scholarly journals Solar activities observed with the New Vacuum Solar Telescope

2015 ◽  
Vol 11 (S320) ◽  
pp. 315-320
Author(s):  
Shuhong Yang ◽  
Jun Zhang
Keyword(s):  
Magnetic Reconnection ◽  
Flux Rope ◽  
Observational Evidence ◽  
Small Scale ◽  
Solar Telescope ◽  
New Name ◽  
Direct Observations ◽  
Filament Activation ◽  
First Time

AbstractBased on the New Vacuum Solar Telescope observations, some new results about the solar activities are obtained. (1) In the Hα line, a flux rope tracked by filament activation is detected for the first time. There may exist some mild heating during the filament activation. (2) The direct observations illustrate the mechanism of confined flares, i.e., the flares are triggered by magnetic reconnection between the emerging loops and the pre-existing loops and prevented from being eruptive by the overlying loops. (3) The solid observational evidence of magnetic reconnection between two sets of small-scale loops is reported. The successive slow reconnection changes the conditions around the reconnection area and leads to the rapid reconnection. (4) An ensemble of oscillating bright features rooted in a light bridge is observed and given a new name, light wall. The light wall oscillations may be due to the leakage of p-modes from below the photosphere.

scholarly journals Why are CMEs large-scale coronal events: nature or nurture?

2008 ◽  
Vol 26 (10) ◽  
pp. 3077-3088 ◽  
Author(s):  
L. van Driel-Gesztelyi ◽  
G. D. R. Attrill ◽  
P. Démoulin ◽  
C. H. Mandrini ◽  
L. K. Harra
Keyword(s):  
Magnetic Reconnection ◽  
Large Scale ◽  
Observational Evidence ◽  
Angular Width ◽  
Small Scale ◽  
Apparent Contradiction ◽  
Lower Corona ◽  
Magnetic Structures ◽  
Source Regions ◽  
Scale Response

Abstract. The apparent contradiction between small-scale source regions of, and large-scale coronal response to, coronal mass ejections (CMEs) has been a long-standing puzzle. For some, CMEs are considered to be inherently large-scale events – eruptions in which a number of flux systems participate in an unspecified manner, while others consider magnetic reconnection in special global topologies to be responsible for the large-scale response of the lower corona to CME events. Some of these ideas may indeed be correct in specific cases. However, what is the key element which makes CMEs large-scale? Observations show that the extent of the coronal disturbance matches the angular width of the CME – an important clue, which does not feature strongly in any of the above suggestions. We review observational evidence for the large-scale nature of CME source regions and find them lacking. Then we compare different ideas regarding how CMEs evolve to become large-scale. The large-scale magnetic topology plays an important role in this process. There is amounting evidence, however, that the key process is magnetic reconnection between the CME and other magnetic structures. We outline a CME evolution model, which is able to account for all the key observational signatures of large-scale CMEs and presents a clear picture how large portions of the Sun become constituents of the CME. In this model reconnection is driven by the expansion of the CME core resulting from an over-pressure relative to the pressure in the CME's surroundings. This implies that the extent of the lower coronal signatures match the final angular width of the CME.

scholarly journals NEW VACUUM SOLAR TELESCOPE OBSERVATIONS OF A FLUX ROPE TRACKED BY A FILAMENT ACTIVATION

2014 ◽  
Vol 784 (2) ◽  
pp. L36 ◽  
Author(s):  
Shuhong Yang ◽  
Jun Zhang ◽  
Zhong Liu ◽  
Yongyuan Xiang
Keyword(s):  
Flux Rope ◽  
Solar Telescope ◽  
Filament Activation

Flux Rope Acceleration and Enhanced Magnetic Reconnection Rate

2003 ◽  
Author(s):  
C.Z. Cheng ◽  
Y. Ren ◽  
G.S. Choe ◽  
Y.-J. Moon
Keyword(s):  
Magnetic Reconnection ◽  
Flux Rope ◽  
Reconnection Rate

scholarly journals The Location of Magnetic Reconnection at Earth’s Magnetopause

2021 ◽  
Vol 217 (3) ◽  
Author(s):  
K. J. Trattner ◽  
S. M. Petrinec ◽  
S. A. Fuselier
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Ion Beams ◽  
Review Article ◽  
Observational Evidence ◽  
Magnetic Shear ◽  
General Direction ◽  
Shear Model ◽  
Wide Range

