EUV and coronagraphic observations of coronal mass ejections     

Durgesh Tripathi 《Journal of Astrophysics and Astronomy》2006,27(2-3):193-200

The Large Angle Spectrometric Coronagraph (LASCO) and Extreme-ultraviolet Imaging Telescope (EIT) onboard Solar and Heliospheric Observatory (SOHO) provide us with unprecedented multi-wavelength observations helping us to understand different dynamic phenomena on the Sun and in the corona. In this paper we discuss the association between post-eruptive arcades (PEAs) detected by EIT and white-light coronal mass ejections (CMEs) detected by LASCO/C2 telescope.  相似文献   

Coronal Holes and Icosahedral Symmetry     

Wolfram Neutsch  Herbert Kalisch  Horst Fichtner  S. Ranga Sreenivasan  Maurice Shevalier 《Astrophysics and Space Science》2003,288(3):391-408

The study of the expansion of the solar wind out of a system of coronal holes is continued. To this end, we consider the numerical integration of partial differential equations for problems with icosahedral symmetry, in general. First, employing Weyl theory, orbifold coordinates are introduced. Second, the icosahedral coordinates are discussed in detail. Third, following an analysis of the properties of these coordinates and the derivation of a few expressions useful for grid construction, various alternatives for the distribution of lattice points required for numerical integration are considered. A comparison of these numerical grids motivates the choice of a specific grid optimized for the numerical integration carried out in the accompanying paper by Kalish et al.(2002). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Asymmetrically zoned reaction rims: assessment of grain boundary diffusivities and growth rates related to natural diffusion-controlled mineral reactions   总被引：1，自引：0，他引：1  

L. M. KELLER  R. WIRTH  D. RHEDE  K. KUNZE  R. ABART 《Journal of Metamorphic Geology》2008,26(1):99-120

This study explores garnet coronas around hedenbergite, which were formed by the reaction plagioclase + hedenbergite→garnet + quartz, to derive information about diffusion paths that allowed for material redistribution during reaction progress. Whereas quartz forms disconnected single grains along the garnet/hedenbergite boundaries, garnet forms ～20‐μm‐wide continuous polycrystalline rims along former plagioclase/hedenbergite phase boundaries. Individual garnet crystals are separated by low‐angle grain boundaries, which commonly form a direct link between the reaction interfaces of the plagioclase|garnet|hedenbergite succession. Compositional variations in garnet involve: (i) an overall asymmetric compositional zoning in Ca, Fe²⁺, Fe³⁺ and Al across the garnet layer; and (ii) micron‐scale compositional variations in the near‐grain boundary regions and along plagioclase/garnet phase boundaries. These compositional variations formed during garnet rim growth. Thereby, transfer of the chemical components occurred by a combination of fast‐path diffusion along grain boundaries within the garnet rim, slow diffusion through the interior of the garnet grains, and by fast diffusion along the garnet/plagioclase and the garnet/hedenbergite phase boundaries. Numerical simulation indicates that diffusion of Ca, Al and Fe²⁺ occurred about three to four, four and six to seven orders of magnitude faster along the grain boundaries than through the interior of the garnet grains. Fast‐path diffusion along grain boundaries contributed substantially to the bulk material transfer across the growing garnet rim. Despite the contribution of fast‐path diffusion, bulk diffusion through the garnet rim was too slow to allow for chemical equilibration of the phases involved in garnet rim formation even on a micrometre scale. Based on published garnet volume diffusion data the growth interval of a 20‐μm‐wide garnet rim is estimated at ～10³–10⁴ years at the inferred reaction conditions of 760 ± 50 °C at 7.6 kbar. Using the same parameterization of the growth law, 100‐μm‐ and 1‐mm‐thick garnet rims would grow within 10⁵–10⁶ and 10⁶–10⁷ years respectively.  相似文献   

Scaling-laws of Radio Spike Bursts and Their Constraints on New Solar Radio Telescopestwo     

Tan Bao-lin  Cheng Jun  Tan Cheng-ming  Kou Hong-xiang 《Chinese Astronomy and Astrophysics》2019,43(1):59-74

