scholarly journals A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

Solar Physics ◽  
2021 ◽  
Vol 296 (5) ◽  
Author(s):  
Bart De Pontieu ◽  
Vanessa Polito ◽  
Viggo Hansteen ◽  
Paola Testa ◽  
Katharine K. Reeves ◽  
...  
Keyword(s):  
Solar Atmosphere ◽  
Resonant Absorption ◽  
Interface Region ◽  
Machine Learning Techniques ◽  
Small Scale ◽  
Wide Range ◽  
Field Lines ◽  
Far Ultraviolet ◽  
Imaging Spectrograph

AbstractThe Interface Region Imaging Spectrograph (IRIS) has been obtaining near- and far-ultraviolet images and spectra of the solar atmosphere since July 2013. IRIS is the highest resolution observatory to provide seamless coverage of spectra and images from the photosphere into the low corona. The unique combination of near- and far-ultraviolet spectra and images at sub-arcsecond resolution and high cadence allows the tracing of mass and energy through the critical interface between the surface and the corona or solar wind. IRIS has enabled research into the fundamental physical processes thought to play a role in the low solar atmosphere such as ion–neutral interactions, magnetic reconnection, the generation, propagation, and dissipation of waves, the acceleration of non-thermal particles, and various small-scale instabilities. IRIS has provided insights into a wide range of phenomena including the discovery of non-thermal particles in coronal nano-flares, the formation and impact of spicules and other jets, resonant absorption and dissipation of Alfvénic waves, energy release and jet-like dynamics associated with braiding of magnetic-field lines, the role of turbulence and the tearing-mode instability in reconnection, the contribution of waves, turbulence, and non-thermal particles in the energy deposition during flares and smaller-scale events such as UV bursts, and the role of flux ropes and various other mechanisms in triggering and driving CMEs. IRIS observations have also been used to elucidate the physical mechanisms driving the solar irradiance that impacts Earth’s upper atmosphere, and the connections between solar and stellar physics. Advances in numerical modeling, inversion codes, and machine-learning techniques have played a key role. With the advent of exciting new instrumentation both on the ground, e.g. the Daniel K. Inouye Solar Telescope (DKIST) and the Atacama Large Millimeter/submillimeter Array (ALMA), and space-based, e.g. the Parker Solar Probe and the Solar Orbiter, we aim to review new insights based on IRIS observations or related modeling, and highlight some of the outstanding challenges.

scholarly journals The role of Edge-Driven Convection in the generation of volcanism I: a 2D systematic study

2020 ◽  
Author(s):  
Antonio Manjón-Cabeza Córdoba ◽  
Maxim Ballmer
Keyword(s):  
Numerical Models ◽  
High Volume ◽  
Oceanic Lithosphere ◽  
Companion Paper ◽  
Small Scale ◽  
Continental Lithosphere ◽  
Transient Phenomenon ◽  
Mantle Viscosity ◽  
Wide Range

Abstract. The origin of intraplate volcanism is not explained by the plate tectonic theory, and several models have been put forward for explanation. One of these models involves Edge-Driven Convection (EDC), in which cold and thick continental lithosphere is juxtaposed to warm and thin oceanic lithosphere to trigger convective instability. To test whether EDC can produce long-lived high-volume magmatism, we run numerical models of EDC for a wide range of mantle properties and edge (i.e., the oceanic-continental transition) geometries. We find that the most important parameters that govern EDC are the rheological paramaters mantle viscosity η0 and activation energy Ea. However, even the maximum melting volumes found in our models are insufficient to account for island-building volcanism on old seafloor, such as at the Canary Islands and Cape Verde. Also, beneath old seafloor, localized EDC-related melting commonly transitions into widespread melting due to small-scale sublithospheric convection, inconsistent with the distribution of volcanism at these volcanic chains. In turn, EDC is a good candidate to sustain the formation of small seamounts on young seafloor, as it is a highly transient phenomenon that occurs in all our models soon after initiation. In a companion paper, we investigate the implications of interaction of EDC with mantle-plume activity.

scholarly journals The role of edge-driven convection in the generation of volcanism – Part 1: A 2D systematic study

Solid Earth ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 613-632
Author(s):  
Antonio Manjón-Cabeza Córdoba ◽  
Maxim D. Ballmer
Keyword(s):  
Numerical Models ◽  
High Volume ◽  
Oceanic Lithosphere ◽  
Companion Paper ◽  
Rheological Parameters ◽  
Small Scale ◽  
Transient Phenomenon ◽  
Mantle Viscosity ◽  
Wide Range

