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Joey W. Rogers

Bio: Joey W. Rogers is an academic researcher from National Science Foundation. The author has contributed to research in topics: Sunspot & Solar observatory. The author has an hindex of 2, co-authored 2 publications receiving 154 citations. Previous affiliations of Joey W. Rogers include Association of Universities for Research in Astronomy.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors used the chromospheric full-disk Hα observations to study the chirality of 2310 filaments from 2000-2001 and found that 80.2% (558 out of 696) of quiescent filaments in the northern hemisphere are dextral and 85.5% (633 out of 740) of filament in the southern hemisphere are sinistral, in agreement with the well-known hemispheric helicity rule.
Abstract: We use the chromospheric full-disk Hα observations to study the chirality of 2310 filaments from 2000-2001. For each filament, we identify the spine and its barbs and determine the filament chirality as fraction of dextral/sinistral barbs of the total number of barbs. We find that 80.2% (558 out of 696) of quiescent filaments in the northern hemisphere are dextral and 85.5% (633 out of 740) of filaments in southern hemisphere are sinistral, in agreement with the well-known hemispheric helicity rule. Our data also show that the active-region filaments follow the same rule, though the hemispheric dependence is weaker: 74.9% (338 out of 451) of active-region filaments in the northern hemisphere are dextral, and 76.7% (297 out of 387) of filaments in the southern hemisphere are sinistral. We show that quiescent filaments formed on leading and returning arms of the same switchback exhibit the same chirality. We also investigate a possible change in the hemispheric rule with polarity reversal of the polar field, and we find no such change.

141 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the properties of 897 superpenumbral fibrils using Hα Big Bear Solar Observatory (BBSO) and photospheric magnetic field National Solar Observatory/Kitt Peak (NSO/KP) data of 139 sunspots between 2000 July and 2001 April.
Abstract: We study properties of 897 superpenumbral fibrils using Hα Big Bear Solar Observatory (BBSO) and photospheric magnetic field National Solar Observatory/Kitt Peak (NSO/KP) data of 139 sunspots between 2000 July and 2001 April. From this low-resolution data, we find that about one-third of all superpenumbral fibrils begin inside the penumbra. The typical length of fibrils is 2.7 times the sunspot white-light penumbral radius. A majority of the fibrils are curved, i.e., 67% of them exhibit bow-extent/footpoint separation greater than 0.1. Both clockwise and counterclockwise fibrils are typically present within the same superpenumbra. We show that the topology of fibrils is clearly affected by distribution of magnetic fields around the sunspot.

17 citations


Cited by
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Journal ArticleDOI
TL;DR: The current understanding of solar flares, mainly focused on magnetohydrodynamic (MHD) processes responsible for producing a flare, can be found in this article, where the authors present a review of the models proposed to explain the physical mechanism of flares, giving an comprehensive explanation of the key processes.
Abstract: This paper outlines the current understanding of solar flares, mainly focused on magnetohydrodynamic (MHD) processes responsible for producing a flare. Observations show that flares are one of the most explosive phenomena in the atmosphere of the Sun, releasing a huge amount of energy up to about 1032 erg on the timescale of hours. Flares involve the heating of plasma, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes for producing a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), local enhancement of electric current in the corona (formation of a current sheet), and rapid dissipation of electric current (magnetic reconnection) that causes shock heating, mass ejection, and particle acceleration. The evolution toward the onset of a flare is rather quasi-static when free energy is accumulated in the form of coronal electric current (field-aligned current, more precisely), while the dissipation of coronal current proceeds rapidly, producing various dynamic events that affect lower atmospheres such as the chromosphere and photosphere. Flares manifest such rapid dissipation of coronal current, and their theoretical modeling has been developed in accordance with observations, in which numerical simulations proved to be a strong tool reproducing the time-dependent, nonlinear evolution of a flare. We review the models proposed to explain the physical mechanism of flares, giving an comprehensive explanation of the key processes mentioned above. We start with basic properties of flares, then go into the details of energy build-up, release and transport in flares where magnetic reconnection works as the central engine to produce a flare.

677 citations

Journal ArticleDOI
TL;DR: In this article, the authors focus on non-eruptive solar prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) magneto-hydrodynamic (MHD) waves in prominence and (4) the formation and large-scale patterns of the filament channels in which promine are located.
Abstract: Observations and models of solar prominences are reviewed. We focus on non-eruptive prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and large-scale patterns of the filament channels in which prominences are located. Finally, several outstanding issues in prominence research are discussed, along with observations and models required to resolve them.

