Model Resolution » Spectral Resolution

In spectral models, the horizontal resolution is designated by a "T" number, which indicates the number of waves used to represent the data. The "T" stands for triangular truncation, which indicates the particular set of waves used by a spectral model.

Spectral models represent data precisely out to a maximum number of waves, but omit all, more detailed information contained in smaller waves. This is in contrast to gridpoint models, which try to represent all scales but poorly handle waves only a few grid points across.

The wavelength of the smallest wave in a spectral model is represented as minimum wavelength = 360 degrees/N

where N is the total number of waves (the "T" number).

For example, a T80 model could resolve a wavelength of 360/80 = 4.5 degrees.

Complications arise because nonlinear dynamics and physics are calculated on a grid and then converted to spectral form to incorporate their effects in a spectral model. This introduces errors, which make the final result less exact than one might expect from calculations done strictly in spectral space.