REFLECTION OF ALFVEN WAVES IN THE SOLAR-WIND

We have revisited the problem of propagation of toroidal and linear Al fven waves formulated by Heinemann and Olbert (1980) to compare WKB an d non-WKB waves and their effects on the solar wind. They considered t wo solar wind models and showed that reflection is important for Alfve n waves with periods of the order of one day and longer and that non-W KB Alfven waves are no more effective in accelerating the solar wind t han WKB waves. There are several recently published papers that seem t o indicate that Alfven waves with periods of the order of several minu tes should be treated as non-WKB waves and that these non-WKB waves ex ert a stronger acceleration force than WKB waves. The purpose of this paper is to study the origin of these discrepancies by performing para metric studies of the behavior of the waves under a variety of differe nt conditions. In addition, we want to investigate two problems that h ave not been addressed by Heinemann and Olbert, namely, calculate the efficiency of Alfven wave reflection by using the reflection coefficie nt and identify the region of strongest wave reflection in different w ind models. To achieve these goals, we investigated the influence of t emperature, electron density distribution, wind velocity, and magnetic field strength on the waves. The obtained results clearly demonstrate that Alfven wave reflection is strongly model dependent and that the strongest reflection can be expected in models with the base temperatu res higher than 10(6) K and with the base densities lower than 7 x 10( 7) cm(-3). Ln these models as well as in the models with lower tempera tures and higher densities, Alfven waves with periods as short as seve ral minutes have negligible reflection so that they can be treated as WKB waves; however, for Alfven waves with periods of the order of one hour or longer reflection is significant, requiring a non-WKB treatmen t. We also show that non-WKB, Linear Alfven waves are always less effe ctive in accelerating the plasma than WKB Alfven waves. Finally, it is evident from our results that the region of strongest wave reflection is usually located at the base of the models and hence that interpret ation of wave reflection based solely on the reflection coefficient ca n be misleading.