Comparison of small-scale flux rope magnetic properties to large-scale magnetic clouds: Evidence for reconnection across the HCS

摘要

A newly developed semi-automated routine to identify small-scale symmetric force-free flux ropes in the solar wind was used to search 11 years (1995–2005) of WIND magnetic field data. We identified 68 flux ropes whose durations range from 39 minutes up to 12.2 hours, with the distribution strongly peaked at an hour or less. These small-scale flux ropes have strong core field signatures in total magnetic field coincident with bipolar field inflection consistent with a cylindrically symmetric flux rope model. They are predominately observed in the slow and moderate solar wind (<500 km s?1). They are observed to have a solar cycle occurrence variation with most small-scale flux rope events found during solar minimum. This database of small-scale flux ropes is compared to previously published small-scale flux rope surveys and interplanetary coronal mass ejection (ICME)/magnetic cloud databases. The size distribution of flux ropes in the solar wind appears to be bimodal, with the majority of events having durations 4 hours or less where the magnetic cloud distribution peaks between 12 and 16 hours. The results suggest different source mechanisms for small and large-scale flux ropes.