Coronal mass ejections (CMEs) are intense solar explosive eruptions and have significant impact on geomagnetic activities. It is important to understand how CMEs evolve as they propagate in the solar-terrestrial space. In this paper, we studied the coalescence of magnetic flux ropes embedded in five interplanetary coronal mass ejections (ICMEs) observed by both ACE and Wind spacecraft. The analyses show that coalescence of magnetic flux ropes could persist for hours and operate in scale of hundreds of earth radii. The two merging flux ropes could be very different in the axial orientation and the plasma density and temperature, which should complicate the progress of coalescence and have impact on the merged structures. The study indicates that coalescence of magnetic flux ropes should be an important factor in changing the magnetic topology of ICMEs.

The angular width of a coronal mass ejection (CME) is an important factor in determining whether the corresponding interplanetary CME (ICME) and its preceding shock will reach Earth. However, there have been very few studies of the decisive factors of the CME’s angular width. In this study, we use the three-dimensional (3D) angular width of CMEs obtained from the Graduated Cylindrical Shell model based on observations of Solar Terrestrial Relations Observatory (STEREO) to study the relations between the CME’s 3D width and characteristics of the CME’s source region. We find that for the CMEs produced by active regions (ARs), the CME width has some correlations with the AR’s area and flux, but these correlations are not strong. The magnetic flux contained in the CME seems to come from only part of the AR’s total flux. For the CMEs produced by flare regions, the correlations between the CME angular width and the flare region’s area and flux are strong. The magnetic flux within those CMEs seems to come from the whole flare region or even from a larger region than the flare. Our findings show that the CME’s 3D angular width can be generally estimated based on observations of Solar Dynamics Observatory for the CME’s source region instead of the observations from coronagraphs on board the Solar and Heliospheric Observatory andSTEREO if the two foot points of the CME stay in the same places with no expansion of the CME in the transverse direction until reaching Earth.

Small interplanetary magnetic flux ropes (SIMFRs) are often detected by space satellites in the interplanetary space near 1 AU. These ropes can be fitted by a cylindrically symmetric magnetic model. The durations of SIMFRsare usually <12 h, and the diameters of SIMFRsare <0.20 AU and show power law distribution. Most SIMFRs are observed in the typically slow solar wind (<500 km/s), and only several events are observed with high speed (>700 km/s). Some SIMFRs demonstrate abnormal heavy ion compositions, such as abnormally high He abundance, abnormally high average iron ionization, and enhanced O

During solar eruptions, many closed magnetic flux ropes are ejected into interplanetary space, which contribute to the heliospheric magnetic field and have important space weather effect because of their coherent magnetic field. Therefore, understanding the evolution of these closed flux ropes in the interplanetary space is important. In this paper, we examined all the magnetic and plasma data measured in 1997 by the Wind spacecraft and identified 621 reconnection exhausts. Of the 621 reconnection events, 31 were observed at the boundaries of magnetic flux ropes and were thought to cause the opening or disconnection magnetic field lines of the adjacent ropes. Of the 31 magnetic reconnection events, 29 were interchange reconnections and the closed field lines of these related flux ropes were opened by them. Only 2 of the 31 magnetic reconnection events disconnected the opened field lines of the original flux ropes. These observations indicate that interchange reconnection and disconnection may be two important mechanisms changing the magnetic topology of the magnetic flux ropes during their propagation during the interplanetary space.

Within the known universe, more than 99% of all observable matter is plasma, a state often highly dynamic and far from thermal, as well as mechanical, equilibrium. In particular, for our own solar-terrestrial system, various plasma active phenomena frequently occur such as solar flares, coronal plasma heating, solar wind acceleration, and coronal mass ejections in the solar atmosphere; interplanetary magnetic clouds and collisionless shock waves in interplanetary space; and geomagnetic storms and substorms (also called Earth's aurora) in Earth's magnetosphere and ionosphere. Such phenomena are not only the most important events that are changing the space environment around our anthrosphere, but also provide natural laboratories for us to study in detail basic plasma processes encountered in astrophysics.Since the space age began, enormous effort has been dedicated to in situ explorations and remote sensing observations of plasma active phenomena associated with our solar-terrestrial system. With technical improvements in observational equipment and measuring instruments on board satellites, the analysis of experimental data of these active phenomena and the relevant numerical simulations have attracted much attention from many researchers enabling remarkable progress than ever before. Meanwhile, we are having to face more and more theoretical challenges in understanding basic plasma physics processes underlying all such phenomena, such as (1) microphysical mechanisms for energy conversion in magnetic reconnections; (2) acceleration, propagation, and transport processes of energetic particle beams in collisionless magnetized plasmas; (3) microphysical mechanisms for the formation and dissipation of collisionless shock waves and other discontinuities; (4) emission mechanisms for solar radio bursts and relevant magneto-plasma diagnostic messages; (5) formation and maintenance mechanisms for various fine magneto-plasma structures (i.e. solar coronal loops, discrete auroral arcs, zonal flows, vortices, filaments); and (6) microphysical pictures of energization and thermalization of plasma particles, as well as their associated linear and nonlinear instabilities, resonant and non-resonant wave-particle interactions, and dissipative and non-dissipative turbulent wave dynamics.Contemporary scientific studies rest on three foundation stones: theory, observation, and simulation. Of these, theory attracts the least attention. During the week of June 20-24, 2011, about 40 participants from the fields of solar physics, space physics and plasma physics met at Luoyang Normal College, Luoyang, China, to discuss some key and basic plasma physics processes in solar-terrestrial active phenomena at a mini-workshop on "Basic Plasma Processes in Solar-Terrestrial Activities", organized by Purple Mountain Observatory of Chinese Academy of Sciences, China. One of the motivating considerations for holding this workshop was to offer an opportunity for exchanges among members from different research communities working in solar physics, ...