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Bumba, V.; Kopecký, M.

doi:10.1007/bf01557106

Cited by 7 publications

(11 citation statements)

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“…Our LOS velocities are similar to those observed by Bumba (1960), Severny (1960) and Bellot Rubio (2010), and greater than those reported by, e.g., Bellot Rubio et al (2004) and Ichimoto et al (2007). We find differences with the results of del Toro Iniesta et al (2001), who detected Evershed supersonic downflows concentrated in cold magnetic tubes with LOS velocities up to 16 km s −1 .…”

Section: Comparison With Previous Studiescontrasting

confidence: 56%

“…The existence of strong Evershed downflows in the penumbra is suspected since long. They were first reported by Bumba (1960) as line flags, where the line is not shifted as a whole but instead has a very strong asymmetry (flag). Such extreme cases of line asymmetries were interpreted in terms of a superposition of two unresolved structures: an almost unshifted strong component, which corresponds to the "mean" Evershed effect (Evershed 1909), and a weaker strongly displaced component (satellite) where the line-of-sight (hereafter, LOS) velocity reaches up to 7-8 km s −1 (Severny 1960, Servajean 1961Maltby 1964;Stellmacher & Wiehr 1971;Wiehr 1995).…”

Section: Introductionmentioning

confidence: 99%

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Properties of Supersonic Evershed Downflows

Pozuelo

Rubio

Rodríguez

2016

ApJ

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We study supersonic Evershed downflows in a sunspot penumbra by means of high spatial resolution spectropolarimetric data acquired in the Fe I 617.3 nm line with the CRISP instrument at the Swedish 1-m Solar Telescope. Physical observables, such as Dopplergrams calculated from line bisectors and Stokes V zero-crossing wavelengths, and Stokes V maps in the far red wing, are used to find regions where supersonic Evershed downflows may exist. We retrieve the LOS velocity and the magnetic field vector in these regions using two-component inversions of the observed Stokes profiles with the help of the SIR code. We follow these regions during their lifetime to study their temporal behavior. Finally, we carry out a statistical analysis of the detected supersonic downflows to characterize their physical properties. Supersonic downflows are contained in compact patches moving outward, which are located in the mid and outer penumbra. They are observed as bright, roundish structures at the outer end of penumbral filaments that resemble penumbral grains. The patches may undergo fragmentations and mergings during their lifetime, even some of them are recurrents. Supersonic downflows are associated with strong and rather vertical magnetic fields with a reversed polarity compared to that of the sunspot. Our results suggest that downflows returning back to the solar surface with supersonic velocities are abruptly stopped in dense deep layers and produce a shock. Consequently, this shock enhances the temperature and is detected as a bright grain in the continuum filtergrams, which could explain the existence of outward moving grains in the mid and outer penumbra.

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Section: Comparison With Previous Studiescontrasting

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Properties of Supersonic Evershed Downflows

Pozuelo

Rubio

Rodríguez

2016

ApJ

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“…Bumba & Křiviský (1959), who introduced the term "preflares", were the first to address this topic. Reviews of early studies for such flare precursors can be found in Martin et al (1980) and Van Hoven & Hurford (1984).…”

Section: Introductionmentioning

confidence: 99%

X-ray precursors to flares and filament eruptions

Chifor¹,

Tripathi²,

Mason³

et al. 2007

A&A

103

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Aims. To study preflare X-ray brightenings as diagnostics of the destabilisation of flare-associated erupting filaments/prominences. Methods. We combine new observations from the Transition Region and Coronal Explorer (TRACE) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), as well as revisit events reported in the literature to date, in order to scrutinise the preflare activity during eight flare-associated filament eruptions. Results. The preflare activity occurs in the form of discrete, localised X-ray brightenings observed between 2 and 50 min before the impulsive phase of the flare and filament acceleration. These transient preflare brightenings are situated on or near (within 10 of) the polarity inversion line (PIL), coincident with emerging and/or canceling magnetic flux. The filaments begin to rise from the location of the preflare brightenings. In five out of eight events, the preflare brightenings were observed beneath the filament channel, close to the filament footpoint first observed to rise. Both thermal and nonthermal hard X-ray emissions during the preflare enhancement were detected with RHESSI, suggesting that both plasma heating and electron acceleration occurred at this time. The main energy release during the impulsive phase of the flare is observed close to (within 50 of) the preflare brightenings. The fast-rise phase of the filament eruption starts at the same time as the onset of the main flare or up to 5 min later. Conclusions. The preflare brightenings are precursors to the flare and filament eruption. These precursors represent distinct, localised instances of energy release, rather than a gradual energy release prior to the main flare. The X-ray precursors represent clearly observable signatures in the early stages of the eruption. Together with the timing of the filament fast-rise at or after the main flare onset, the X-ray precursors provide evidence for a tether-cutting mechanism initially manifested as localised magnetic reconnection being a common trigger for both flare emission and filament eruption.

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“…First, one can assume the existence of unresolved structure when analyzing the data, in particular when interpreting spectral line asymmetries (e.g., Bumba 1960;Grigorjev & Katz 1972;Golovko 1974;Sánchez Almeida & Lites 1992;Wiehr 1995;Solanki & Montavon 1993;Bellot Rubio 2004;Sánchez Almeida 2005). Via line fitting and with proper modeling, this indirect technique allows us to infer the physical properties of unresolved structures.…”

Section: Introductionmentioning

confidence: 99%

High‐Resolution Proper Motions in a Sunspot Penumbra

Márquez

Alméida

Bonet

2006

ApJ

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Local correlation tracking techniques are used to measure proper motions in a series of high angular resolution ($0B1) penumbra images. If these motions trace true plasma motions, then we have detected converging flows that arrange the plasma in long narrow filaments cospatial with dark penumbral filaments. Assuming that these flows are stationary, the vertical stratification of the atmosphere and the conservation of mass suggest downflows in the filaments on the order of 200 m s À1 . The association between downflows and dark features may be a sign of convection, as it happens with the nonmagnetic granulation. Insufficient spatial resolution may explain why the estimated vertical velocities are not fast enough to supply the radiative losses of penumbrae.

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Cited by 7 publications

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Properties of Supersonic Evershed Downflows

Properties of Supersonic Evershed Downflows

X-ray precursors to flares and filament eruptions

High‐Resolution Proper Motions in a Sunspot Penumbra

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