Abstract Flux transfer events (FTEs) transport solar wind energy and plasma into the Earth's magnetosphere. Their topological twisting features can be described by magnetic helicity, a crucial quantity for understanding the large‐scale magnetic field structure and evolution. The interplanetary magnetic field (IMF) orientation significantly influences the properties and global behaviors of FTEs. Recent observations revealed the relation between FTE formation and helicity sign and its dependence on IMF orientations. However, the detailed characteristics of FTE helicity magnitude and its relations with FTE evolution as influenced by IMF orientation are still poorly understood. Using global MHD simulations with different IMF clock angles arctan( B y / B z ), we designed a novel method to calculate FTE helicity magnitude for the first time and investigated its relations with other FTE properties. We find that magnetic helicity has positive correlations with the FTE core field and lifetime. The helicity and lifetime are the largest when IMF has comparable B y and B z , implying that as IMF turns from near‐purely southward to duskward, the helicity and lifetime first increase as a function of increasing B y / B z but then decrease once B y / B z exceeds a threshold. This is attributed to the increasing magnetic tension force generated by the FTE core field, which can suppress kink instability or straighten the flux rope depending on the IMF orientation regime. Interplanetary magnetic field B y generally controls FTE helicity signs, with exceptions occurring when IMF B y is small even without the Hall effect. These findings enhance our understanding of global‐scale FTE structures and evolution, aiding interpretation of future satellite data such as SMILE and TRACERS.
Bai et al. (2026) studied this question.