Collaborative Research: From Adjoints for the Few to Adjoints for the Many: Integrating the Use of Adjoint Methods in Earth System Modeling

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Adjoint models are useful mathematical tools for studies that require state estimates (e.g. forecasts or projections), and sensitivities of model output with respect to model input. Adjoint methods allow efficient and comprehensive computation of model sensitivity to very high dimensional spaces of inputs. An adjoint model can be used to efficiently quantify the effects of changes in the spatio-temporal distribution of surface winds, buoyancy fluxes, or mixing distribution in the ocean, on quantities such as carbon uptake in the Southern Ocean. Developing adjoint models for given state-of-the-art geophysical models can be as complex as developing the geophysical models themselves, which is one reason why adjoints are not frequently used. This project will advance the tools needed to implement adjoint models.The project will pursue three inter-related work packages to overcome these limitations:(1) bringing the open-source AD tool OpenAD to full maturity on four open-source Earth system modeling frameworks used in climate research and education(2) developing configurations around several science applications where the sensitivity of quantities of interest (cost functions) to inputs (control variables) can be configured for realistic runtimes,(3) developing a generic Message Passing Interface (MPI)-based framework to enable the coupling between high-resolution forward and low-resolution adjoint models. The proposed geoscience studies will be of interest to computational and climate scientists. A broader impact of this research will be to enable adjoint methods to be more easily used across the geosciences, with potential to be transformative for data assimilation and sensitivity analysis in a wide range of geoscience and other disciplines.