Solar wind Alfvénic turbulence: overcoming an old paradigm
Abstract
Despite many decades of studies, solar wind turbulence remains an open, unsolved problem in space plasma physics. The solar wind turbulent behavior is in many instances dominated by the nonlinear interaction between inward and outward propagating Alfvén waves, especially so-called Alfvénic turbulence, that displays a high degree of v-b correlations (and almost constant number density and magnetic field magnitude). Also, Alfvénic turbulence is especially prominent in fast solar wind streams. Such characteristics have strong implications for spectral features and has motivated the turbulent community to take a particular care of data selection, separating the streams according to their speed. However, recent results have shown that the slow-fast dichotomy should be overcome. Indeed, it has been found that even slow wind can be sometimes characterized by highly Alfvénic and high-amplitude fluctuations similar to that of the fast wind. Although the first observation of this kind of wind dates back to Helios data at the perihelion passage, L1 measurements during solar maximum revealed, quite unexpectedly, a statistically significant occurrence of this kind of wind.
On the other hand, recent observations by Parker Solar Probe (PSP) show the occurrence of Alfvénic slow wind at all the perihelion passages, putting this topic in the spotlight. In this talk, we review the main characteristics of the Alfvénic slow wind from L1 back to PSP closest approach, with a particular focus on the comparison with the fast wind and the standard slow wind. The several similarities between the two Alfvénic winds (fast and slow) suggest a similar origin, with the slow one coming from a low latitude small coronal hole, with a major role attributed to the super-radial expansion responsible for the lower velocity of the slow wind. This interpretation was confirmed by PSP observations. The upcoming Solar Orbiter data will be of further support in characterizing this kind of slow wind and in following the radial evolution of Alfvénicity in the inner heliosphere.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMSH033..01D
- Keywords:
-
- 2164 Solar wind plasma;
- INTERPLANETARY PHYSICS;
- 2169 Solar wind sources;
- INTERPLANETARY PHYSICS;
- 7509 Corona;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7524 Magnetic fields;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY