The GUMICS-4 global MHD magnetosphere-ionosphere coupling simulation

► GUMICS is a widely used global MHD code for Earth's magnetosphere. ► We review GUMICS development history, design and technical features. ► GUMICS agrees with observations on magnetopause distance, tail IMF penetration, etc. ► GUMICS predicts the spatiotemporal behaviour of the magnetosphere to a useful extent.