AbstractOne of the major questions about magnetic reconnection is how specific solar wind and interplanetary magnetic field conditions influence where reconnection occurs at the Earth’s magnetopause. There are two reconnection scenarios discussed in the literature: a) anti-parallel reconnection and b) component reconnection. Early spacecraft observations were limited to the detection of accelerated ion beams in the magnetopause boundary layer to determine the general direction of the reconnection X-line location with respect to the spacecraft. An improved view of the reconnection location at the magnetopause evolved from ionospheric emissions observed by polar-orbiting imagers. These observations and the observations of accelerated ion beams revealed that both scenarios occur at the magnetopause. Improved methodology using the time-of-flight effect of precipitating ions in the cusp regions and the cutoff velocity of the precipitating and mirroring ion populations was used to pinpoint magnetopause reconnection locations for a wide range of solar wind conditions. The results from these methodologies have been used to construct an empirical reconnection X-line model known as the Maximum Magnetic Shear model. Since this model’s inception, several tests have confirmed its validity and have resulted in modifications to the model for certain solar wind conditions. This review article summarizes the observational evidence for the location of magnetic reconnection at the Earth’s magnetopause, emphasizing the properties and efficacy of the Maximum Magnetic Shear Model.

scholarly journals On the Relationship between Low Latitude Scintillation Onset and Sunset Terminator over Africa

2021 ◽  
Vol 13 (11) ◽  
pp. 2087
Author(s):  
Mogese Wassaie Mersha ◽  
Elias Lewi ◽  
Norbert Jakowski ◽  
Volker Wilken ◽  
Jens Berdermann ◽  
...  
Keyword(s):  
Moving Boundary ◽  
Occurrence Rate ◽  
Scintillation Index ◽  
Small Scale ◽  
Bahir Dar ◽  
Remarkable Change ◽  
Equatorial Africa ◽  
Night Side ◽  
Solar Terminator ◽  
First Time

The solar terminator is a moving boundary between day-side and night-side regions on the Earth, which is a substantial source of perturbations in the ionosphere. In the vicinity of the solar terminator, essential parameters like S4 index measurements are widely analyzed in order to monitor and predict perturbations in the ionosphere. The utilization of the scintillation index S4 is a well-accepted approach to describe the amplitude/intensity fluctuation of a received signal, predominantly caused by small-scale irregularities of the ionospheric plasma. We report on the longitudinal daily and seasonal occurrence of GNSS signal scintillations, using the data derived from the GNSS stations in Bahir Dar, Ethiopia, Lomé, Togo and Dakar, Senegal. The observed seasonal climatology of GNSS signal scintillations in equatorial Africa is adequately explained by the alignment of the solar terminator and local geomagnetic declination line. It should be pointed out that the strongest scintillations are most frequently observed during the time when the solar terminator is best aligned with the geomagnetic declination line. At all three stations, the comparison of computational and observational results indicated that the scintillation activity culminated around equinoxes in the years 2014, 2015 and 2016. Comparatively, the western equatorial Africa sector has the most intense, longest-lasting, and highest scintillation occurrence rate in equinoctial seasons in all three years. For the first time, we show that the seasonal variation of the scintillation peaks changes systematically from west to east at equatorial GNSS stations over Africa. A detailed analysis of the solar day–night terminator azimuth at ionospheric heights including the time equation shows that the scintillation intensity has a maximum if the azimuth of the terminator coincides with the declination line of the geomagnetic field. Due to the remarkable change of the declination by about 10° at the considered GNSS stations, the distance between scintillation peaks increases by 46 days when moving westward from the Bahir Dar to the Dakar GNSS station. The observations agree quite well with the computational results, thus confirming Tsunoda’s theory.

