Line-of-sight effects on observability of kink and sausage
modes in coronal structures with imaging telescopes

Cooper, Fenwick; Nakariakov, V. M.; Tsiklauri, David

doi:10.1051/0004-6361:20021556

Cited by 80 publications

(74 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…4, we recall that slow mode waves (slow magnetoacoustic) are, however, likely to be responsible for the oscillations between 2-8 mHz concentrated in the plage regions. We note that fast kink waves, although essentially noncompressive, may potentially be seen in radiance measurements from the change they can cause on the loop length (Wang & Solanki 2004) or, indeed, just from the angle at which they are observed (Cooper et al 2003). Taking this into account, we can consider instead that the oscillations we see in the active region loop are fast magnetoacoustic waves.…”

Section: Resultsmentioning

confidence: 91%

On oscillations found in an active region with EIS on Hinode

O’Shea

Doyle

2008

A&A

View full text Add to dashboard Cite

Aims. Using temporal series (40 slot) data in the Fe xii 195 Å line from the extreme-ultraviolet imaging spectrometer (EIS) on board the Hinode satellite, we seek to carry out a statistical study of oscillations in an active region. Methods. Using wavelet techniques, we measure the frequency and duration of oscillations found in the time series data. Stokes I and V data from Hinode's SOT are used to measure photospheric magnetic fields, while an EIS raster is used to provide estimates of LOS velocity and electron density. The measured frequencies are displayed as maps in different bands to aid their analysis.Results. Oscillations over a broad range of frequencies (2-154 mHz) are found throughout the active region at the temperature of Fe xii (log T = 6.1 K). Oscillations with frequencies between 2-8 mHz are concentrated in bright plage areas, while oscillations of higher frequency preferentially group at the edges of these areas. Evidence is found for harmonics on the boundary of the active region loop, indicating the presence of standing waves. From a measurement of the lengths and electron density of loops appearing in our active region field-of-view (FOV), together with a knowledge of the periods (frequencies) of the oscillations within the area of these loops, we find a magnetic field value of between 12.2 ± 2.08−18.9 ± 3.40 G, assuming standing fast kink waves. Conclusions. We conclude that waves, which the observed oscillations are signatures of, are common in the active region studied, over a broad range of frequencies. The change in the distribution of the oscillations present at frequencies less than 8 mHz and those at all frequencies above this indicates a variation of the wave mode with frequency, e.g., possibly from slow magnetoacoustic waves in the bright plage regions to fast magnetoacoustic waves at the boundaries of these regions. The preference for higher frequency oscillations to cluster on the edges of regions of high magnetic field is considered indicative of resonant absorption. Based on our measurements of magnetic field, we conclude that the oscillations found by us in the active region loop are fast kink waves.

show abstract

Section: Resultsmentioning

confidence: 91%

On oscillations found in an active region with EIS on Hinode

O’Shea

Doyle

2008

A&A

View full text Add to dashboard Cite

show abstract

“…However, if this is satisfied the subsequent estimates of ρ 0 /ρ e and are not affected by LOS integration effects (e.g. Cooper et al 2003;Viall & Klimchuk 2013).…”

Section: Discussionmentioning

confidence: 94%

Coronal loop seismology using damping of standing kink oscillations by mode coupling

Pascoe

Goddard

Nisticò

et al. 2016

A&A

Self Cite

View full text Add to dashboard Cite

Context. Kink oscillations of solar coronal loops are frequently observed to be strongly damped. The damping can be explained by mode coupling on the condition that loops have a finite inhomogeneous layer between the higher density core and lower density background. The damping rate depends on the loop density contrast ratio and inhomogeneous layer width. Aims. The theoretical description for mode coupling of kink waves has been extended to include the initial Gaussian damping regime in addition to the exponential asymptotic state. Observation of these damping regimes would provide information about the structuring of the coronal loop and so provide a seismological tool. Methods. We consider three examples of standing kink oscillations observed by the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) for which the general damping profile (Gaussian and exponential regimes) can be fitted. Determining the Gaussian and exponential damping times allows us to perform seismological inversions for the loop density contrast ratio and the inhomogeneous layer width normalised to the loop radius. The layer width and loop minor radius are found separately by comparing the observed loop intensity profile with forward modelling based on our seismological results. Results. The seismological method which allows the density contrast ratio and inhomogeneous layer width to be simultaneously determined from the kink mode damping profile has been applied to observational data for the first time. This allows the internal and external Alfvén speeds to be calculated, and estimates for the magnetic field strength can be dramatically improved using the given plasma density. Conclusions. The kink mode damping rate can be used as a powerful diagnostic tool to determine the coronal loop density profile. This information can be used for further calculations such as the magnetic field strength or phase mixing rate.

show abstract

“…During the observation, several distinct loop bundles appear, experiencing some transverse displacements and intensity variation. The intensity variations can perhaps be attributed to the line-of-sight integration effect (Cooper et al 2003). Also the external bundles are brighter than the internal ones, probably from the same lineintegration effect since the external bundles may have a bigger column depth along the line-of-sight (panels c, d).…”

Section: The Multi-thermal Loopmentioning

confidence: 94%

Dynamics of a multi-thermal loop in the solar corona

Nisticò

Anfinogentov

Nakariakov

2014

A&A

Self Cite

View full text Add to dashboard Cite

Context. We present an observation of a long-living multi-thermal coronal loop, visible in different extreme ultra-violet wavebands of SDO/AIA in a quiet-Sun region close to the western solar limb. Aims. Analysis of persistent kink displacements of the loop seen in different bandpasses that correspond to different temperatures of the plasma allows sub-resolution structuring of the loop to be revealed. Methods. A vertically oriented slit is taken at the loop top, and time-distance maps are made from it. Loop displacements in timedistance maps are automatically tracked with the Gaussian fitting technique and fitted with a sinusoidal function that is "guessed". Wavelet transforms are further used in order to quantify the periodicity variation in time of the kink oscillations. Results. The loop strands are found to oscillate with the periods ranging between 3 and 15 min. The oscillations are observed in intermittent regime with temporal changes in the period and amplitude. The oscillations are different at three analysed wavelengths.Conclusions. This finding suggests that the loop-like threads seen at different wavelengths are not co-spatial, hence that the loop consists of several multi-thermal strands. The detected irregularity of the oscillations can be associated with a stochastic driver acting at the footpoints of the loop.

show abstract

Line-of-sight effects on observability of kink and sausage modes in coronal structures with imaging telescopes

Cited by 80 publications

References 22 publications

On oscillations found in an active region with EIS on Hinode

On oscillations found in an active region with EIS on Hinode

Coronal loop seismology using damping of standing kink oscillations by mode coupling

Dynamics of a multi-thermal loop in the solar corona

Contact Info

Product

Resources

About