GO5.0: the joint NERC–Met Office NEMO global ocean model for use in coupled and forced applications

A Megann,S Alderson,J Siddorn,D Storkey,Y Aksenov,D Calvert,P Hyder,T Graham,B Sinha

doi:10.5194/gmd-7-1069-2014

A Megann, S Alderson + Show 7 more

Open Access

https://doi.org/10.5194/gmd-7-1069-2014

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Abstract

Abstract. We describe a new Global Ocean standard configuration (GO5.0) at eddy-permitting resolution, developed jointly between the National Oceanography Centre and the Met Office as part of the Joint Ocean Modelling Programme (JOMP), a working group of the UK's National Centre for Ocean Forecasting (NCOF) and part of the Joint Weather and Climate Research Programme (JWCRP). The configuration has been developed with the seamless approach to modelling in mind for ocean modelling across timescales and for a range of applications, from short-range ocean forecasting through seasonal forecasting to climate predictions as well as research use. The configuration has been coupled with sea ice (GSI5.0), atmosphere (GA5.0), and land-surface (GL5.0) configurations to form a standard coupled global model (GC1). The GO5.0 model will become the basis for the ocean model component of the Forecasting Ocean Assimilation Model, which provides forced short-range forecasting services. The GC1 or future releases of it will be used in coupled short-range ocean forecasting, seasonal forecasting, decadal prediction and for climate prediction as part of the UK Earth System Model. A 30-year integration of GO5.0, run with CORE2 (Common Ocean-ice Reference Experiments) surface forcing from 1976 to 2005, is described, and the performance of the model in the final 10 years of the integration is evaluated against observations and against a comparable integration of an existing standard configuration, GO1. An additional set of 10-year sensitivity studies, carried out to attribute changes in the model performance to individual changes in the model physics, is also analysed. GO5.0 is found to have substantially reduced subsurface drift above the depth of the thermocline relative to GO1, and also shows a significant improvement in the representation of the annual cycle of surface temperature and mixed layer depth.

Highlights

Coupled climate models developed at the UK Met Office have been at the forefront of international climate research and projections for the past 15 years
The main physics change between GO1 and GO5.0 is a set of changes to the vertical mixing parameters based on the work of Calvert and Siddorn (2013)
The NEMO implementation of the scheme includes a number of parameterisations to represent additional unresolved turbulent processes, including surface wave breaking (Craig and Banner, 1994) and Langmuir turbulence (Axell, 2002)

Summary

Introduction

Coupled climate models developed at the UK Met Office have been at the forefront of international climate research and projections for the past 15 years. HadCM3 (Hadley Centre Coupled Model version 3; Gordon et al, 2000) was used in the Third and Fourth Assessment Reports (Houghton et al, 2001; Solomon et al, 2007) and is still widely used as a standard tool in climate research, while HadGEM1 (Hadley Centre Global Environmental Model version 1) (Johns et al, 2006), HadGEM2 (Collins et al, 2008) and HadGEM3 (Hewitt et al, 2011) have offered improvements in resolution, numerics and physics All these models have an ocean on a horizontal grid of around 1◦, the HadGEM models have a refinement of the north–south grid scale close to the Equator down to 1/3◦. At the Met Office and elsewhere there is increasing interest in using a seamless modelling system for use at all timescales from short range forecasting to climate prediction (Brown et al, 2012)

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