Observations of Ellerman bombs in H ?

Zachariadis, Theodoros; Alissandrakis, C. E.; Banos, G.

doi:10.1007/bf00214163

Cited by 38 publications

(47 citation statements)

References 14 publications

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“…Our results are in agreement with previous studies reporting that the spatial distribution of EBs is not random or homogeneous (Vorpahl & Pope 1972;Bruzek 1972;Zachariadis et al 1987). A detailed study of the photospheric patterns for each of the three areas shown in Figure 2, follows in x 4.2.…”

Section: Occurrence Rates and Spatial Distribution Of Ebssupporting

confidence: 92%

“…Although EBs, or moustaches, were not explicitly cited in that work, the properties of those H brightenings were indicative of EBs. Other studies found several EBs at the boundaries of welldefined magnetic structures (Roy & Leparskas 1973;Dara et al 1997), related to dipolar emerging flux (Zachariadis et al 1987) and moving magnetic features (Nindos & Zirin 1998).…”

Section: Introductionmentioning

confidence: 91%

“…This average is significantly lower compared to previous reports. Zachariadis, Alissandrakis, & Banos (1987) reported an average contrast of $27%, while Nindos & Zirin (1998) reported a mean value of $29%-31%. We have defined several contrast thresholds, or background contrasts, in the range [0.05, 0.20].…”

Section: Occurrence Rates and Spatial Distribution Of Ebsmentioning

confidence: 99%

“…They generally occur in areas of flux emergence and strong magnetic fields, such as the vicinity of the penumbra around isolated sunspots and the interspot areas of new and dynamic emerging flux regions, beneath the expanding arch filament system (AFS). Zachariadis, Alissandrakis, & Banos (1987) estimated a mean occurrence rate of about 1.5 EBs minute À1 in an area of size 18 00 Â 24 00 . The typical sizes of EBs are of the order 1 00 .…”

Section: Introductionmentioning

confidence: 99%

“…Bruzek (1972) and Vorpahl & Pope (1972), however, reported that certain EBs could be visible for times exceeding 1 hr. The estimation of EB durations depends critically on the temporal resolution (cadence) of the observing instrument, since EBs often tend to recur at approximately the same locations (Vorpahl & Pope 1972;Bruzek 1972;Zachariadis et al 1987). The generally accepted mean lifetime of EBs is 10-14 minutes (Roy & Leparskas 1973;Kurokawa et al 1982;Payne 1993;Nindos & Zirin 1998).…”

Section: Introductionmentioning

confidence: 99%

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Statistics, Morphology, and Energetics of Ellerman Bombs

Georgoulis¹,

Rust²,

Bernasconi³

et al. 2002

ApJ

199

287

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We investigate the statistical properties of Ellerman bombs in the dynamic emerging flux region NOAA Active Region 8844, underneath an expanding arch filament system. High-resolution chromospheric H filtergrams (spatial resolution 0>8), as well as photospheric vector magnetograms (spatial resolution 0>5) and Dopplergrams, have been acquired by the balloon-borne Flare Genesis Experiment. H observations reveal the first '' seeing-free '' data set on Ellerman bombs and one of the largest samples of these events. We find that Ellerman bombs occur and recur in preferential locations in the low chromosphere, either above or in the absence of photospheric neutral magnetic lines. Ellerman bombs are associated with photospheric downflows, and their loci follow the transverse mass flows on the photosphere. They are small-scale events, with typical size 1>8 Â 1>1 , but this size depends on the instrumental resolution. A large number of Ellerman bombs are probably undetected, owing to limited spatial resolution. Ellerman bombs occur in clusters that exhibit fractal properties. The fractal dimension, with an average value $1.4, does not change significantly in the course of time. Typical parameters of Ellerman bombs are interrelated and obey power-law distribution functions, as in the case of flaring and subflaring activity. We find that Ellerman bombs may occur on separatrix, or quasi-separatrix, layers, in the low chromosphere. A plausible triggering mechanism of Ellerman bombs is stochastic magnetic reconnection caused by the turbulent evolution of the low-lying magnetic fields and the continuous reshaping of separatrix layers. The total energies of Ellerman bombs are estimated in the range (10 27 , 10 28 ) ergs, the temperature enhancement in the radiating volume is $2 Â 10 3 K, and the timescale of radiative cooling is short, of the order of a few seconds. The distribution function of the energies of Ellerman bombs exhibits a power-law shape with an index $À2.1. This suggests that Ellerman bombs may contribute significantly to the heating of the low chromosphere in emerging flux regions.

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Section: Occurrence Rates and Spatial Distribution Of Ebssupporting

confidence: 92%

Section: Introductionmentioning

confidence: 91%

Section: Occurrence Rates and Spatial Distribution Of Ebsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Statistics, Morphology, and Energetics of Ellerman Bombs

Georgoulis¹,

Rust²,

Bernasconi³

et al. 2002

ApJ

199

287

View full text Add to dashboard Cite

show abstract

A possible mechanism governing the production and evolution of Ellerman bombs

1996

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A hydrodynamic-magnetofluid hybrid analysis of lower chromospheric shear flows in the Sun may explain the occurrence and time development of Ellerman bombs. The analysis assumes that the erupting material forming the bomb is driven initially by the Kelvin-Helmholtz fluid instability applied to the interface between two atmospheric fluid layers, characterized by a steep density change across the boundary and driven by flow fields around sunspots. The ensuing instability eventually evolves into a magnetofluid phenomenon by virtue of the trapping and bending of the interfacial magnetic field, giving rise to a dense globule of material entering, and persisting in, the upper layers and due to Ohmic dissipation having a significantly enhanced temperature compared with ambient material.

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Mass motions associated with H? active region arch structures

1990

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We have studied mass motions associated with active region arch structures from observations of a developing active region near the center of the solar disk. We present a method for the computation of the line-of-sight velocity from photographs at Hc~ + 0.5 under the assumption of Beckers' cloud model and reasonable assumptions about the Doppler width and optical depth of the arches. Some arches show motions typical to arch filaments (the material moves towards the observer near the apex of the arch and away from the observer near the footpoints), while in others the velocity field is more complex. Assuming a symmetric loop, we reconstructed the velocity vector along an arch filament. The results are consistent with the picture where material is draining out of the filament while the whole structure is ascending with a velocity near that of the apex, which does not exceed 10 km s -1. The motion is systematically slower than expected from a free-fail model.

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Observations of Ellerman bombs in H ?

Cited by 38 publications

References 14 publications

Statistics, Morphology, and Energetics of Ellerman Bombs

Statistics, Morphology, and Energetics of Ellerman Bombs

A possible mechanism governing the production and evolution of Ellerman bombs

Mass motions associated with H? active region arch structures

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