wave number, which effectively separates the nudged scales from the free running ones. And, second, the spin-up time, which determines how much time is needed to reach a balance between the nudging force and the model internal climate. Our results show that the optimal cut-off wave number coincides with the Rossby Radius of Deformation, both in mid and tropical latitudes, suggesting that this parameter is related with the dynamic characteristics of the modelled area, and not with features of the experiment design. The optimal spin-up time is found to be 24/48h for mid latitudes and 72/96h for tropical latitudes. We also study the suitability of spectral nudging as an initialisation technique. Our results indicate that it is beneficial to use some nudging technique at the beginning of the simulation, but we have not found relevant differences between grid nudging and spectral nudging.