Solar Wind Discontinuities in the Outer Heliosphere: Spatial Distribution Between 1 and 5 AU

Abstract

Solar wind discontinuities (SWDs) are kinetic plasma structures that significantly contribute to the spectrum of magnetic field fluctuations and solar wind heating. Using Juno spacecraft data from 1 AU to 5 AU, combined with measurements from Wind, ARTEMIS, and STEREO at 1 AU, we disentangle spatial (radial) and temporal (solar activity) variations of SWD properties. We find that (a) the occurrence rate of SWDs decreases with radial distance from the Sun, following a $1/r$ relationship; (b) the SWD thickness increases with radial distance, but when normalized to the ion inertial length, the thickness remains almost unchanged within [1, 5]AU; (c) the SWD current density decreases with radial distance, but when normalized to the Alfvén current ($J_A=eN{V}_A$, where symbols have their usual definitions), the current density remains almost unchanged within [1, 5]AU; (d) the probability distributions of SWD normalized thickness and current density remain constant over time (in the 5 year period of Juno cruise phase) at 1 AU. We discuss these results in the context of theories of the origin and dynamics of SWDs.