Characterization of Small Flux Ropes Using Juno Spacecraft Cruise-phase Data

Abstract

In this study, we utilize magnetic field data from the Juno mission’s cruise phase to visually identify and analyze 338 interplanetary small flux ropes (SFRs) across a heliocentric distance range of 1–5.5 au. The events are uniformly distributed across heliocentric distances, showing no clear trend. Through superposed epoch analysis, we find that the average SFR magnetic field profiles are symmetric and show little variation across the observed heliocentric distances. Additionally, we observe a slight increasing trend in the mean duration of SFRs, indicating minimal expansion during propagation. Furthermore, we determine that the SFR mean magnetic field dependence on distance is best fit by two separate power laws, exhibiting a steeper decay from 1 to ∼2.1 au and a shallower decay from ∼2.1 to 5.5 au. Near 1 au, the statistical decay rate of the mean magnetic field magnitude of SFRs is slightly higher than that of the interplanetary magnetic field (IMF), suggesting that SFRs may become indistinguishable from the IMF over time. This finding implies that SFRs detected at greater radial distances are possibly generated in situ as opposed to near the Sun. However, only ∼26% of the total population of SFRs in our catalog occurs within 1 day from the heliospheric current sheet (HCS), indicating a very limited association between the occurrence of the majority of SFRs and the presence of the HCS. These results raise questions about the origin of SFRs detected at larger distances, encouraging further exploration for alternatives to the conventional generation mechanisms.