Non-Parker Spiral Interplanetary Magnetic Field Configurations Observed in Near-Earth Space: Statistical Features of Their Occurrence and Solar Wind Conditions

Abstract In near-Earth space, the interplanetary magnetic field (IMF) is generally characterized by the Parker spiral configuration with a spiral angle of approximately 45° clockwise from the radial axis of the Sun. However, spacecraft observations reveal that IMF lines can exhibit non-Parker spiral configurations with either a nearly radial (outward–inward), tangential (westward–eastward), or normal (northward–southward) direction defined in radial–tangential–normal coordinates on even hourly timescales. Using the IMF and solar wind data measured by the Wind spacecraft for the period 1995–2023, we present distinctive features in the occurrence and various solar wind parameters between these non-Parker spiral IMF configuration types. Our study reveals that (1) the occurrence of non-Parker spiral IMF configuration types has the Hale cycle (∼22 yr magnetic dynamo cycle) variations with their own phases depending on the sign of the major IMF components, (2) the solar wind in the radial/tangential IMF structure is deflected eastward/westward, which corresponds to the direction opposite to/same as the rotation direction of the Sun on the plane perpendicular to the line of sight, and (3) these IMF configuration types can be characterized by magnetic field topology, which is open (for radial IMF and tangential IMF) or closed (for normal IMF). Our findings therefore provide insights into the formation mechanisms of these non-Parker spiral IMF configurations observed in near-Earth space. Moreover, our results suggest that spacecraft missions to various areas in interplanetary space are needed to better understand spatiotemporal evolutions of the solar-originated magnetic field structure in the heliosphere.