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.

References in corpus (4)

• Alfven Wave Solar Model (AWSoM): Coronal Heating
• Radial evolution of the wave-vector anisotropy of solar wind turbulence between 0.3 and 1 AU
• Proton Heating in Solar Wind Compressible Turbulence with Collisions between Counter-propagating Waves
• Spectral Anisotropy of Elsässer Variables in Two Dimensional Wave-vector Space as Observed in the Fast Solar Wind Turbulence

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