A One-Sided Aspect of Alfvenic Fluctuations in the Solar Wind

Using Advanced Composition Explorer (ACE) 64 s data at 1 AU we find that Alfvénic fluctuations propagating outward from the Sun along the magnetic field, B, in the solar wind often produce one-sided variations in one of the equatorial components of B and velocity, V. This is a natural consequence of the fact that the Alfvénic fluctuations are transverse fluctuations in which |B| remains nearly constant. Thus, fluctuations in the field component that defines the underlying background field direction are always relative to a base value rather than to an average value. This suggests that conclusions derived from statistical analyses of fluctuations in the solar wind that assume the fluctuations in all field components are relative to average values need to be re-examined. We also find that discrete, sunward-propagating Alfvénic fluctuations or rotational discontinuities are extremely rare in the pristine solar wind; thus far we have identified such discrete events in ACE data only in association with events identified as magnetic reconnection exhausts and/or in association with backstreaming ions from reverse shocks, including Earth's bow shock.