SUNWARD-PROPAGATING ALFVÉNIC FLUCTUATIONS OBSERVED IN THE HELIOSPHERE

• Main Authors: Li, Hui (Author), He, Jiansen (Author), Belcher, John Winston (Contributor), Wang, Chi 1967- (Author), Richardson, John D. (Author)
• Other Authors: Massachusetts Institute of Technology. Department of Physics (Contributor), MIT Kavli Institute for Astrophysics and Space Research (Contributor), Richardson, John D (Contributor)
• Format: Article
• Language: English
• Published: IOP Publishing, 2016-12-28T16:35:20Z.
• Subjects: Article
• Online Access: Get fulltext

 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.