Sunward-propagating Alfvénic Fluctuations Observed in the Heliosphere
Abstract
The mixture/interaction of anti-sunward-propagating Alfvénic fluctuations (AFs) and sunward-propagating Alfvénic fluctuations (SAFs) is believed to result in the decrease of the Alfvénicity of solar wind fluctuations with increasing heliocentric distance. However, SAFs are rarely observed at 1 au and solar wind AFs are found to be generally outward. Using the measurements from Voyager 2 and Wind, we perform a statistical survey of SAFs in the heliosphere inside 6 au. We first report two SAF events observed by Voyager 2. One is in the anti-sunward magnetic sector with a strong positive correlation between the fluctuations of magnetic field and solar wind velocity. The other one is in the sunward magnetic sector with a strong negative magnetic field—velocity correlation. Statistically, the percentage of SAFs increases gradually with heliocentric distance, from about 2.7% at 1.0 au to about 8.7% at 5.5 au. These results provide new clues for understanding the generation mechanism of SAFs.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2016
- DOI:
- 10.3847/2041-8205/824/1/L2
- arXiv:
- arXiv:1606.03308
- Bibcode:
- 2016ApJ...824L...2L
- Keywords:
-
- magnetic fields;
- magnetohydrodynamics: MHD;
- plasmas;
- solar wind;
- turbulence;
- waves;
- Physics - Space Physics
- E-Print:
- The Astrophysical Journal Letters, 824:L2 (6pp), 2016 June 10