Semi-Analytic Spin-Up (SASU) of Coupled Carbon-Nitrogen Cycle Models

This chapter introduces the concept of spin-up in land biogeochemical models. Spin-up is a standard initialization procedure, which is commonly included in protocols of model intercomparison projects. Conventional spin-up, repeatedly running the model with recursive environmental forcing to achieve a steady state, is very time consuming. Semi-analytic spin-up (SASU) enabled by the matrix representation significantly improves the computational efficiency of spin-up for land biogeochemical models. The implementation of SASU in the Community Atmosphere and Biosphere Land Exchange (CABLE) model is demonstrated. The SASU method has been proven to save about 92.4% and 86.6%, respectively, of the computational time for spin-up of the global carbon-only and coupled carbon-nitrogen models.