Understanding the Interplanetary Origin of Space Weather and Why this is Essential for Successful Forecasting

Abstract:

Even before the space era and the discovery of the solar wind, there was clear evidence that the Sun was a major driver of space weather, and that this influence was somehow propagated to the Earth perhaps by long-lived “corpuscular streams” corotating with the Sun or by mass ejections that entrained the solar magnetic field. It is now well-established (e.g., Zhang et al. (2007), JGR 112, A10102, doi:10.1029/2007JA012321) that structures in the solar wind modulate the intensity of space weather including geomagnetic storms. In particular, the passage of interplanetary coronal mass ejections and the associated upstream sheaths drives ~90% of intense storms with Dst < -100 nT, the remainder of these storms being associated with corotating interaction regions/high speed streams. Furthermore, the detailed time variations of the plasma and magnetic field within these structures, in particular the southward magnetic field component, determine the development of the activity. Thus, acquiring knowledge of the solar wind structures approaching Earth and of the plasma and magnetic conditions within these structures is vital to the successful forecasting of space weather. We discuss the ways in which this knowledge may be acquired (e.g., from solar observations including coronagraphs, in situ solar wind observations, and modeling), and the current limitations that impact successful forecasting.