Magnetic reconnection as a possible heating mechanism of the local high temperature protons within magnetic clouds

Magnetic clouds have the outstanding observational features of low proton temperature and plasma beta value, but numerous observations show that some magnetic clouds often have local high temperature phenomena. The local high temperature protons may be heated by magnetic reconnections within magnetic clouds. Here we take the magnetic cloud on 18–20 October 1995 as an example to discuss the possible heating mechanism. There is a famous protuberance in proton temperature between the front boundary and 11: 00 UT on 19 October 1995. Eight magnetic reconnection events were identified within the magnetic cloud, whose duration was less than 31 hours, and most of these reconnection events occurred within the proton temperature enhanced part of the magnetic cloud. Hence, it is possible for the local protons in the magnetic cloud to be heated by magnetic reconnections.

Observational connection between local high-temperature phenomena within magnetic clouds and the Sun

Magnetic clouds(MCs) frequently show abnormal high-ionization states of heavy ions. The abnormal high-charge distributions are related to the coronal temperature of their source regions. We examined the plasma and magnetic field data of 74 MCs observed by the Advanced Composition Explorer from February 1998 to December 2008. We determined that 14 of the 74 events showed local high-temperature phenomena. We analyzed the correlation between proton temperature and O7/O6ratio(or high mean Fe charge state ?Fe?) within the local high-temperature regions in the 14 MCs. Results show that proton temperature and O7/O6 ratio(or high mean Fe charge state) had good correlations in nine MCs, but had no evident correlation in the other five MCs. The local high-temperature phenomena within the nine MCs have resulted from the Sun.

Local high-temperature phenomena within magnetic clouds

In this study,three methods were used to analyze 17 large-scale local high-temperature regions with durations exceeding 2 h within magnetic clouds(MCs)observed by advanced composition explorer from 1998 to 2008.Results show that five of these large-scale regions may have been caused by flare heating;seven of the regions may have been caused by nonuniform expansion when MCs propagated in the solar-terrestrial space;four large-scale high temperature regions may likely result from combined non-uniform expansion and flare heating;and only one large-scale local high-temperature region was not related to either flare heating nor non-uniform expansion.No evidence indicated that magnetic reconnection occurred or had occurred within the high-temperature regions.Based on our results,we infer that such local high-temperature phenomena within MCs are caused primarily as a result of flare heating and non-uniform expansion,either separately or jointly,and that magnetic reconnection plays only a minor role in the formation of high-temperature regions.

Evolution of filamentary molecular clouds in the presence of magnetic fields

The purpose of this paper is to explore the effect of magnetic fields on the dynamics of magnetized filamentary molecular clouds. We suppose there is a filament with cylindrical symmetry and two components of axial and toroidal magnetic fields. In comparison to previous works, the novelty in the present work involves a similarity solution that does not define a function of the magnetic fields or density. We consider the effect of the magnetic field on the collapse of the filament in both axial and toroidal directions and show that the magnetic field has a braking effect, which means that the increasing intensity of the magnetic field reduces the velocity of collapse. This is consistent with other studies. We find that the magnetic field in the central region tends to be aligned with the filament axis. Also, the magnitude and the direction of the magnetic field depend on the magnitude and direction of the initial magnetic field in the outer region. Moreover, we show that more energy dissipation from the filament causes a rise in the infall velocity.

Alfvénic Fluctuations in an Interplanetary Coronal Mass Ejection Observed Near 1 AU

As for the present situation of coronal mass ejection （CME） triggering models, the distributions of Alfv@n waves in flux ropes are different from model to model, and thus examining those distributions in interplanetary coronal mass ejection （ICME） is an effective way to connect ICME observations with these theoretical models of CME triggering. However, previous observations of Alfv@nic fluctuations in ICMEs were rare with locations ranging from 0.3 AU to 0.68 AU only, which is usually explained as rapid dissipation of those remnant waves. Here we present an observation of Alfv@n waves in a magnetic cloud （MC） near 1 AU, in situ detected by WIND in February 17,-~20, 2011. The MC was generated by a CME accompanied with the first X-class flare in the 24th solar cycle. The slope of the power spectral densities of magnetic fluctuation in the MC, are similar to those modes in ambient solar wind, but more anisotropic. The results will also be helpful for studies of CME theories and ICME thermodynamics.

The Grad-Shafranov reconstruction in twenty years: 1996–2016

We review and summarize the applications of the Grad-Shafranov(GS) reconstruction technique to space plasma structures in the Earth's magnetosphere and in the interplanetary space. We organize our presentations following the branches of the "academic family tree" rooted on Prof. Bengt U. ? Sonnerup, the inventor of the GS method. Special attentions are paid to validations of the GS reconstruction results via(1) the direct validation by co-spatial in-situ measurements among multiple spacecraft, and(2) indirect validation by implications and interpretations of the physical connection between the structures reconstructed and other related processes. For the latter, the inter-comparison and interconnection between the large-scale magnetic flux ropes(i.e., Magnetic Clouds) in the solar wind and their solar source properties are presented. In addition, we also summarize various GS-type(or-like) reconstruction and an extension of the GS technique to toroidal geometry. In particular,we point to a possible advancement with added complexity of "helical symmetry" and mixed helicity, in the hope of stimulating interest in future development. We close by offering some thoughts on appreciating the scientific merit of GS reconstruction in general.

Characteristics and applications of interplanetary coronal mass ejection composition

In situ measurements of interplanetary coronal mass ejection(ICME)composition,including elemental abundances and charge states of heavy ions,open a new avenue to study coronal mass ejections(CMEs)besides remote-sensing observations.The ratios between different elemental abundances can diagnose the plasma origin of CMEs(e.g.,from the corona or chromosphere/photosphere)due to the first ionization potential(FIP)effect,which means elements with different FIPs get fractionated between the photosphere and corona.The ratios between different charge states of a specific element can provide the electron temperature of CMEs in the corona due to the freeze-in effect,which can be used to investigate their eruption process.In this review,we first give an overview of the ICME composition and then demonstrate their applications in investigating some important subjects related to CMEs,such as the origin of filament plasma and the eruption process of magnetic flux ropes.Finally,we point out several important questions that should be addressed further for better utilizing the ICME composition to study CMEs.