Abstract
Abstract. FORTE 2.0 is an intermediate-resolution coupled atmosphere–ocean general circulation model (AOGCM) consisting of the Intermediate General Circulation Model 4 (IGCM4), a T42 spectral atmosphere with 35σ layers, coupled to Modular Ocean Model – Array (MOMA), a 2∘ × 2∘ ocean with 15 z-layer depth levels. Sea ice is represented by a simple flux barrier. Both the atmosphere and ocean components are coded in Fortran. It is capable of producing a stable climate for long integrations without the need for flux adjustments. One flexibility afforded by the IGCM4 atmosphere is the ability to configure the atmosphere with either 35σ layers (troposphere and stratosphere) or 20σ layers (troposphere only). This enables experimental designs for exploring the roles of the troposphere and stratosphere, and the faster integration of the 20σ layer configuration enables longer duration studies on modest hardware. A description of FORTE 2.0 is given, followed by the analysis of two 2000-year control integrations, one using the 35σ configuration of IGCM4 and one using the 20σ configuration.
Highlights
Numerical models of the coupled climate system are important tools for studying the Earth’s climate
FORTE 2.0 is a global coupled atmosphere–ocean general circulation model consisting of a 2◦ resolution configuration of the MOMA (Modular Ocean Model – Array) (Webb, 1996) ocean model coupled to a T42 configuration of the Intermediate General Circulation Model 4 (IGCM4) (Joshi et al, 2015) atmosphere model
The weaker Atlantic Meridional Overturning Circulation (AMOC) in L20 is consistent with the cooling and freshening trends seen at depth, since a weaker AMOC allows a greater influence of Antarctic Bottom Water (AABW) in the abyssal ocean
Summary
Numerical models of the coupled (atmosphere–ocean) climate system are important tools for studying the Earth’s climate. They provide insight into phenomena which are difficult to observe directly, such as the Atlantic Meridional Overturning Circulation (AMOC) or the effects of increasing atmospheric CO2. Sinha and Smith (2002) developed FORTE (Fast Ocean Rapid Troposphere Experiment), a fast and flexible coupled climate model, for the purposes of climate studies. This paper describes the coupled model and its components and demonstrates that FORTE 2.0 produces a realistic and stable climate without the need for flux adjustments. The rest of this paper is organised as follows: Sect. 2 gives a description of FORTE 2.0; Sect. 3 presents the model spinup; Sect. 4 presents the control climate; Sect. 5 discusses the main modes of climate variability in the model; Sect. 6 concludes the paper
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