Space Physics Seminar fall-2018

The transition from the outer solar corona to the inner heliosphere is, in several important senses, the last unexplored frontier of the solar system. It spans a gap in understanding that arises in part from the difficulty of both sampling (used to study the solar wind) and remote imaging (used to study the solar corona). Simultaneously, those two techniques have led to separate specialized scientific communities with their own jargon and modes of understanding. In recent years, image processing has developed enough to reveal global and cross-scale structure in the young solar wind; and the Parker Solar Probe is now on its way to sample this transition zone directly. These two converging developments promise a unified understanding of this last segment of the corona. I will present several recent results derived from careful post-processing of images from the STEREO coronagraphs and heliospheric imagers, and their implications for what Parker Solar Probe is likely to encounter. Important results include direct measurement of the onset of hydrodynamic turbulence in the solar wind; detection of a highly structured, inhomogeneous outer corona; of a gradual (rather than sudden) transition from coronal to solar wind dynamics; and of some enigmatic new phenomena near 10 Rs from the Sun. These results, together, point to a paradigm that is more nuanced and far more complex than current models imply, with unexpected and emergent cross-scale phenomena for PSP and future imagers to explore.