On oscillations found in an active region with EIS on Hinode

O’Shea, E.; Doyle, J. G.

doi:10.1051/0004-6361:200810916

Cited by 12 publications

(9 citation statements)

References 14 publications

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“…The power and period distribution of intensity, Doppler velocity and width variations (Figure 9, 10 and 11) reveal that they have a slight tendency to occur preferentially close to the boundaries of the structures where intensity gradients are relatively high. This result confirms earlier observations O'Shea and Doyle, 2009;Rudawy et al, 2010), although they were limited to intensity only. O'Shea and Doyle (2009) reported a variation of wave mode with frequency and location.…”

Section: Discussionsupporting

confidence: 93%

Detection of High-Frequency Oscillations and Damping from Multi-slit Spectroscopic Observations of the Corona

et al. 2015

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During the total solar eclipse of 11 July 2010, multi-slit spectroscopic observations of the solar corona were performed from Easter Island, Chile. To search for "high-frequency waves", observations were taken at a high cadence in the green line at 5303Å due to [Fe xiv] and the red line at 6374Å due to [Fe x].The data are analyzed to study the periodic variations in the intensity, Doppler velocity and line width using wavelet analysis. The data with high spectral and temporal resolution enabled us to study the rapid dynamical changes within coronal structures. We find that at certain locations each parameter shows significant oscillation with periods ranging from 6 -25 s. For the first time, we could detect damping of "high-frequency oscillations" with periods of the order of 10 s. If the observed damped oscillations are due to magnetohydrodynamic (MHD) waves then they can contribute significantly in the heating of the corona. From a statistical study we try to characterize the nature of the observed oscillations while looking at the distribution of power in different line parameters.

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Section: Discussionsupporting

confidence: 93%

Detection of High-Frequency Oscillations and Damping from Multi-slit Spectroscopic Observations of the Corona

et al. 2015

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“…This mechanism can of course also explain the distribution of oscillations in and/or around active regions (Jain & Haber 2002). Recently, oscillations with frequencies between 2 mHz < ν < 8 mHz were found concentrated in bright plage areas (De Wijn & McIntosh 2009;O'Shea & Doyle 2009). Now that we have found a possible link between the solar magnetic features and slow/fast MHD waves, the results from integrated sunlight observations can help us to quantify how much of the solar surface is affected by mode conversion/transmission.…”

Section: Leaking Fast and Slow Mhd Waves To Magnetic Featuresmentioning

confidence: 78%

Acoustic power absorption and enhancement generated by slow and fast MHD waves

Simoniello¹,

Finsterle²,

García³

et al. 2010

A&A

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We used long duration, high quality, unresolved (Sun-as-a star) observations collected by the ground based network BiSON and by the instruments GOLF and VIRGO on board the ESA/NASA SOHO satellite to search for solar-cycle-related changes in mode characteristics in velocity and continuum intensity for the frequency range between 2.5 mHz < ν < 6.8 mHz. Over the ascending phase of solar cycle 23 we found a suppression in the p-mode amplitudes both in the velocity and intensity data between 2.5 mHz < ν < 4.5 mHz with a maximum suppression for frequencies in the range between 2.5 mHz < ν < 3.5 mHz. The size of the amplitude suppression is 13 ± 2 per cent for the velocity and 9 ± 2 per cent for the intensity observations. Over the range of 4.5 mHz < ν < 5.5 mHz the findings hint within the errors to a null change both in the velocity and intensity amplitudes. At still higher frequencies, in the so called High-frequency Interference Peaks (HIPs) between 5.8 mHz < ν < 6.8 mHz, we found an enhancement in the velocity amplitudes with the maximum 36 ± 7 per cent occurring for 6.3 mHz < ν < 6.8 mHz. However, in intensity observations we found a rather smaller enhancement of about 5± 2 per cent in the same interval. There is evidence that the frequency dependence of solar-cycle velocity amplitude changes is consistent with the theory behind the mode conversion of acoustic waves in a non-vertical magnetic field, but there are some problems with the intensity data, which may be due to the height in the solar atmosphere at which the VIRGO data are taken.

