Origins of the Ambient Solar Wind: Implications for Space Weather

TL;DR

This paper reviews current understanding of coronal heating and solar wind acceleration, highlighting progress and challenges in predicting space weather impacts from solar wind variations.

Contribution

It synthesizes recent advances in observations, modeling, and forecasting techniques for the origins of the solar wind and their implications for space weather prediction.

Findings

Fast solar wind linked to large coronal holes

Slow wind sources include streamers, pseudostreamers, and active regions

Progress in modeling and data analysis offers hope for better understanding

Abstract

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.