A Review of Alfvenic Turbulence in High-Speed Solar Wind Streams: Hints From Cometary Plasma Turbulence

Solar wind turbulence within high-speed streams is reviewed from the point of view of embedded single nonlinear Alfven wave cycles, discontinuities, magnetic decreases (MDs), and shocks. For comparison and guidance, cometary plasma turbulence is also briefly reviewed. It is demonstrated that cometary nonlinear magnetosonic waves phase-steepen, with a right-hand circular polarized foreshortened front and an elongated, compressive trailing edge. The former part is a form of wave breaking and the latter that of period doubling. Interplanetary nonlinear Alfven waves, which are arc polarized, have a similar to 180 degrees foreshortened front and with an elongated trailing edge. Alfven waves have polarizations different from those of cometary magnetosonic waves, indicating that helicity is a durable feature of plasma turbulence. Interplanetary Alfven waves are noted to be spherical waves, suggesting the possibility of additional local generation. They kinetically dissipate, forming MDs, indicating that the solar wind is partially compressive and static. The similar to 2 MeV protons can nonresonantly interact with MDs leading to rapid cross-field (similar to 5.5% Bohm) diffusion. The possibility of local (similar to 1 AU) generation of Alfven waves may make it difficult to forecast High-Intensity, Long-Duration AE Activity and relativistic magnetospheric electrons with great accuracy. The future Solar Orbiter and Solar Probe Plus missions should be able to not only test these ideas but to also extend our knowledge of plasma turbulence evolution. Plain Language Summary Interplanetary Alfvenic turbulence is studied from an observational microstructural viewpoint. We use cometary turbulence as a guide and for comparison to interplanetary turbulence. It is shown that single wave cycles reveal much of the ongoing physics. Alfven waves phase-steepen forming a high-frequency end, leaving a low-frequency end. This is a form of wave breaking and period doubling occurring at the same time. If Alfven waves occur at all scale sizes, this can explain the Kolmogrov-type spectra found in all studies. The interplanetary medium is also highly compressive. This is caused by the magnetic decreases detected at the ends of the Alfven waves. It is thought that this is a kinetic process associated with the dissipation of the Alfven waves. The interplanetary Alfven waves are often arc-polarized spherical waves implying a local source of generation. Some theoretical mechanisms for local generation are cited. Finally, it is shown that the MDs can cause rapid cross-field diffusion of energetic solar flare particles, perhaps explaining their broad distributions in solar longitude. Single cycle Alfven waves impinging on the magnetosphere cause strong and continuous auroral activity.