Occurrence and Evolution of Switchbacks in the Inner Heliosphere: Parker Solar Probe Observations

Abstract

Since its launch in 2018, the Parker Solar Probe (PSP) mission revealed the presence of numerous fascinating phenomena occurring closer to the Sun, such as the presence of ubiquitous switchbacks (SBs). The SBs are large magnetic field deflections of the local magnetic field relative to a background field. We investigated the statistical properties of the SBs during the first 10 encounters between 13.28 and 58 solar radii ( R _⊙ ) using data from the SWEAP and FIELDS suites on board PSP. We find that the occurrence percentage of small deflections with respect to the Parker spiral decreases with radial distance ( R ). In contrast, the occurrence percentage of the large deflections (SBs) increases with R , as does the SB patches. We also find that the occurrence of SBs correlates with the bulk velocity of the solar wind, i.e., the higher the solar wind velocity, the higher the SB occurrence. For V _sw ≤ 400 km s ^−1 , the SB occurrence percentage shows a constantly increasing trend between 13 and 58 R _⊙ . However, for V _sw > 400 km s ^−1 , the occurrence percentage saturates beyond 35 R _⊙ . The occurrence percentage of mini SB patches (200 s) increases with R . Sub-Alfvénic regions that we analyzed during Encounters 8–10 have not shown any SBs. This analysis of the PSP data hints that some of the SBs are decaying and some are being created in situ.

Keywords

• Solar wind
• Interplanetary magnetic fields