Inherent length scales of periodic mesoscale density structures in the
solar wind over two solar cycles
Abstract
It is now well-established through multiple event and statistical
studies that the solar wind at 1 AU contains contains periodic,
mesoscale (L~100-1000 Mm) structures in the proton
density. Composition variations observed at 1 AU within periodic density
structures and remote sensing observations of similar structures in the
young solar wind indicate that at least some of these periodic
structures originate in the solar atmosphere as a part of solar wind
formation. Viall [2008] analyzed 11 years of data from the Wind
spacecraft near L1 and demonstrated a recurrence to the length scales of
periodic structures in the solar wind proton density observed, and a
potential solar cycle dependence. In the time since that study, Wind has
collected 14 additional years of solar wind data, allowing a more
thorough examination of the dependence of these structures as a function
of solar cycle. In addition, the Wind plasma data have been reprocessed
in the interim, and new methods for spectral background approximation
have been developed, allowing a reevaluation of the precision and
accuracy of the initial study. In this study, we analyze 25 years of
Wind data collected near L1, and produce occurrence distributions of
statistically significant periodic length scales in proton density. The
results confirm the Viall [2008] study and significantly extend
those results to show a solar cycle dependence of the length scales, and
a possible relation to solar “termination” events.