Abstract. The origin of intraplate volcanism is not explained by plate tectonic theory, and several models have been put forward for explanation. One of these models involves edge-driven convection (EDC), in which cold and thick continental lithosphere is juxtaposed with warm and thin oceanic lithosphere to trigger convective instability. To test whether EDC can produce long-lived high-volume magmatism, we run numerical models of EDC for a wide range of mantle properties and edge (i.e., the oceanic–continental transition) geometries. We find that the most important parameters that govern EDC are the rheological parameters mantle viscosity η0 and activation energy Ea. However, even the maximum melting volumes predicted by our most extreme cases are insufficient to account for island-building volcanism on old seafloor, such as at the Canary Islands and Cabo Verde. Also, beneath old seafloor, localized EDC-related melting commonly transitions into widespread melting due to small-scale sublithospheric convection, inconsistent with the distribution of volcanism at these volcano chains. In turn, EDC is a good candidate to sustain the formation of small seamounts on young seafloor, as it is a highly transient phenomenon that occurs in all our models soon after initiation. In a companion paper, we investigate the implications of interaction of EDC with mantle plume activity (Manjón-Cabeza Córdoba and Ballmer, 2021).

scholarly journals Dynamics of Orographically Triggered Banded Convection in Sheared Moist Orographic Flows

2007 ◽  
Vol 64 (10) ◽  
pp. 3542-3561 ◽  
Author(s):  
Oliver Fuhrer ◽  
Christoph Schär
Keyword(s):  
Small Amplitude ◽  
Three Dimensional ◽  
Horizontal Resolution ◽  
Small Scale ◽  
Mean Flow ◽  
Topographic Roughness ◽  
Wide Range ◽  
Orographic Convection ◽  
Wind Profiles

Abstract Shallow orographic convection embedded in an unstable cap cloud can organize into convective bands. Previous research has highlighted the important role of small-amplitude topographic variations in triggering and organizing banded convection. Here, the underlying dynamical mechanisms are systematically investigated by conducting three-dimensional simulations of moist flows past a two-dimensional mountain ridge using a cloud-resolving numerical model. Most simulations address a sheared environment to account for the observed wind profiles. Results confirm that small-amplitude topographic variations can enhance the development of embedded convection and anchor quasi-stationary convective bands to a fixed location in space. The resulting precipitation patterns exhibit tremendous spatial variability, since regions receiving heavy rainfall can be only kilometers away from regions receiving little or no rain. In addition, the presence of banded convection has important repercussions on the area-mean precipitation amounts. For the experimental setup here, the gravity wave response to small-amplitude topographic variations close to the upstream edge of the cap cloud (which is forced by the larger-scale topography) is found to be the dominant triggering mechanism. Small-scale variations in the underlying topography are found to force the location and spacing of convective bands over a wide range of scales. Further, a self-sufficient mode of unsteady banded convection is investigated that does not dependent on external perturbations and is able to propagate against the mean flow. Finally, the sensitivity of model simulations of banded convection with respect to horizontal computational resolution is investigated. Consistent with predictions from a linear stability analysis, convective bands of increasingly smaller scales are favored as the horizontal resolution is increased. However, small-amplitude topographic roughness is found to trigger banded convection and to control the spacing and location of the resulting bands. Thereby, the robustness of numerical simulations with respect to an increase in horizontal resolution is increased in the presence of topographic variations.

scholarly journals Artistic explorations of Lviv artists of decorative and applied arts in small-scale plastics of the second half of the 20th century: image of a human being

2021 ◽  
Vol IX(258) (47) ◽  
pp. 10-14
Author(s):  
V. Honcharuk
Keyword(s):  
20Th Century ◽  
Art Criticism ◽  
Fine Arts ◽  
Decorative Arts ◽  
Small Scale ◽  
Human Being ◽  
Applied Art ◽  
Wide Range ◽  
Characteristic Features

The present article examines the special characteristics of the development of small-scale sculpture as an independent phenomenon in Lviv fine arts of the second half of the 20th century within the framework of the interpretation of a human being image, since the following problem has not been sufficiently studied in Ukrainian art criticism. In particular, the research focuses on the specific features of artistic experiments of the representatives of decorative and applied art in the field of anthropomorphic sculpture; traces characteristic features of conceptual and modelling solutions; identifies artistic and stylistic features and peculiarities of the representation of a human being image. The author stresses upon the role of Lviv Ceramic and Sculpture Factory that largely set trends in the development of small-scale sculpture. In addition, as based on works of famous representatives of Lviv school of decorative arts, the author identifies the variety of interpretations and wide range of modelling means as well as traces the most vivid anthropomorphic designs.

scholarly journals Lower Crustal Heterogeneity and Fractional Crystallization Control Evolution of Small-volume Magma Batches at Ocean Island Volcanoes (Ascension Island, South Atlantic)

