Abstract
Abstract. Modeling atmospheric chemistry at fine resolution globally is computationally expensive; the capability to focus on specific geographic regions using a multiscale grid is desirable. Here, we develop, validate, and demonstrate stretched grids in the GEOS-Chem atmospheric chemistry model in its high-performance implementation (GCHP). These multiscale grids are specified at runtime by four parameters that offer users nimble control of the region that is refined and the resolution of the refinement. We validate the stretched-grid simulation versus global cubed-sphere simulations. We demonstrate the operation and flexibility of stretched-grid simulations with two case studies that compare simulated tropospheric NO2 column densities from stretched-grid and cubed-sphere simulations to retrieved column densities from the TROPOspheric Monitoring Instrument (TROPOMI). The first case study uses a stretched grid with a broad refinement covering the contiguous US to produce simulated columns that perform similarly to a C180 (∼ 50 km) cubed-sphere simulation at less than one-ninth the computational expense. The second case study experiments with a large stretch factor for a global stretched-grid simulation with a highly localized refinement with ∼10 km resolution for California. We find that the refinement improves spatial agreement with TROPOMI columns compared to a C90 cubed-sphere simulation of comparable computational demands. Overall, we find that stretched grids in GEOS-Chem are a practical tool for fine-resolution regional- or continental-scale simulations of atmospheric chemistry. Stretched grids are available in GEOS-Chem version 13.0.0.
Highlights
Global simulations of atmospheric chemistry are computationally demanding
Eastham et al (2018) developed the capability for Goddard Earth Observing System (GEOS)-Chem to operate on cubed-sphere grids in a distributed memory framework for massive parallelization and to use the Model Analysis and Prediction Layer (MAPL; Suarez et al, 2007) of the NASA Global Modeling and Assimilation Office (GMAO) together with the Earth System Modeling Framework (ESMF; Hill et al, 2004) to couple model components
Fine-resolution simulations of atmospheric chemistry are necessary to capture fine-scale modes of variability such as localized sources, nonlinear chemistry, and boundary layer processes, but fine-resolution simulations have been impeded by computational expense
Summary
Global simulations of atmospheric chemistry are computationally demanding. Chemical mechanisms in the troposphere typically involve more than 100 chemical species, emitted by anthropogenic and natural sources, with production and loss by chemical reactions, and mixing through 3-D transport on all scales. We implement grid refinement in GCHP using a technique that stretches the model grid to enhance its resolution in a user-defined region, enabling massively parallel global multiscale simulations of atmospheric chemistry. Eastham et al (2018) developed the capability for GEOS-Chem to operate on cubed-sphere grids in a distributed memory framework for massive parallelization and to use the Model Analysis and Prediction Layer (MAPL; Suarez et al, 2007) of the NASA Global Modeling and Assimilation Office (GMAO) together with the Earth System Modeling Framework (ESMF; Hill et al, 2004) to couple model components.
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