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“…Such long‐term background trends are typical of many solar observations, and thus the removal of these trends must be performed strictly in the search for real periodicities in temporal image/spectral data (e.g. Srivastava et al 2008a,b; O'Shea & Doyle 2009, and references therein). There are several ways to remove such long‐term trends (e.g.…”

Section: Wavelet and Periodogram Analysesmentioning

confidence: 99%

“…However, these subarcsec jitters have no effect on the temporal image data in some cases (e.g. O'Shea & Doyle 2009; Srivastava & Dwivedi 2010). We have used the standard cross‐correlation technique to remove the jitter effect from the temporal image data of He ii 256.32 Å, Fe xii 195.12 Å and Fe xv 284.12 Å.…”

Section: Observation and Data Reductionmentioning

confidence: 99%

“…it is not constrained by any specific noise model such as Poisson, Gaussian, etc.). Using this technique, many important results have already been published by analysing approximately evenly sampled data in the solar context (O'Shea et al 2007; Srivastava et al 2008a,b; O'Shea & Doyle 2009; Srivastava & Dwivedi 2010; Srivastava 2010), in the context of active galactic nuclei (Gupta, Srivastava & Wiita 2009), and in the stellar context (Pandey & Srivastava 2009).…”

Section: Wavelet and Periodogram Analysesmentioning

confidence: 99%

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Observations from Hinode/EIS of intensity oscillations above a bright point: signature of the leakage of acoustic oscillations in the inner corona

Srivastava

Dwivedi

2010

Monthly Notices of the Royal Astronomical Society

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We study the intensity oscillations in the upper chromosphere/transition region (TR) and corona, above a bright point (BP) in the solar atmosphere. We analyse the time series of He ii 256 Å, Fe xii 195 Å and Fe xv 284 Å, observed in a 40‐arcsec slot close to the centre of the Sun above the BP by the extreme ultraviolet (EUV) imaging spectrometer (EIS) on board Hinode. Using standard wavelet and periodogram tools, we produce power spectra of intensity oscillations. In the He ii 256.32 Å and Fe xii 195.12 Å EUV light curves, we detect intensity oscillations of the periods ∼ 263 ± 80 s and ∼ 241 ± 60 s, respectively, with a probability >95 per cent in wavelets, which are also consistent with their periodograms. This provides the most likely signature of the propagation of acoustic oscillations around the ∼5.0‐min period from the photosphere to the inner corona. The radiative cooling and thus the finite radiative relaxation time are found to be the most likely mechanisms for the reduced cut‐off frequency environment above the observed BP. This may allow the transfer of ∼5.0‐min acoustic oscillations from the upper chromosphere/TR into the corona. We find that intensity oscillations in He ii 256.32 Å show temporal damping during the total span of the observation. This may be the first most likely observational signature of acoustic wave damping in the upper chromosphere caused by the radiative cooling effect. The intensity oscillations in Fe xii 195.12 Å show an amplification, which may be a most likely signature of the mode‐coupling (two‐wave interaction) and then resonant energy conversion, probably from transverse magnetohydrodynamic (MHD) waves of the double period (e.g. Alfvén waves) to the observed acoustic waves in the lower solar atmosphere where the plasma beta tends to unity. However, we find no evidence of real oscillations around the ∼5.0‐min period with its amplification in the higher corona where the Fe xv 284.16 Å line is formed, which rules out this type of wave activity there. Almost 1.6 per cent of the solar surface is covered with small BPs, probably associated with the small‐scale closed‐loop system, which may be a subset of expanding flux tubes. Hence, the leakage of ∼5.0‐min oscillations above such BPs, which is associated with the highest powers of strong convective motions, and probably resonantly amplified by transverse MHD waves (e.g. Alfvén waves), may be significant for heating the solar atmosphere locally.

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On oscillations found in an active region with EIS on Hinode

Cited by 12 publications

References 14 publications

Detection of High-Frequency Oscillations and Damping from Multi-slit Spectroscopic Observations of the Corona

Detection of High-Frequency Oscillations and Damping from Multi-slit Spectroscopic Observations of the Corona

Acoustic power absorption and enhancement generated by slow and fast MHD waves

Observations from Hinode/EIS of intensity oscillations above a bright point: signature of the leakage of acoustic oscillations in the inner corona

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