Polar surges and macrospicules

Georgakilas, A.; Koutchmy, S.; Christopoulou, E. B.

doi:10.1051/0004-6361:20010228

Cited by 9 publications

(14 citation statements)

References 15 publications

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“…We note that this assumption is modelindependent but may lead to an underestimation of the deduced velocities (Labrosse et al 2010). The velocities are readily deduced from this calibration curve, in agreement with the calibration of Georgakilas et al (2001) who used the same UBF mode. Figures 13 and 14 show the Hα summed wings intensity sequence, and Figs.…”

Section: Dst Dataset Propertiessupporting

confidence: 77%

“…The wing intensity is the sum of the signals obtained in the red and blue wings. The Doppler velocity is obtained using the following method (Malherbe et al 1997;Georgakilas et al 2001): an Hα reference centre-disc profile (Delbouille et al 1973) 3 is convolved with a Gaussian profile with a 0.24 Å FWHM, corresponding to the width of the filter used for the observations. This profile is shifted by several steps Δλ = FWHM 2 .…”

Section: Dst Dataset Propertiesmentioning

confidence: 99%

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Oscillatory motions observed in eruptive filaments

Bocchialini

Baudin

Koutchmy

et al. 2011

A&A

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Context. The origin of the variable component of the solar wind is of great intrinsic interest for heliophysics and spaceweather, e.g. the initiation of coronal mass ejections and the problem of mass loss of all stars. It is also related to the physics of coronal neutral sheets and streamers, which occur above lines of magnetic polarity reversal. Filaments and prominences correspond to the cool coronal component of these regions. Aims. We examine the dynamical behaviour of these structures where reconnection and dissipation of magnetic energy in the turbulent plasma are occurring. The link between the observed oscillatory motions and the eruption occurrence is investigated in detail for two different events. Methods. Two filaments were analysed using two different datasets: time series of spectra using a transition region line (He I at 584.33 Å) and a coronal line (Mg X at 609.79 Å) measured with CDS on-board SOHO, observed on May 30, 2003, and time series of intensity and velocity images from the NSO/Dunn Solar Telescope in the Hα line on September 18, 1994 for the other. The oscillatory content was investigated using Fourier transform and wavelet analysis and compared to different models. Results. In both filaments, oscillations are clearly observed, in intensity and velocity in the He I and Mg X lines, in velocity in Hα, with similar periods from a few minutes up to 80 min, with a main range from 20 to 30 min, simultaneously with eruptions. Both filaments exhibit vertical oscillating motions. For the filament observed in the UV (He I and Mg X lines), we provide evidence of damped velocity oscillations, and for the filament observed in the visible (Hα line), we provide evidence that parts of the filament are oscillating, while the filament is moving over the solar surface, before its disappearance.

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Section: Dst Dataset Propertiessupporting

confidence: 77%

Section: Dst Dataset Propertiesmentioning

confidence: 99%

Oscillatory motions observed in eruptive filaments

Bocchialini

Baudin

Koutchmy

et al. 2011

A&A

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“…It immediately comes to mind that it maybe possibly comparable to surge-like events observed in polar regions, which are also called macro-spicules (e.g., Georgakilas et al 2001). Because torsional motion occurs simultaneously and close to other components (Figs.…”

Section: Discussionmentioning

confidence: 83%

“…Some similarity possibly exists with Ellerman bombs (moustaches) that usually appear near sunspots at lower latitudes. These cool plasma jets are a kind of active small prominence, usually observed in Hα at ground-based observatories (Georgakilas et al 1999(Georgakilas et al , 2001) and known for a long time from eclipse observations (e.g., Fig. 140, p. 389 in Secchi 1875), although space observations, such as with extreme-ultraviolet (EUV) telescopes, also detect surges.…”

