# Gaussian grid

A **Gaussian grid** is used in the earth sciences as a gridded horizontal coordinate system for scientific modeling on a sphere (i.e., the approximate shape of the Earth). The grid is rectangular, with a set number of orthogonal coordinates (usually latitude and longitude).

The gridpoints along each latitude (or *parallel*), i.e., the longitudes, are *equally* spaced. Thus, at each latitude, the distance between any two adjacent degrees of longitude is the same. However the gridpoints along each longitude (or *meridian*), i.e., the latitudes, are *unequally* spaced: the distance between adjacent degrees of latitude will vary. Instead, spacing of latitudes is defined by the Gaussian quadrature. By contrast, in the "normal" geographic latitude-longitude grid, gridpoints are equally spaced along both latitudes and longitudes. Gaussian grids also have no grid points at the poles.

In a *regular* Gaussian grid, the number of gridpoints along the longitudes is constant, usually double the number along the latitudes. In a *reduced* (or *thinned*) Gaussian grid, the number of gridpoints in the rows decreases towards the poles, which keeps the gridpoint separation approximately constant across the sphere.

## Examples of Gaussian grids

- CCCma global climate models of climate change
- European Centre for Medium-Range Weather Forecasts [1]
- Features for ERA-40 grids

## See also

## References

- NCAR Command Language documentation
- W.M. Washington and C.L. Parkinson, 2005. An Introduction to Three-Dimensional Climate Modeling. Sausalito, CA, University Science Books. 368 pp.
- Hortal, Mariano, and A. J. Simmons, 1991. Use of reduced Gaussian grids in spectral models. Monthly Weather Review 119.4 : 1057-1074.