Radio observation is one of important methods in solar physics and space science. Sometimes, it is almost the sole approach to observe the physical processes such as the acceleration, emission, and propagation of non-thermal energetic particles, etc. So far, more than 100 solar radio telescopes have been built in the world, including solar radiometers, dynamic spectrometers, and radioheliographs. Some of them have been closed after the fulfillment of their primary scientific objectives, or for their malfunctions, and thus replaced by other advanced instruments. At the same time, based on some new technologies and scientific ideas, various kinds of new and much more complicated solar radio telescopes are being constructed by solar radio astronomers and space scientists, such as the American E-OVSA and the solar radio observing system under the framework of Chinese Meridian Project II, etc. When we plan to develop a new solar radio telescope, it is crucial to design the most suitable technical parameters, e.g., the observing frequency range and bandwidth, temporal resolution, frequency resolution, spatial resolution, polarization degree, and dynamic range. Then, how do we select a rational set of these parameters? The long-term observation and study revealed that a large strong solar radio burst is frequently composed of a series of small bursts with different time scales. Among them, the radio spike burst is the smallest one with the shortest lifetime, the narrowest bandwidth, and the smallest source region. Solar radio spikes are considered to be related to a single magnetic energy release process, and can be regarded as an elementary burst in solar flares. It is a basic requirement for the new solar radio telescope to observe and discriminate these solar radio spike bursts, even though the temporal and spatial scales of radio spike bursts actually vary with the observing frequency. This paper presents the scaling laws of the lifetime and bandwidth of solar radio spike bursts with respect to the observing frequency, which provide some constraints for the new solar radio telescopes, and help us to select the rational telescope parameters. Besides, we propose a spectrum-image combination mode as the best observation mode for the next-generation solar radio telescopes with high temporal, spectral, and spatial resolutions, which may have an important significance for revealing the physical essence of the various non-thermal processes in violent solar eruptions.  相似文献   

湖北浠水蓝晶石铝直闪石片岩中的冠状体结构的研究   总被引：11，自引：3，他引：11  

游振东  吕学淼 《地球科学》1990,15(4):345-356

  相似文献   

Decompressional coronas and symplectites in granulites of the Musgrave Complex, central Australia   总被引：2，自引：0，他引：2  

G. L. CLARKE  R. POWELL 《Journal of Metamorphic Geology》1991,9(4):441-450

Abstract In granulite facies metapelitic rocks in the Musgrave Complex, central Australia, reaction between S1 garnet and sillimanite involves the development in S2 of both garnet + cordierite + hercynitic spinel + biotite and hercynitic spinel + cordierite + sillimanite + biotite. The S2 assemblages occur either in coronas and symplectites, mainly around garnet, or, in rocks in which S2 is more strongly developed, as recrystallized assemblages. Ignoring the presence of biotite and ilmenite, the mineral textures can be accounted for qualitatively by a consideration of the model system FeO-MgO-Al₂O₃-SiO₂ (FMAS); the textural relationships accord with decompression accompanying the change from S1 to S2. However, since biotite and ilmenite are involved in the assemblages, the parageneses are better accounted for in terms of equilibria in the expanded model system K₂O-FeO-MgO-Al₂O₃-SiO₂-H₂-TiO₂-Fe₂O₃ (KFMASHTO), i.e. AFM + TiO₂+ Fe₂O₃. The coronas reflect the tectonic unroofing of at least part of the Musgrave Complex from peak S1 conditions of about 8 kbar to S2 conditions of about 4 kbar.  相似文献   

Petrology of spinel granulites from Araku, Eastern Ghats, India, and a petrogenetic grid for sapphirine-free rocks in the system FMAS   总被引：4，自引：0，他引：4  

P. SENGUPTA  S. KARMAKAR  S. DASGUPTA  M. FUKUOKA 《Journal of Metamorphic Geology》1991,9(4):451-459

Abstract Spinel-quartz-cordierite and spinel-quartz are found as relic prograde assemblages in Fe-rich granulites from the Araku area, Eastern Ghats belt, India. Subsequent reactions produced orthopyroxene + sillimanite in the former association and garnet + sillimanite in the latter. The first reaction is univariant in the FMAS system, but is trivariant in the present case because of the presence of Zn and Fe³⁺ in spinel. The second reaction also has high variance because of Zn and Fe³⁺, but also because of the presence of Ca in garnet. Thermobarometry shows that the metamorphic conditions were approximately 950° C and 8.5 kbar and the fo ₂ was near the NNO buffer. In Fe-rich bulk compositions and low- P -high- T conditions of metamorphism, two of the univariant reactions around the invariant point [Sa], namely (Sa, Hy) and (Sa, Cd), change topology due to reverse partitioning of Fe-Mg between coexisting garnet and spinel. An alternative partial petrogenetic grid in the system FMAS is constructed for such conditions and is applied satisfactorily to several sapphirine-free spinel granulites. It is shown that bulk composition ( X _Fe and Zn) exerts greater control on the stability of spinel + quartz than fo ₂. The effect of the presence of Zn and Fe³⁺ in spinel on the proposed grid is evaluated. Reaction textures in the Araku spinel granulites can be explained from the petrogenetic grid as due to near-isobaric cooling.  相似文献   