Section: Discussionmentioning

confidence: 99%

Alfvénic waves in polar spicules

Tavabi

Koutchmy

Ajabshirizadeh

et al. 2014

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Context. For investigating spicules from the photosphere to coronal heights, the new Hinode/SOT long series of high-resolution observations from space taken in CaII H line emission offers an improved way to look at their remarkable dynamical behavior using images free of seeing effects. They should be put in the context of the huge amount of already accumulated material from groundbased instruments, including high-resolution spectra of off-limb spicules. Aims. Both the origin of the phenomenon and the significance of dynamical spicules for the heating above the top of the photosphere and the fuelling of the chromospheric and the transition region need more investigation, including of the possible role of the associated magnetic waves for the corona higher up. Methods. We analyze in great detail the proper transverse motions of mature and tall polar region spicules for different heights, assuming that there might be Helical-Kink waves or Alfvénic waves propagating inside their multicomponent substructure, by interpreting the quasi-coherent behavior of all visible components presumably confined by a surrounding magnetic envelop. We concentrate the analysis on the taller CaII spicules more relevant for coronal heights and easier to measure. Two-dimensional velocity maps of proper motion were computed for the first time using a correlation tracking technique based on FFTs and cross-correlation function with a 2nd-order-accuracy Taylor expansion. Highly processed images with the popular mad-max algorithm were first prepared to perform this analysis. The locations of the peak of the cross-correlation function were obtained with subpixel accuracy. Results. The surge-like behavior of solar polar region spicules supports the untwisting multicomponent interpretation of spicules exhibiting helical dynamics. Several tall spicules are found with (i) upward and downward flows that are similar at lower and middle levels, the rate of upward motion being slightly higher at high levels; (ii) the left-and righthand velocities are also increasing with height; (iii) a large number of multicomponent spicules show shearing motion of both left-and righthanded senses occurring simultaneously, which might be understood as twisting (or untwisting) threads. The number of turns depends on the overall diameter of the structure made of components and changes from at least one turn for the smallest structure to at most two or three turns for surge-like broad structures. The curvature along the spicule corresponds to a low turn number similar to a transverse kink mode oscillation along the threads.

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“…In order to compute the line-of-sight velocity from only two opposite Hα wing filtergrams, estimations of the optical depth at line center and the Doppler width are further needed (see Georgakilas et al 1990). Bray and others authors successfully applied the method for studying the physical properties of various chromospheric features (Bray 1973a(Bray , 1974Georgakilas et al 1990;Suematsu et al 1995;Malherbe et al 1997;Georgakilas et al 2001). We applied the above method in order to compute line-of-sight velocities from the Hα ± 0.35 Å, Hα ± 0.5 Å and Hα ± 0.75 Å filtergrams.…”

Section: Computation Of Line-of-sight Velocitiesmentioning

confidence: 99%

Chromospheric Evershed flow

Georgakilas

Christopoulou

Skodras

et al. 2003

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Abstract. We studied the chromospheric Evershed flow from filtergrams obtained at nine wavelengths along the Hα profile. We computed line-of-sight velocities based on Becker's cloud model and we determined the components of the flow velocity vector as a function of distance from the center of the sunspot, assuming an axial symmetry of both the spot and the flow. We found that the flow velocity decreases with decreasing height and that the maximum of the velocity shifts towards the inner penumbral boundary. The flow related to some fibrils deviates significantly from the average Evershed flow. The profile of the magnitude of the flow velocity as a function of distance from the spot center, indicates that the velocity attains its maximum value in the downstream part of the flow channels (assumed to have the form of a loop). This behavior can be understood in terms of a critical flow that pass from subsonic to supersonic near the apex of the loop, attains its higher velocity at the downstream part of the loop and finally relaxes to subsonic through a tube shock. We computed the average flow vector from segmented line-of-sight velocity maps, excluding bright or dark fibrils alternatively. We found that the radial component of the velocity does not show a significant difference, but the magnitude of the vertical component of the velocity related to dark fibrils is higher than that related to bright fibrils.

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Polar surges and macrospicules

Cited by 9 publications

References 15 publications

Oscillatory motions observed in eruptive filaments

Oscillatory motions observed in eruptive filaments

Alfvénic waves in polar spicules

Chromospheric Evershed flow

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