We investigate the interaction between two filaments and the subsequent filament eruption event observed from different viewing angles by Hinode, the Solar and Heliospheric Observatory, and the Solar Terrestrial Relations Observatory. In the event, the two filaments rose high, interacted with each other, and finally were ejected along two different paths. We measure the bulk-flow velocity using spectroscopic data. We find significant outflows at the speed of a few hundreds of km s 1 during the filament eruption, and also some downflows at a few tens of km s 1 at the edge of the eruption region in the late stage of the eruption. The erupting material was composed of plasmas with a wide temperature range of 10 4 -10 6 K. These results shed light on the filament nature and the coronal dynamics.
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
In solar radiophysics,many theories for type Ⅲ bursts have been proposed during the past 60 years.Almost all these theories are based on the plasma hypothesis,which assumes that(i)the radiation is mainly generated by Langmuir waves via nonlinear processes and(ii)the radiation has frequencies close to the local plasma frequency and/or its second harmonic in the source region. We feel strongly that it is time to advocate an alternative approach without recourse to the plasma hypothesis.This brief discussion explains why.
With the aim of studying the relationship between the relative motions of the loop-top (LT) source and footpoints (FPs) during the rising phase of solar flares, we give a detailed analysis of the X7.1 class flare that occurred on 2005 January 20. The flare was clearly observed by RHESSI, showing a distinct X-ray flaring loop with a bright LT source and two well-defined hard X-ray (HXR) FPs. In particular, we correct the projection effect for the positions of the FPs and magnetic polarity inversion line. We find that: (1) The LT source showed an obvious U-shaped trajectory. The source of the higher energy LT shows a faster downward/upward speed. (2) The evolution of FPs was temporally correlated with that of the LT source. The converging/separating motion of FPs corresponds to the downward/upward motion of the LT source. (3) The initial flare shear of this event is found to be nearly 50 degrees, and it has a fluctuating decrease throughout the contraction phase as well as the expansion phase. (4) Four peaks of the time profile of the unshearing rate are found to be temporally correlated with peaks in the HXR emission flux. This flare supports the overall contraction picture of flares: a descending motion of the LT source, in addition to converging and unshearing motion of FPs. All results indicate that the magnetic field was very highly sheared before the onset of the flare.
Tuan-Hui ZhouJun-Feng WangDong LiQi-Wu SongVictor MelnikovHai-Sheng Ji
Dispersive magnetohydrodynamic (MHD) waves with short-wavelength modification have an important role in transforming energy from waves into particles.In this paper,based on the two-fluid mode,a dispersion equation,including the short-wavelength effect,and its exact solution are presented.The outcome is responsible for the short-wavelength modification versions of the three ideal MHD modes (i.e.the fast,slow and Alfve'n).The results show that the fast and Alfve'n modes are modified considerably by the shortwavelength effect mainly in the quasi-parallel and quasi-perpendicular propagation directions,respectively,while the slow mode can be affected by the short-wavelength effect in all propagation directions.On the other hand,the dispersive modification occurs primarily in the finite-β regime of 0.001 < β < 1 for the fast mode and in the high-β regime of 0.1 < β < 10 for the slow mode.For the Alfve'n mode,the dispersive modification occurs from the low-β regime of β < 0.001 through the high-β regime of β > 1.
Gamma-ray spectroscopy provides a wealth of information about acceler-ated particles in solar flares, as well as the ambient medium with which these energetic particles interact. The neutron capture line (2.223 MeV), the strongest in the solar gamma-ray spectrum, forms in the deep atmosphere. The energy of these photons can be reduced via Compton scattering. With the fully relativistic GEANT4 toolkit, we have carried out Monte Carlo simulations of the transport of a neutron capture line in solar flares, and applied them to the flare that occurred on 2005 January 20 (X7.1/2B), one of the most powerful gamma-ray flares observed by RHESSI during the 23rd solar cycle. By comparing the fitting results of different models with and without Compton scattering of the neutron capture line, we find that when including the Compton scattering for the neutron capture line, the observed gamma-ray spectrum can be reproduced by a population of accelerated particles with a very hard spectrum (s ≤ 2.3). The Compton effect of a 2.223 MeV line on the spectra is therefore proven to be significant, which influences the time evolution of the neutron capture line flux as well. The study also suggests that the mean vertical depth for neutron capture in hydrogen for this event is about 8 g cm 2 .
