Space Weather Forecasting: What We Know Now and What Are the Current and Future Challenges?

Geomagnetic storms are caused by solar wind southward magnetic fields that impinge upon the Earth's magnetosphere (Dungey, 1961). How can we forecast the occurrence of these interplanetary events? We view this as the most important challenge in Space Weather. We discuss the case for magnetic clouds (MCs), interplanetary sheaths upstream of ICMEs, corotating interaction regions (CIRs) and high speed streams (HSSs). The sheath- and CIR-related magnetic storms will be difficult to predict and will require better knowledge of the slow solar wind and modeling to solve. There are challenges for forecasting the fluences and spectra of solar energetic particles. This will require better knowledge of interplanetary shock properties from the Sun to 1 AU (and beyond), the upstream slow solar wind and energetic "seed" particles. Dayside aurora, triggering of nightside substorms, and formation of new radiation belts can all be caused by shock and interplanetary ram pressure impingements onto the Earth's magnetosphere. The acceleration and loss of relativistic magnetospheric "killer" electrons and penetrating electric fields in terms of causing positive and negative ionospheric storms are currently reasonable well understood, but refinements can still be made. The forecasting of extreme events (extreme shocks, extreme solar energetic particle events, and extreme geomagnetic storms ( "Carrington" events or greater)) are also discussed. Energetic particle precipitation and ozone destruction is briefly discussed. For many of the studies, the Parker Solar Probe, Solar Orbiter, Magnetospheric Multiscale Mission (MMS), Arase, and SWARM data will be useful. [ABSTRACT FROM AUTHOR]