Comparative Analyses of Plasma Properties and Composition in Two Types of Small-scale Interplanetary Flux-ropes

The origin of small-scale interplanetary magnetic flux-ropes (SIMFRs) and the relationship between SIMFRs and magnetic clouds (MCs) are still controversial. In this study, two populations of SMIFRs were collected, i.e., SIMFRs originating from the Sun (SIMFR-SUN) and those originating from the solar wind (SIMFR-SW). We defined the SIMFR-SUN (SIMFR-SW) as the SMIFRs that include (exclude) the counter-streaming suprathermal electrons and stay away from (close to) the heliospheric current sheet. After fitting with force-free flux-rope model, 52 SIMFR-SUN and 57 SIMFR-SW events observed by Advanced Composition Explorer from 1998 February to 2011 August were qualified. Using the approach of relating the measurements to their spatial position within the flux ropes, a comparative survey of plasma and composition characteristics inside the two populations of SIMFRs is presented. Results show that the two populations of SIMFRs have apparent differences. Compared with SIMFR-SW, SIMFR-SUN are MC-like, featuring lower central proton density, higher Vrad, higher low-FIP element abundances, higher and more fluctuate average ion charge-states and the ion charge-state ratios that are related to the heating in the low corona. In addition, for the ion charge-state distributions inside SIMFR-SUN, the sunward side is higher than earthward, which might be caused by the flare heating during eruption. Moreover, both SIMFR-SUN and MCs show anticorrelation between plasma β and the He/P trend. These characteristics indicate that SIMFR-SUN and MCs are very likely to have identical origination. This study supports the two-source origin of SIMFRs, i.e., the solar corona and the solar wind.