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

摘要

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.