Spectral nudging is a technique to keep the larger spatial scales of a limited area model (LAM) close to the larger spatial scales of its driving model, whereas the smaller spatial scales can develop freely. To do this, one gently "nudges" the larger spatial scales of a few dynamic fields (usually u- and v-wind and sometimes temperature as well) towards the larger spatial scales of the driving model. The nudging is usually stronger at higher altitudes than at lower altitudes. In GEM, the strength of the spectral nudging can get adjusted though parameters in the gem_settings.nml 'spn' namelist.
Spectral nudging parameters in GEM:
GEM 3.3.3.1 (CRCM5)
GEM 4 and upnewer versions
References:
- Xu Z. and Z.-L. Yang (2015): A new dynamical downscaling approach with GCM bias corrections and spectral nudging. J. Geophys. Res. Atmos., 120, 3063–3084
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