Cranmer, S. R. 2008, "Modeling the solar wind: A survey of theoretical ideas for the origins of fast and slow streams," HELIOS-2008: The Second Heliospheric Network Workshop, Kefalonia, Greece, May 6-9, 2008 (Invited Talk). [see also the Powerpoint slides (4.9 MB)]
Nearly a half-century has gone by since the discovery that the solar wind at 1 AU seems to exist in two relatively distinct states: slow and fast. There is still no universal agreement, though, concerning the primary physical cause of the observed range of plasma conditions, even in its simplest manifestation at solar minimum. It is still unknown whether the solar wind is fed by flux tubes that remain open (and are energized by footpoint-driven wavelike fluctuations) or if mass and energy is input more intermittently from closed loops into the open-field regions. In this presentation, I attempt to give a broad overview of the above issues and illustrate recent progress toward identifying the dominant physical processes. Specifically, I will present a summary of theoretical modeling efforts that seem to succeed in explaining the time-steady properties of the corona (and the fast and slow solar wind) in terms of an anisotropic MHD cascade driven by the partial reflection of low-frequency Alfven waves propagating along the superradially expanding solar magnetic field. Finally, I will outline the types of future observations that would be most able to test and refine these ideas.
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