2019 ◽  
Vol 60 (8) ◽  
pp. 1489-1522 ◽  
Author(s):  
K J Chamberlain ◽  
J Barclay ◽  
K J Preece ◽  
R J Brown ◽  
J P Davidson
Keyword(s):  
Fractional Crystallization ◽  
Lower Crust ◽  
South Atlantic ◽  
Small Scale ◽  
Evolutionary Trend ◽  
Diverse Range ◽  
Ocean Island ◽  
Ascension Island ◽  
Wide Range

Abstract Ocean island volcanoes erupt a wide range of magmatic compositions via a diverse range of eruptive styles. Understanding where and how these melts evolve is thus an essential component in the anticipation of future volcanic activity. Here we examine the role of crustal structure and magmatic flux in controlling the location, evolution and ultimately composition of melts at Ascension Island. Located in the South Atlantic, Ascension Island is an ocean island volcano that has produced a continuum of eruptive compositions from basalt to rhyolite in its 1 Myr subaerial eruptive history. Volcanic rocks broadly follow a silica-undersaturated subalkaline evolutionary trend, and new data presented here show a continuous compositional trend from basalt through trachyte to rhyolite. Detailed petrographic observations are combined with in situ geochemical analyses of crystals and glass, and new whole-rock major and trace element data from mafic and felsic pyroclastic and effusive deposits that span the entire range in eruptive ages and compositions found on Ascension Island. These data show that extensive fractional crystallization is the main driver for the production of felsic melts for Ascension Island, a volcano built on thin, young, oceanic crust. Strong spatial variations in the compositions of erupted magmas reveal the role of a heterogeneous lower crust; differing degrees of interaction with a zone of plutonic rocks are responsible for the range in mafic lava compositions, and for the formation of the central and eastern felsic complexes. A central core of nested, small-scale plutonic, or mush-like, bodies inhibits the ascent of mafic magmas, allowing sequential fractional crystallization within the lower crust, and generating felsic magmas in the core of the island. There is no evidence for magma mixing preserved in any of the studied eruptions, suggesting that magma storage regions are transient, and material is not recycled between eruptions.

scholarly journals The role of partial ionization effects in the chromosphere

2015 ◽  
Vol 373 (2042) ◽  
pp. 20140268 ◽  
Author(s):  
Juan Martínez-Sykora ◽  
Bart De Pontieu ◽  
Viggo Hansteen ◽  
Mats Carlsson
Keyword(s):  
Solar Atmosphere ◽  
Energy Transport ◽  
Magnetic Energy ◽  
Interaction Effects ◽  
Ambipolar Diffusion ◽  
Lower Atmosphere ◽  
Induction Equation ◽  
Field Lines ◽  
Magnetohydrodynamic Simulations

The energy for the coronal heating must be provided from the convection zone. However, the amount and the method by which this energy is transferred into the corona depend on the properties of the lower atmosphere and the corona itself. We review: (i) how the energy could be built in the lower solar atmosphere, (ii) how this energy is transferred through the solar atmosphere, and (iii) how the energy is finally dissipated in the chromosphere and/or corona. Any mechanism of energy transport has to deal with the various physical processes in the lower atmosphere. We will focus on a physical process that seems to be highly important in the chromosphere and not deeply studied until recently: the ion–neutral interaction effects in the chromosphere. We review the relevance and the role of the partial ionization in the chromosphere and show that this process actually impacts considerably the outer solar atmosphere. We include analysis of our 2.5D radiative magnetohydrodynamic simulations with the Bifrost code (Gudiksen et al. 2011 Astron. Astrophys. 531 , A154 ( doi:10.1051/0004-6361/201116520 )) including the partial ionization effects on the chromosphere and corona and thermal conduction along magnetic field lines. The photosphere, chromosphere and transition region are partially ionized and the interaction between ionized particles and neutral particles has important consequences on the magneto-thermodynamics of these layers. The partial ionization effects are treated using generalized Ohm's law, i.e. we consider the Hall term and the ambipolar diffusion (Pedersen dissipation) in the induction equation. The interaction between the different species affects the modelled atmosphere as follows: (i) the ambipolar diffusion dissipates magnetic energy and increases the minimum temperature in the chromosphere and (ii) the upper chromosphere may get heated and expanded over a greater range of heights. These processes reveal appreciable differences between the modelled atmospheres of simulations with and without ion–neutral interaction effects.

