Cranmer, S. R., and Esser, R. 2001, ``Cyclotron Resonance of Ions in the Solar Corona: Observations and Models,'' IAGA-IASPEI Joint Scientific Assembly, Hanoi, Vietnam, Session G4.04: The 3D Corona and Solar Wind, 24 August 2001 (Invited Talk).


This presentation reviews the current state of understanding ion heating and acceleration in the extended solar corona. Observations with the UVCS instrument on SOHO, coupled with interplanetary particle measurements going back several decades, put strong constraints on explanations of how ions receive their larger-than-expected temperatures and outflow speeds. The most promising mechanism for heating and accelerating heavy ions remains the dissipation of high-frequency (10 to 10,000 Hz) ion cyclotron waves. Heating the protons, on the other hand, is a more open question. The physics of the ion cyclotron interaction in the corona has only begun to be explored in detail, and we will discuss recent insights into the generation and damping of these waves. The characteristic non-Maxwellian ion velocity distributions that arise from the dissipation of parallel-propagating electromagnetic waves will be presented. It will be shown how future ultraviolet spectroscopy can be extended to detect: (1) possible unique identifiers of these non-Maxwellian distributions, and (2) preferential heating effects that could help specify the relative amounts of damping, turbulent cascade, and local plasma instability in the corona.

Measurements of ion charge states in the solar wind have been known to be sensitive probes of the coronal plasma conditions, primarily the electron velocity distribution function and differential flow speeds between ions. It is hoped that the combination of ultraviolet spectroscopy and nonequilibrium ionization models can provide a vastly increased set of empirical constraints on the theory of coronal heating and solar wind acceleration.

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