A semi-empirical approach to simulating the <i>Dst</i> index in global MHD models of Earth’s magnetosphere

The <italic>Dst</italic> index has been commonly used to measure the geomagnetic effectiveness of magnetic storm events for several decades. Based on Burton’s empirical <italic>Dst</italic> model and the global magneto-hydrodynamic (MHD) simulation of Earth’s magnetosphere, here we proposed a semi-empirical model to forecast the <italic>Dst</italic> index during geomagnetic storms. In this model, the ring current contribution to the <italic>Dst</italic> index is derived from Burton’s model, while the contributions from other current systems are obtained from the global MHD simulation. In order to verify the model accuracy, a number of recent magnetic storm events are tested and the simulated <italic>Dst</italic> index is compared with the observation through the correlation coefficient (CC), prediction efficiency (PE), root mean square error (RMSE) and central root mean square error (CRMSE). The results indicate that, in the context of moderate and intense geomagnetic storm events, the semi-empirical model performs well in global MHD simulations, showing relatively higher CC and PE, and lower RMSE and CRMSE compared to those from the empirical model. Compared with the physics-based ring current models, this model inherits the advantage of fast processing from the empirical model, and easy implementation in a global MHD model of Earth’s magnetosphere. Therefore, it is suitable for the <italic>Dst</italic> estimation under a context of a global MHD simulation.