The solar corona is frequently disrupted by coronal mass ejections (CMEs), whose core structure is believed to be a flux rope made of helical magnetic field. This has become a “standard” picture; though, it remains elusive how the flux rope forms and evolves toward eruption. While one-third of the ejecta passing through spacecraft demonstrate a flux-rope structure, the rest have complex magnetic fields. Are they originating from a coherent flux rope, too? Here we investigate the source region of a complex ejecta, focusing on a flare precursor with definitive signatures of magnetic reconnection, i.e., nonthermal electrons, flaring plasma, and bidirectional outflowing blobs. Aided by nonlinear force-free field modeling, we conclude that the reconnection occurs within a system of multiple braided flux ropes with different degrees of coherency. The observation signifies the importance of internal structure and dynamics in understanding CMEs and in predicting their impacts on Earth.

Employing coronagraphic and EUV observations close to the solar surface made by the Solar Terrestrial Relations Observatory (STEREO) mission, we determined the heliocentric distance of coronal mass ejections (CMEs) at the starting time of associated metric type II bursts. We used the wave diameter and leading edge methods and measured the CME heights for a set of 32 metric type II bursts from solar cycle 24. We minimized the projection effects by making the measurements from a view that is roughly orthogonal to the direction of the ejection. We also chose image frames close to the onset times of the type II bursts, so no extrapolation was necessary. We found that the CMEs were located in the heliocentric distance range from 1.20 to 1.93 solar radii (Rs), with mean and median values of 1.43 and 1.38 Rs, respectively. We conclusively find that the shock formation can occur at heights substantially below 1.5 Rs. In a few cases, the CME height at type II onset was close to 2 Rs. In these cases, the starting frequency of the type II bursts was very low, in the range 25 -40 MHz, which confirms that the shock can also form at larger heights. The starting frequencies of metric type II bursts have a weak correlation with the measured CME/shock heights and are consistent with the rapid decline of density with height in the inner corona.

Detrital-zircon fi ssion-track (FT) ages from the Lower Cenozoic Sub-Himalayanforeland basin refl ect the progressive effects of crustal thickening and exhumation on the Himalayan source rocks as a consequence of the India-Asia collision. The oldest stratum, the transgressive marine Paleocene-Eocene Subathu Formation (57-41.5 Ma) contains ca. 50 Ma detrital-zircon P1 peak, which was derived from the Indus Tsangpo Suture Zone and the Ladakh Batholith of the Asian plate. A dominant 302.4 ± 21.9 Ma peak with a few 520 Ma grains in this formation has been derived by erosion of the zircon partialannealing zone (ZPAZ) of 240-180 °C. As the fi rst imprint of the collision, this zone affected the Himalayan Proterozoic basement and its Tethyan sedimentary cover.Since the detritus in the Subathu has been derived both from the Indian and Asian plates, the possible suturing of these plates took place during the Subathu sedimentation. A sudden change in the provenance is recorded in the detrital-zircon FT cooling ages in the OligoMiocene Dagshai and Kasauli Formations, which have dominant 30 and 25 Ma P1 peaks, respectively. We interpret a distinct unconformity spanning ~10 m.y. between the Subathu and Dagshai Formations. Since ca. 30 Ma, molassic sedimentation coincides with shifting of the source rocks to the Himalayan metamorphic belt. This belt has sequentially undergone three distinct cooling and exhumation pulses after the ultrahigh-pressure-high-pressure (UHP-HP) metamorphism (53-50 Ma) in the extreme north and two widespread M1 and M2 metamorphisms (40-30 and 25-15 Ma) in the middle parts. These events appear to be largely responsible for the deposition of the ca. 30 Ma zircon Himalayan peak and ca. 25 and 15 Ma young Himalayan peaks, respectively; the latter appears within the Lower Siwalik Subgroup (13-11 Ma). During the Lower Siwalik deposition, pre-Himalayan peaks gradually decrease with the intensifi cation of the Himalayan events in source rocks. In spite of uninterrupted fl uvial sedimentation in the Dagshai-Kasauli-Lower Siwalik sequences since 30 Ma, breaks of ~5-7 m.y. in the zircon FT ages reveal pulsative cooling and exhumation in the well-identifi ed source areas. Although cooling and exhumation of the Himalayan source rocks remained almost uniform during the Eocene, source heterogeneity is refl ected in fl uvial sedimentation since 37 Ma from Pakistan to Nepal in response to the India-Asia collision.

It is often envisaged that dense filament material lies in the dips of magnetic field lines belonging to either a sheared arcade or a magnetic flux rope. But it is also debated which configuration correctly depicts filaments' magnetic structure, due to our incapacity to measure the coronal magnetic field. In this paper, we address this issue by employing mass motions in an active-region filament to diagnose its magnetic structure. The disturbance in the filament was driven by a surge initiated at the filament's eastern end in the NOAA active region 12685, which was observed by the 1-m New Vacuum Solar Telescope (NVST) in the Hα line center and line wing (±0.4Å). Filament material predominately exhibits two kinds of motions, namely, rotation about the spine and longitudinal oscillation along the spine. The former is evidenced by antisymmetric Doppler shifts about the spine; the latter features a dynamic barb with mass extending away from the Hα spine until the transversal edge of the EUV filament channel. The longitudinal oscillation in the eastern section of the filament is distinct from that in the west, implying that the underlying field lines have different lengths and curvature radii. The composite motions of filament material suggest a double-decker host structure with mixed signs of helicity, comprising a flux rope atop a sheared-arcade system.

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We report solar flare plasma to be multi-thermal in nature based on the theoretical model and study of the energy-dependent timing of thermal emission in ten M-class flares. We employ high-resolution X-ray spectra observed by the Si detector of the "Solar X-ray Spectrometer" (SOXS). The SOXS onboard the Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May 2003. Firstly we model the spectral evolution of the X-ray line and continuum emission flux F() from the flare by integrating a series of isothermal plasma flux.We find that multi-temperature integrated flux F() is a power-law function of  with a spectral index () ≈ -4.65. Next, based on spectral-temporal evolution of the flares we find that the emission in the energy range E= 4 -15 keV is dominated by temperatures of T= 12 -50 MK, while the multi-thermal power-law DEM index () varies in the range of -4.4 and -5.7. The temporal evolution of the X-ray flux F(,t) assuming a multi-temperature plasma governed by thermal conduction cooling reveals that the temperature-dependent cooling time varies between 296 and 4640 s and the electron density (n e ) varies in the range of n e = (1.77-29.3)*10 10 cm -3 . Employing temporal evolution technique in the current study as an alternative method for separating thermal from non-thermal components in the energy spectra, we measure the break-energy point ranging between 14 and 21±1.0 keV.