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