A statistical analysis of properties of small transients in the solar wind 2007–2009: STEREO and Wind observations

Abstract

We present a comprehensive statistical analysis of small solar wind transients (STs) in [2007][2008][2009]. Extending work on STs by Kilpua et al. (2009) to a 3 year period, we arrive at the following identification criteria: (i) a duration < 12 h, (ii) a low proton temperature and/or a low proton beta, and (iii) enhanced field strength relative to the 3 year average. In addition, it must have at least one of the following: (a) decreased magnetic field variability, (b) large, coherent rotation of the field vector, (c) low Alfvén Mach number, and (d) T e ∕T p higher than the 3 year average. These criteria include magnetic flux ropes. We searched for STs using Wind and STEREO data. We exclude Alfvénic fluctuations. Case studies illustrate features of these configurations. In total, we find 126 examples, ∼ 81% of which lie in the slow solar wind (≤ 450 km s −1 ). Many start or end with sharp field and flow gradients/discontinuities. Year 2009 had the largest number of STs. The average ST duration is ∼ 4.3 h, 75% < 6 h. Comparing with interplanetary coronal mass ejections (ICMEs) in the same solar minimum, we find the major difference to be that T p in STs is not significantly less than the expected T p . Thus, whereas a low T p is generally considered a very reliable signature of ICMEs, it is not a robust signature of STs. Finally, since plasma ∼ 1, force-free modeling of STs having a magnetic flux rope geometry may be inappropriate.

Formation and Reconnection of Three-dimensional Current Sheets with a Guide Field in the Solar Corona

“…Higginson et al (2017c) have demonstrated that the 3D structure of reconnection-generated magnetic islands in the heliospheric current sheet are consistent with the observations of small-scale flux rope transients in the slow solar wind (Feng et al 2008;Cartwright & Moldwin 2008Kilpua et al 2009;Yu et al 2014). And Janvier et al (2014) have argued that the power-law distribution of the sizes of these small flux rope transients appears compatible with the power-law distributions of magnetic island plasmoids obtained in various reconnection studies (e.g.…”

Small solar wind transients at 1 AU: STEREO observations (2007–2014) and comparison with near‐Earth wind results (1995–2014)

“…To derive the electron contribution to the plasma pressure, we use the result of Newbury et al [], who gave an estimate for T e based on data from the ISEE spacecraft. They obtained T e =1.42 × 10 5 K. Yu et al [, Figure 21] studied Wind data for the 3 years 2007–2009 and obtained for T e the average value of 1.51 × 10 5 K, which is close to Newbury et al 's [] result. Therefore, when examining STEREO data, we use T e =1.42 × 10 5 K, and let N e = N p when we calculate the β plasma .…”

“…For it to be classified as Alfvénic, we require all three correlations to be greater than 0.5 or two greater than 0.6 and the other greater than 0.3, which is similar to the criterion in Cartwright and Moldwin []. Examples were given in Yu et al [, Figures 5 and 6].…”

Counterstreaming electrons in small interplanetary magnetic flux ropes

“…Therefore, Feng et al [] proposed that SIMFRs originate from the Sun and are interplanetary manifestations of small coronal mass ejections (CMEs). In addition, some authors discussed the origin of SIMFRs by investigating the possible relationship between SIMFRs and MCs and found that SIMFRs and MCs have many common and similar (or relative) characteristics [e.g., Feng et al , , , ; Cartwright and Moldwin, ; Feng and Wu, ; Yu et al , ; Janvier et al , , ; Feng and Wang, ]. These authors tend to agree with the view that SIMFRs originate from solar corona.…”