Plagioclase replacement textures in partially eclogitised gabbros from the Sanddal mafic-ultramafic complex, Greenland Caledonides   总被引：1，自引：0，他引：1  

H. M. Lang  J. A. Gilotti 《Journal of Metamorphic Geology》2001,19(5):497-517

The Sanddal mafic‐ultramafic complex (SMUK) is a cluster of variably eclogitised mafic and ultramafic bodies that comprise the westernmost known eclogite facies locality in the North‐East Greenland eclogite province (NEGEP). Although there are no true eclogites in the SMUK, we interpret three distinct textural types of plagioclase replacement to record sequential stages in adjustment of SMUK olivine gabbro‐norites to eclogite facies conditions. The earliest stage, in which plagioclase was replaced by omphacite/spinel symplectite before nucleation of garnet (Type 1A & 1B) has not previously been described. Documentation of this texture provides clear evidence that, at least in some cases, garnet nucleation is delayed relative to nucleation of omphacite and is a rate‐limiting step for eclogitisation. Type 1C domains were produced by scattered nucleation of garnet in the same sample. In Type 2 domains, plagioclase was replaced by a layered corona with an outer layer of garnet, an inner layer of omphacite and an interior of inclusion‐rich plagioclase. In Type 3 domains, the omphacite layer was overgrown by the garnet rim, and omphacite is preserved only as inclusions in garnet. In more coarse grained leucogabbros, recrystallization was more complete, plagioclase replacement textures were less localised, and could not be divided into distinct stages. Plagioclase replacement in SMUK samples was not isochemical, and required diffusion of at least Mg and Fe from replacement of mafic phases in the surroundings. Strong compositional gradients in garnet reflect disequilibrium and were controlled by the different diffusion rates of Mg/Fe and Ca, different local chemical environments, and progress of the plagioclase breakdown reaction. The presence of small amounts of hydrous minerals (amphibole, phlogopite and clinozoisite) in local equilibrium in plagioclase domains of most SMUK samples indicates that a small amount of H₂O was present during high pressure metamorphism.  相似文献   

The heating of the solar corona     

R.?W.?WalshEmail author  J.?Ireland 《Astronomy and Astrophysics Review》2003,12(1):1-41

The heating of the solar corona has been a fundamental astrophysical issue for over sixty years. Over the last decade in particular, space-based solar observatories (Yohkoh, SOHO and TRACE) have revealed the complex and often subtle magnetic-field and plasma interactions throughout the solar atmosphere in unprecedented detail. It is now established that any energy release mechanism is magnetic in origin - the challenge posed is to determine what specific heat input is dominating in a given coronal feature throughout the solar cycle. This review outlines a range of possible magnetohydrodynamic (MHD) coronal heating theories, including MHD wave dissipation and MHD reconnection as well as the accumulating observational evidence for quasi-periodic oscillations and small-scale energy bursts occurring in the corona. Also, we describe current attempts to interpret plasma temperature, density and velocity diagnostics in the light of specific localised energy release. The progress in these investigations expected from future solar missions (Solar-B, STEREO, SDO and Solar Orbiter) is also assessed.Received: 6 February 2003, Published online: 14 November 2003 Correspondence to: R. W. Walsh  相似文献   

1997年3月9日漠河日全食外日冕结构及相对强度分布     

李秋莎  张柏荣 《天文研究与技术》2000,(2):11

利用简单的视频图像采集系统 ,对 1 997年 3月 9日用PanasonicNV -S880EN型摄像机拍摄的黑龙江漠河日全食黄光 (加GG1 1滤光片 )和白光日冕观测资料进行计算处理 ,得到大于 1 .5R⊙ 的太阳活动低年外日冕结构及其相对强度分布。  相似文献