656 citations

Journal ArticleDOI
TL;DR: In this article, a series of three-dimensional numerical simulations of MHD convection within rotating spherical shells using anelastic spherical harmonic (ASH) code on massively parallel supercomputers is presented.
Abstract: The operation of the solar global dynamo appears to involve many dynamical elements, including the generation of fields by the intense turbulence of the deep convection zone, the transport of these fields into the tachocline region near the base of the convection zone, the storage and amplification of toroidal fields in the tachocline by differential rotation, and the destabilization and emergence of such fields due to magnetic buoyancy. Self-consistent magnetohydrodynamic (MHD) simulations that realistically incorporate all of these processes are not yet computationally feasible, although some elements can now be studied with reasonable fidelity. Here we consider the manner in which turbulent compressible convection within the bulk of the solar convection zone can generate large-scale magnetic fields through dynamo action. We accomplish this through a series of three-dimensional numerical simulations of MHD convection within rotating spherical shells using our anelastic spherical harmonic (ASH) code on massively parallel supercomputers. Since differential rotation is a key ingredient in all dynamo models, we also examine here the nature of the rotation profiles that can be sustained within the deep convection zone as strong magnetic fields are built and maintained. We find that the convection is able to maintain a solar-like angular velocity profile despite the influence of Maxwell stresses, which tend to oppose Reynolds stresses and thus reduce the latitudinal angular velocity contrast throughout the convection zone. The dynamo-generated magnetic fields exhibit a complex structure and evolution, with radial fields concentrated in downflow lanes and toroidal fields organized into twisted ribbons that are extended in longitude and achieve field strengths of up to 5000 G. The flows and fields exhibit substantial kinetic and magnetic helicity although systematic hemispherical patterns are only apparent in the former. Fluctuating fields dominate the magnetic energy and account for most of the back-reaction on the flow via Lorentz forces. Mean fields are relatively weak and do not exhibit systematic latitudinal propagation or periodic polarity reversals as in the Sun. This may be attributed to the absence of a tachocline, i.e., a penetrative boundary layer between the convection zone and the deeper radiative interior possessing strong rotational shear. The influence of such a layer will await subsequent studies.

540 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a review of the present day understanding of the Sun's global photospheric and coronal magnetic fields from both observational and theoretical viewpoints, focusing mainly on solar magnetic fields.
Abstract: In this review, our present day understanding of the Sun's global photospheric and coronal magnetic fields is discussed from both observational and theoretical viewpoints. Firstly, the large-scale properties of photospheric magnetic fields are described, along with recent advances in photospheric magnetic flux transport models. Following this, the wide variety of theoretical models used to simulate global coronal magnetic fields are described. From this, the combined application of both magnetic flux transport simulations and coronal modeling techniques to describe the phenomena of coronal holes, the Sun's open magnetic flux and the hemispheric pattern of solar filaments is discussed. Finally, recent advances in non-eruptive global MHD models are described. While the review focuses mainly on solar magnetic fields, recent advances in measuring and modeling stellar magnetic fields are described where appropriate. In the final section key areas of future research are identified.

171 citations

Journal ArticleDOI
TL;DR: In this paper, an active-region dextral filament was modeled as a double-decker configuration with two branches separated in height by about 13 meters, as inferred from three-dimensional reconstruction by combining SDO and STEREO-B observations.
Abstract: We study an active-region dextral filament that was composed of two branches separated in height by about 13 Mm, as inferred from three-dimensional reconstruction by combining SDO and STEREO-B observations. This "double-decker" configuration sustained for days before the upper branch erupted with a GOES-class M1.0 flare on 2010 August 7. Analyzing this evolution, we obtain the following main results. (1) During the hours before the eruption, filament threads within the lower branch were observed to intermittently brighten up, lift upward, and then merge with the upper branch. The merging process contributed magnetic flux and current to the upper branch, resulting in its quasi-static ascent. (2) This transfer might serve as the key mechanism for the upper branch to lose equilibrium by reaching the limiting flux that can be stably held down by the overlying field or by reaching the threshold of the torus instability. (3) The erupting branch first straightened from a reverse S shape that followed the polarity inversion line and then writhed into a forward S shape. This shows a transfer of left-handed helicity in a sequence of writhe-twist-writhe. The fact that the initial writhe is converted into the twist of the flux rope excludes the helical kink instability as the trigger process of the eruption, but supports the occurrence of the instability in the main phase, which is indeed indicated by the very strong writhing motion. (4) A hard X-ray sigmoid, likely of coronal origin, formed in the gap between the two original filament branches in the impulsive phase of the associated flare. This supports a model of transient sigmoids forming in the vertical flare current sheet. (5) Left-handed magnetic helicity is inferred for both branches of the dextral filament. (6) Two types of force-free magnetic configurations are compatible with the data, a double flux rope equilibrium and a single flux rope situated above a loop arcade.

164 citations