On Magnetic Helicity and Field-Aligned Currents in the Polar Ionosphere

2021 ◽  
Author(s):  
Paola De Michelis ◽  
Giuseppe Consolini ◽  
Tommaso Alberti ◽  
Vincenzo Carbone ◽  
Roberta Tozzi ◽  
...  
Keyword(s):  
Coarse Grained ◽  
Magnetic Helicity ◽  
Magnetic Data ◽  
Small Scale ◽  
Polar Ionosphere ◽  
Clear Link ◽  
High Latitude Ionosphere ◽  
Field Aligned Current ◽  
Field Lines

<p>Magnetic helicity, which is a measure of twist and linkage of magnetic field lines, is a useful quantity to investigate some processes occurring in space plasmas. In particular, there is a strong link between magnetic helicity, magnetic flux structures, turbulence and dissipation. We investigate the connection between the reduced magnetic helicity and the structure of field-aligned currents in the high-latitude ionosphere using high resolution (50 Hz) magnetic data collected on board the ESA Swarm constellation. We show the existence of a clear link between the multiscale coarse-grained structure of reduced magnetic helicity and the field-aligned currents. This finding strongly supports the idea that turbulence processes might be at the origin of the observed small-scale current structures. A discussion of the relevance of our results in the framework of the filamentary nature of the field-aligned current is also presented.</p><p><span>This work is supported by Italian PNRA under contract </span>PNRA18_00289-A “Space weather in Polar Ionosphere: the Role of Turbulence ".</p>

Rethinking Economic Structure: Exploring the Role of the Small Firm and Self-Employment in the British Economy

1990 ◽  
Vol 4 (5) ◽  
pp. 125-146 ◽  
Author(s):  
James Curran
Keyword(s):  
Economic Restructuring ◽  
Economic Structure ◽  
Small Scale ◽  
Economic Activities ◽  
Self Employment ◽  
The Social ◽  
Wide Range ◽  
Industrial Societies ◽  
Theoretical Issues

Dominant sociological interpretations of the economic structures of industrial societies have long neglected the role of small scale economic activities. However, current rethinking, stimulated by attempts to explain economic restructuring in the 1980s, appears to offer petty capitalism and self-employment a more important role in the economy. Several versions of economic restructuring theory are examined critically and argued to continue to offer an inadequate account of the role of small scale enterprise in the economy and especially of the social reality of small scale enterprise ownership, organisational patterns and employment. Conceptual and theoretical issues relevant to a more direct focus on small scale economic activities are explored together with a review of studies of a wide range of aspects of such activities. The paper ends by arguing for the continuing importance of small scale economic activities in industrial societies and the need for analyses of economic restructuring and, more fundamentally economic sociology generally, to incorporate a proper recognition of small scale economic activities and self-employment.

scholarly journals A small-scale EUV jet in the quiet Sun region

2012 ◽  
Vol 8 (S294) ◽  
pp. 555-559
Author(s):  
Junchao Hong ◽  
Yunchun Jiang ◽  
Ruisheng Zheng ◽  
Yi Bi
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Reconnection ◽  
Solar Atmosphere ◽  
Extreme Ultraviolet ◽  
Small Scale ◽  
Quiet Sun ◽  
Filament Channel ◽  
Field Lines ◽  
Using Data

AbstractSolar jets are typical proxies of small-scale magnetic reconnection events in the solar atmosphere. In this paper, we observe a small-scale jet in a solar quiet region, using data from SDO/Atmospheric Imaging Assembly (AIA), Helioseismic and Magnetic Imager (HMI), with supplemental data from STEREO/EUVI. From HMI magnetograms and calculated photospheric flows, we find that the jet is related to the interaction between unipolar network fields and emerging internetwork bipoles at the boundary of a supergranular cell. In AIA extreme-ultraviolet images, the jet actually includes two successive plasma ejections along different directions. The first ejection follows a distorted path which guides plasma into a small filament channel nearby. However, the second one shot straight along another direction that is parallel with extrapolated potential magnetic field lines on the local. According to these observations, we advocate that during the jet eruption new emerging magnetic fields are reconnecting at the edge of the supergranular cell with different kinds of ambient fields from low (magnetic canopy) to high (high-reaching loops) to allow the occurrence of successive ejections along different directions.

Influence of Magnetic Fields on Solar Hydrodynamics: Experimental Results

1977 ◽  
Vol 36 ◽  
pp. 143-180 ◽  
Author(s):  
J.O. Stenflo
Keyword(s):  
Solar Activity ◽  
Energy Balance ◽  
Magnetic Fields ◽  
Solar Atmosphere ◽  
General Problem ◽  
Solar Rotation ◽  
Active Regions ◽  
Physical Conditions ◽  
Dynamic Phenomena

It is well-known that solar activity is basically caused by the Interaction of magnetic fields with convection and solar rotation, resulting in a great variety of dynamic phenomena, like flares, surges, sunspots, prominences, etc. Many conferences have been devoted to solar activity, including the role of magnetic fields. Similar attention has not been paid to the role of magnetic fields for the overall dynamics and energy balance of the solar atmosphere, related to the general problem of chromospheric and coronal heating. To penetrate this problem we have to focus our attention more on the physical conditions in the ‘quiet’ regions than on the conspicuous phenomena in active regions.

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