Ionospheric reflection of small-scale Alfven waves

The transfer of energy from the magnetosphere to the ionosphere occurs thro ugh complex mechanisms that often involve shear Alfven waves, implying that the interaction of these waves with the ionosphere is fundamental to our u nderstanding of the coupling process. Indeed, a variety of problems that in volve magnetosphere-ionosphere coupling assume that the ionosphere acts as a perfectly reflecting boundary, although we know that this is not the case in general. In this work, we calculate the reflection coefficient of shear Alfven waves incident on the ionosphere under three different ionospheric profiles. Our results indicate that 1) under all profiles considered, refle ction of shear Alfven waves with perpendicular lengths of similar to 1 km o r less is negligible and 2) under a profile that might be typical of a nigh tside ionosphere, reflection of shear Alfven waves is significant only for waves with frequencies below similar to 0.4 Hz and lambda (x) above similar to 2 km; reflection of waves with lambda (x) less than similar to 2 km is poor.