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UKESM newsletter 1 - August 2015

Development of the 1st version of the UK Earth system model

The UK Earth system modelling project is a joint venture between the Met Office Hadley Centre (MOHC) and the Natural Environmental Research Council (NERC) to develop and apply future UK Earth system models. This article describes the main components of the first version of UKESM (UKESM1), currently under development and discusses some of the motivation for developing both a high and low resolution version of the model.

A low resolution version of UKESM1

Two versions of UKESM1 are under development, differing in the horizontal resolutions used in both the atmosphere and ocean. This article describes work performed to recommend a resolution for the low resolution version of UKESM1 (UKESM1-lr). Science performance results and a number of computational and technical arguments are presented to motivate UKESM1-lr employing a resolution of N96 (~140km) in the atmosphere and 1° in the ocean.

A fully detailed report (PDF, 6MB) on this work is also available.

Reduced-resolution chemistry and aerosols within UKESM1

UKESM1 includes an advanced representation of atmospheric trace gas chemistry and aerosols (UKCA-GLOMAP) which significantly increases the computational cost of UKESM1. In order to retain the high resolution of UKESM1-hr for physical climate processes, while also retaining the advanced process complexity of UKCA-GLOMAP, we are working to develop a hybrid resolution version of UKESM1-hr. In this configuration the physical model core of UKESM1 (HadGEM3) will run at a resolution of N216 (~60km) while UKCA-GLOMAP will be interactively run at a coarser resolution (e.g. N96).

Simplified aerosol chemistry in UKCA

For UKESM1 we have developed a minimal chemistry configuration within UKCA to support the GLOMAP-mode aerosol scheme without the full cost of more complete tropospheric-stratosperic chemistry. This chemistry configuration will be employed by the HadGEM3 physical climate model to enable it to use the same aerosol setup as UKESM, and will increase the consistency between the physical and Earth system models.