Meteorology and Climatology

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Climate Model Resolutions

Notes for Meteorology, Climate and Atmospheric Sciences...

Climate Model Resolutions

The numerical formulation of the equations included on the current climate models is a subject of research. The climate model resolution indicates information on this discretization process both in time and space. The two main discretization methods are the finite difference method to formulate the differential equations and the spectral method which allows analyitical expressions for the spaces derivatives. Here is specified several typical resolutions of both Spectral and Finite differences methods.

Spectral Model Grid

The spectral models uses a different methodology for space discretization based on spectral expansion (it can be considered a Galerkin approach)

More information can be found ECMWF and in the referece 1

In general the main advantage of spectral models is that space derivatives can be calculated analytically instead of numerically. Also in general the pole problem is not present. However the main disadvantages are the difficulties to include directly typical space grid physical processed (althought it can be done with a transformation method). It is mainly designed for global models and not limited-area models.

Typical Model Spectral Resolutions

Truncationlat x lonkm at Eqdeg at EqIn ICCP Reports
T2132x646255.625FAR
T4264x1283102.8125SAR
T6294x1922101.875 
T6396x1922101.875TAR
T85128x2561551.4 
T106160x3201251.125AR4
T255256x512600.703125 
T382576x1152380.313 
T799800x1600250.225 
Illustration of Spatial Resolutions IPPC. Credits: Image courtesy of the IPCC (AR4 WG 1 Chapter 1 page 113 Fig. 1.4).

Finite Methods

As a comparative example here are some typical grids of the UKCA model (Hadley Centre version of the Unified Model at UK).

Climate Models used by UKCA

The UKCA model runs within the Hadley Centre version of the Unified Model. There are a number of different versions of this climate model at a number of resolutions which are used for UKCA development.

UM VersionModelHorizontal ResolutionVertical LevelsModel TopScheme Used
6.1HadGAM1aN48 (2.5°×3.75°)L60~84kmTropospheric Chemistry
6.1HadGAM2N48L60~84kmStratospheric Chemistry
6.6.4HadGEM2-ESN96L38~40kmHadley Centre Earth System Model
7.1HadGEM3-AN96 (1.25°×1.875°)L38~40kmTropospheric Chemistry
7.3HadGEM3-A r2.0N96L38~40kmTropospheric Chemistry
7.3HadGEM3-A r2.0N96L63~40kmTropospheric Chemistry
7.3HadGEM3-A r2.0N96L85  85kmStratospheric Chemistry
7.3HadGEM3-A r2.0N48L60~84kmStratospheric Chemistry
7.3HadGEM3-AO r2.0N48L60~84kmQUEST Earth System Model

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  1. Atmospheric Modelling, Data Assimilaton and Predictability, *Eugenia Kalnay, Cambridge University Press.