Automated Detection of Small-scale Magnetic Flux Ropes in the Solar Wind: First Results from the Wind Spacecraft Measurements

Abstract

Abstract We have developed a new automated small-scale magnetic flux rope (SSMFR) detection algorithm based on the Grad–Shafranov (GS) reconstruction technique. We have applied this detection algorithm to the Wind spacecraft in situ measurements during 1996–2016, covering two solar cycles, and successfully detected a total number of 74,241 small-scale magnetic flux rope events with duration from 9 to 361 minutes. This large number of small-scale magnetic flux ropes has not been discovered by any other previous studies through this unique approach. We perform statistical analysis of the small-scale magnetic flux rope events based on our newly developed database, and summarize the main findings as follows. (1) The occurrence of small-scale flux ropes has strong solar-cycle dependency with a rate of a few hundred per month on average. (2) The small-scale magnetic flux ropes in the ecliptic plane tend to align along the Parker spiral. (3) In low-speed (<400 km s−1) solar wind, the flux ropes tend to have lower proton temperature and higher proton number density, while in high-speed (≥400 km s−1) solar wind, they tend to have higher proton temperature and lower proton number density. (4) Both the duration and scale size distributions of the small-scale magnetic flux ropes obey a power law. (5) The waiting time distribution of small-scale magnetic flux ropes can be fitted by an exponential function (for shorter waiting times) and a power-law function (for longer waiting times). (6) The wall-to-wall time distribution obeys double power laws with the break point at 60 minutes (corresponding to the correlation length). (7) The small-scale magnetic flux ropes tend to accumulate near the heliospheric current sheet (HCS). The entire database is available at http://fluxrope.info and in machine-readable format in this article.