# Common Spectral Model Grid Resolutions

Models which use spherical harmonics are called 'spectral models'.Spectral models have some advantages and disadvantages. An ECMWF workshop tutorial (which is no longer available online) stated the following:

- Advantages
- Space derivatives calculated exactly.
- Non-linear quadratic terns calculated without aliasing (if computed in spectral space or using the quadratic grid).
- For a given accuracy fewer degrees of freedom are required than in a grid-point model.
- Easy to construct semi-implicit schemes since spherical harmonics are eigenfunctions of the Helmholtz operator.
- On the sphere there is no pole problem.
- Phase lag errors of mid-latitude synoptic disturbances are reduced.
- The use of staggered grids is avoided.

- Disadvantages
- The schemes appear complicated, though they are relatively easy to implement.
- The calculation of the non-linear terms takes a long time unless the transform method is used.
- Physical processes cannot be included unless the transform method is used.
- As the horizontal resolution is refined, the number of arithmetic operations increases faster in spectral models than in grid-point models due to the Legendre transforms whose cost increases as N3.
- Spherical harmonics are not suitable for limited-area models.

Some commonly encountered spectral resolutions follow. A more extensive listing is also available.

Common Model Spectral Resolutions | |||
---|---|---|---|

Truncation | lat x lon | km at Eq | deg at Eq |

T21 | 32x64 | 625 | 5.61 |

T42 | 64x128 | 310 | 2.79 |

T62 | 94x192 | 210 | 1.89 |

T63 | 96x192 | 210 | 1.88 |

T85 | 128x256 | 155 | 1.39 |

T106 | 160x320 | 125 | 1.12 |

T159 | 240x480 | 83 | 0.75 |

T255 | 256x512 | 60 | 0.54 |

T382 | 576x1152 | 38 | 0.34 |

T799 | 800x1600 | 25 | 0.22 |

## Cite this page

National Center for Atmospheric Research Staff (Eds). Last modified 26 Nov 2017. "**The Climate Data Guide: Common Spectral Model Grid Resolutions.**" Retrieved from https://climatedataguide.ucar.edu/climate-tools/common-spectral-model-grid-resolutions

* Acknowledgement of any material taken from this page is appreciated. On behalf of experts who have contributed data, advice, and/or figures, please cite their work as well.