Corrosion Testing of Armour Wire in Simulated Annulus Environments of Flexible Pipelines: An Update

2003 ◽  
Author(s):  
Richard Clements ◽  
Andrew D. Ethridge
Keyword(s):  
Deionized Water ◽  
Small Scale ◽  
General Corrosion ◽  
Flexible Pipe ◽  
Scale Test ◽  
Condensed Water ◽  
Test Cells ◽  
Sour Service ◽  
First Time ◽  
Permeation Models

This paper describes further investigations, utilising small scale test cells, into the general corrosion which can occur on wires within the inherent annulus space in a flexible pipe, particularly, and for the first time, in a sour service (H2S containing) environment. The work enhances data presented previously in 2002. Tests have been performed in cells specifically designed to simulate, as closely as possible, the environment and confines of a flexible pipe annulus, using solutions of both deionized water and seawater (to represent seawater flooding and condensed water). The systems were saturated with CO2 and H2S to simulate permeation of gases through the polymer pressure sheath (as predicted by validated permeation models). Weight loss measurements were undertaken in order to quantify the corrosion rate in these simulated annulus environments and metallography was undertaken to characterise the corrosion and check for HIC/SOHIC.

scholarly journals “Audience exchange”: cultivating peer-to-peer dialogue at unfamiliar arts events

2017 ◽  
Vol 7 (1) ◽  
pp. 65-79 ◽  
Author(s):  
Stephanie Pitts ◽  
Jonathan Gross
Keyword(s):  
Peer Learning ◽  
Peer To Peer ◽  
Small Scale ◽  
Exchange Method ◽  
Audience Engagement ◽  
Content Type ◽  
Peer Dialogue ◽  
Targeted Marketing ◽  
Audience Development ◽  
First Time

Purpose The purpose of this paper is to demonstrate the usefulness of the “audience exchange” approach for audience development and research, and to highlight the insights offered by peer-to-peer dialogue in understanding experiences of unfamiliar arts. Design/methodology/approach Using a case study with contemporary arts audiences, and setting this in the wider context of studies with other first-time attenders at a range of arts events, the paper explores the use of the “audience exchange” method, in which facilitated conversations after performance events allow newcomers to reflect upon and deepen their first-time encounters with live arts. Findings The study demonstrates the way in which conversations about arts events can enrich audience experience, and shows how participants use exploratory and emotional language to articulate their understanding of unfamiliar arts events. Peer-to-peer learning occurs through these conversations, in ways that could be further supported by arts organisations as a valuable tool for audience development. The audience exchange discussions also reveal the varieties of participation from “drifting” to full attention that are all part of audience engagement. Research limitations/implications This is a small-scale, qualitative study, and the method has potential to be tested in future studies with a greater variety of participants (e.g. younger or more ethnically diverse groups). Practical implications Use of the audience exchange for enriching experiences of first-time attendance could be adopted by arts organisations as a regular part of their audience engagement. Greater understanding of how new audience members draw on prior cultural experiences in finding the language to articulate their first impressions of an unfamiliar arts event could be valuable for targeted marketing and increasing accessibility. Originality/value The originality of this study lies in its elaboration of the audience exchange method, and its focus on the language and peer-to-peer learning evident in the facilitated post-performance discussions.

scholarly journals Ion Dynamics in the Meso-scale 3-D Kelvin–Helmholtz Instability: Perspectives From Test Particle Simulations

2021 ◽  
Vol 8 ◽  
Author(s):  
Xuanye Ma ◽  
Peter Delamere ◽  
Katariina Nykyri ◽  
Brandon Burkholder ◽  
Stefan Eriksson ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Test Particle ◽  
Acoustic Waves ◽  
Particle Simulation ◽  
Three Dimensions ◽  
Small Scale ◽  
Physical Processes ◽  
Length Scales ◽  
Ion Species

