Linking long-term switchback variability at 1 au to solar-surface mechanisms: A 27-year statistical study

Context. Switchbacks–transient, large-angle deflections of the interplanetary magnetic field–pervade the solar wind, yet their origin remains disputed. Current ex situ theories, notably coronal jets and interchange reconnection, are typically tested on day-scale intervals. Aims. We aim to establish a connection between switchbacks and ex situ theories on solar-cycle timescales. Methods. We exploited 27 years of continuous in situ measurements from ACE, Wind, and STEREO-A/B at 1 au, complemented by synoptic remote-sensing data from SDO, to examine the solar-cycle modulation of switchback occurrence and to test whether ex situ scenarios (coronal jets and interchange reconnection) play a dominant role in such long-term modulation. Results. The switchback occurrence rate correlates strongly with Alfvénicity (cc = 0.70 ± 0.04) and shows no solar-maximum preference (independent of the sunspot number, cc = 0.13 ± 0.05). Coronal jets affect switchbacks only indirectly via modulation of the solar wind speed. Multi-spacecraft consensus confirms that a stable, Alfvénicity-dependent process governs switchback variability, rather than episodic surface drivers. In addition, these results are robust to the deflection threshold of switchbacks. These findings impose quantitative constraints on theories of solar-wind turbulence and the transport of magnetic energy from the Sun to interplanetary space.