Cranmer, S. R. 1999, ``Acceleration of the High-Speed Solar Wind,'' in Physics of the Solar Corona and Transition Region, Monterey, California , 24-27 August 1999 (Invited Talk).


This talk will review the current state of understanding about how the steady-state, high-speed solar wind is accelerated from the base of the corona to its terminal speed of 600-800 km/s. Spectroscopic observations of the extended corona (in the primary acceleration region of 1-10 solar radii) from, e.g., SOHO and Spartan 201, continue to complement in situ spacecraft measurements (at distances greater than 0.3 AU). These observations present theorists with a large number of firm constraints that must be reproduced by models. Because the majority of the fast solar wind is a collisionless plasma, it is becoming evident that the energy and momentum of electrons, protons, and minor ions should be modeled independently. Also, since departures from isotropic Maxwellian velocity distributions are observed ubiquitously, simple fluid treatments of the solar wind need to be re-examined and compared with more complete kinetic models. A large number of physical mechanisms have been postulated to provide the outward acceleration of the solar wind, and this talk will attempt to classify and re-examine these processes in the light of the most current observations. Many acceleration mechanisms rely solely on coronal heating to generate a plasma pressure able to counteract gravity, but there are also several plausible sources of direct momentum deposition. In any case, it is clear that the dynamical state of the solar wind is intimately linked with the still-unknown mechanisms that transport subphotospheric convective energy above the transition region.

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