Editing HadCM3 (section)

== Atmosphere model (HadAM3) ==
[[File:Hadcm3-jja-djf-zonal-mean-t.png|thumb|right|Zonal mean temperatures in JJA (top) and DJF (bottom)]]

HadAM3 is a grid point model that has a horizontal resolution of 3.75 × 2.5 degrees in longitude × latitude. This corresponds to a spacing between points of approximately 300&nbsp;km and is roughly comparable to T42 truncation in a [[Gaussian grid|spectral model]]. There are 96 × 73 grid points on the scalar (pressure, temperature and moisture) grid; the vector (wind velocity) grid is offset by 1/2 a grid box (see [[Arakawa B-grid]]).<ref>{{cite web |url=http://cera-www.dkrz.de/IPCC_DDC/IS92a/HadleyCM3/Readme.hadcm3.grid |title=Archived copy |website=cera-www.dkrz.de |access-date=13 January 2022 |archive-url=https://web.archive.org/web/20030924195318/http://cera-www.dkrz.de/IPCC_DDC/IS92a/HadleyCM3/Readme.hadcm3.grid |archive-date=24 September 2003 |url-status=dead}}</ref> There are 19 levels in the vertical using a hybrid (sigma and pressure) coordinate system.

The timestep is 30&nbsp;minutes (with three sub-timesteps per timestep in the dynamics).  Near [[Polar regions of Earth|the poles]], fields are fourier-filtered to prevent instabilities due to the [[Courant–Friedrichs–Lévy condition|CFL]] criterion.

This is the model behind [[PRECIS]] (Providing Regional Climates for Impacts Studies) as well as being the atmosphere component of the [[distributed computing]] project [[Climateprediction.net]].