Over three decades of in-situ observations illustrate that the Kelvin–Helmholtz (KH) instability driven by the sheared flow between the magnetosheath and magnetospheric plasma often occurs on the magnetopause of Earth and other planets under various interplanetary magnetic field (IMF) conditions. It has been well demonstrated that the KH instability plays an important role for energy, momentum, and mass transport during the solar-wind-magnetosphere coupling process. Particularly, the KH instability is an important mechanism to trigger secondary small scale (i.e., often kinetic-scale) physical processes, such as magnetic reconnection, kinetic Alfvén waves, ion-acoustic waves, and turbulence, providing the bridge for the coupling of cross scale physical processes. From the simulation perspective, to fully investigate the role of the KH instability on the cross-scale process requires a numerical modeling that can describe the physical scales from a few Earth radii to a few ion (even electron) inertial lengths in three dimensions, which is often computationally expensive. Thus, different simulation methods are required to explore physical processes on different length scales, and cross validate the physical processes which occur on the overlapping length scales. Test particle simulation provides such a bridge to connect the MHD scale to the kinetic scale. This study applies different test particle approaches and cross validates the different results against one another to investigate the behavior of different ion species (i.e., H+ and O+), which include particle distributions, mixing and heating. It shows that the ion transport rate is about 1025 particles/s, and mixing diffusion coefficient is about 1010 m2 s−1 regardless of the ion species. Magnetic field lines change their topology via the magnetic reconnection process driven by the three-dimensional KH instability, connecting two flux tubes with different temperature, which eventually causes anisotropic temperature in the newly reconnected flux.

scholarly journals Transient brightenings in the quiet Sun detected by ALMA at 3 mm

2020 ◽  
Vol 638 ◽  
pp. A62 ◽  
Author(s):  
A. Nindos ◽  
C. E. Alissandrakis ◽  
S. Patsourakos ◽  
T. S. Bastian
Keyword(s):  
Solar Atmosphere ◽  
Power Law ◽  
Small Scale ◽  
Solar Chromosphere ◽  
Average Intensity ◽  
Quiet Sun ◽  
Brightness Temperatures ◽  
Weak Preference ◽  
Thermal Origin ◽  
First Time

Aims. We investigate transient brightenings, that is, weak, small-scale episodes of energy release, in the quiet solar chromosphere; these episodes can provide insights into the heating mechanism of the outer layers of the solar atmosphere. Methods. Using Atacama Large Millimeter/submillimeter Array (ALMA) observations, we performed the first systematic survey for quiet Sun transient brightenings at 3 mm. Our dataset included images of six 87″ × 87″ fields of view of the quiet Sun obtained with angular resolution of a few arcsec at a cadence of 2 s. The transient brightenings were detected as weak enhancements above the average intensity after we removed the effect of the p-mode oscillations. A similar analysis, over the same fields of view, was performed for simultaneous 304 and 1600 Å data obtained with the Atmospheric Imaging Assembly. Results. We detected 184 3 mm transient brightening events with brightness temperatures from 70 K to more than 500 K above backgrounds of ∼7200 − 7450 K. All events showed light curves with a gradual rise and fall, strongly suggesting a thermal origin. Their mean duration and maximum area were 51.1 s and 12.3 Mm2, respectively, with a weak preference of appearing at network boundaries rather than in cell interiors. Both parameters exhibited power-law behavior with indices of 2.35 and 2.71, respectively. Only a small fraction of ALMA events had either 304 or 1600 Å counterparts but the properties of these events were not significantly different from those of the general population except that they lacked their low-end energy values. The total thermal energies of the ALMA transient brightenings were between 1.5 × 1024 and 9.9 × 1025 erg and their frequency distribution versus energy was a power law with an index of 1.67 ± 0.05. We found that the power per unit area provided by the ALMA events could account for only 1% of the chromospheric radiative losses (10% of the coronal ones). Conclusions. We were able to detect, for the first time, a significant number of weak 3 mm quiet Sun transient brightenings. However, their energy budget falls short of meeting the requirements for the heating of the upper layers of the solar atmosphere and this conclusion does not change even if we use the least restrictive criteria possible for the detection of transient brightenings.

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