The Role of Alfv\`en Waves in Solar Wind Acceleration

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Session 92 -- Solar Active Regions and Solar Wind
Oral presentation, Wednesday, 11, 1995, 10:00am - 11:30am

[92.06] The Role of Alfv\`en Waves in Solar Wind Acceleration

M. Krogulec (UAH \& Uni. Gda\'nsk, Poland), Z. E. Musielak (UAH), S. T. Suess, S. F. Nerney, R. L. Moore (NASA/MSFC)

The fact that Alfv\'en waves may play a significant role in the energy balance in solar coronal holes has been known for a number of years. A special attention has been given to these waves because they can transfer energy to large distances and deposit efficiently momentum in the background medium. It has been shown that non-WKB effects are important for Alfv\'en waves with periods of the order of one day and longer, and that non-WKB Alfv\'en waves are no more effective in acceleration of the solar wind than WKB waves. There are, however, some recently published papers which seem to indicate that Alfv\'en waves with periods of the order of several minutes should be treated as non-WKB waves and that these waves exert a stronger acceleration force than WKB waves. To investigate the origin of these discrepancies, we have performed a series of parametric studies of the behavior of the waves under a variety of different conditions in solar coronal holes. The obtained results demonstrate that both Alfv\'en wave reflection and the acceleration force due to the waves are strongly model dependent. The strongest reflection can be expected in models with the base temperatures higher than $10^6$ K and with the base densities lower than $7 \times 10^7$$ cm^{-3}$. However, the strongest acceleration force is expected in the models with the weakest reflection. This clearly indicates that linear non-WKB Alfv\'en waves are always less effective in accelerating the plasma than WKB Alfv\'en waves. Implications of this result for the heating in solar coronal holes and for the acceleration of the solar wind will be discussed.

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