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Sakurai, Takashi; Ichimoto, Kiyoshi; Raju, K. P.; Singh, Jagdev

doi:10.1023/a:1021297313448

Cited by 68 publications

(50 citation statements)

References 24 publications

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“…The characteristic periods are several hundred seconds (180-600 s). Similar periodicities have recently been observed in the coronal green line (Sakurai et al 2002). According to De Moortel et al (2002a-c), shorter period disturbances are usually observed over the sunspots, while longer period disturbances normally propagate along loops which are not associated with sunspots.…”

Section: Introductionsupporting

confidence: 78%

Propagating EUV disturbances in the Solar corona: Two-wavelength observations

King

Nakariakov

DeLuca

et al. 2003

A&A

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Abstract. Quasi-periodic EUV disturbances simultaneously observed in 171 Å and 195 Å TRACE bandpasses propagating outwardly in a fan-like magnetic structure of a coronal active region are analysed. Time series of disturbances observed in the different bandpasses have a relatively high correlation coefficient (up to about 0.7). The correlation has a tendency to decrease with distance along the structure: this is consistent with an interpretation of the disturbances in terms of parallelpropagating slow magnetoacoustic waves. The wavelet analysis does not show a significant difference between waves observed in different bandpasses. Periodic patterns of two distinct periods: 2-3 min and 5-8 min are detected in both bandpasses, existing simultaneously and at the same distance along the loop, suggesting the nonlinear generation of the second harmonics.

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Section: Introductionsupporting

confidence: 78%

Propagating EUV disturbances in the Solar corona: Two-wavelength observations

King

Nakariakov

DeLuca

et al. 2003

A&A

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“…For S xv, the intensity peak occurs 1.54 minutes after the Doppler shift peak. This corresponds to a delay of 1/4 of the period, strongly suggesting that the oscillations observed in this flare are due to slow standing-mode MHD waves (Sakurai et al 2002).…”

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confidence: 76%

Characteristics of Solar Flare Doppler‐Shift Oscillations Observed with the Bragg Crystal Spectrometer onYohkoh

Mariska

2006

ApJ

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, and inferred displacements of 1070 AE 1710 km, where the listed errors are the standard deviations of the sample means. For some of the flares, intensity fluctuations are also observed. These lag the Dopplershift oscillations by 1/4 period, strongly suggesting that the oscillations are standing slow-mode waves. The relationship between the oscillation period and the decay time is consistent with conductive damping of the oscillations.

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“…Whether a slow-mode wave is a propagating or standing wave can be inferred from the phase relationship between velocity and intensity: propagating waves give an in-phase variation, whereas standing waves give a 1/4-period phase difference (Sakurai et al 2002). Thus, based on an in-phase relationship with the line intensity, Sakurai et al (2002) Thus, these observations indicate the presence of slow standing waves in hot coronal loops.…”

Section: Oscillations In the Slow Standing Modementioning

confidence: 99%

Hot coronal loop oscillations observed with SUMER: Examples and statistics

Wang

Solanki

Curdt

et al. 2003

A&A

195

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Abstract.We give an extensive overview of Doppler shift oscillations in hot active region loops obtained with SUMER. The oscillations have been detected in loops sampled 50−100 arcsec off the limb of the Sun in ultraviolet lines, mainly Fe  and Fe , with formation temperature greater than 6 MK. The spectra were recorded along a 300 arcsec slit placed at a fixed position in the corona above the active regions. Oscillations are usually seen along an extended section of the slit and often appear to be from several different portions of the loops (or from different loops). Different portions are sometimes in phase, sometimes out of phase and sometimes show phase shifts along the slit. We measure physical parameters of 54 Doppler shift oscillations in 27 flare-like events and give geometric parameters of the associated hot loops when soft X-ray (SXR) images are available. The oscillations have periods in the range 7−31 min, with decay times 5.7−36.8 min, and show an initial large Doppler shift pulse with peak velocities up to 200 km s −1 . The oscillation periods are on average a factor of three longer than the TRACE transverse loop oscillations. The damping times and velocity amplitude are roughly the same, but the derived displacement amplitude is four or five times larger than the transverse oscillation amplitude measured in TRACE images. Unlike TRACE oscillations, only a small fraction of them are triggered by large flares, and they often recur 2−3 times within a couple of hours. All recurring events show initial shifts of the same sign. These data provide the following evidence to support the conclusion that these oscillations are slow magnetoacoustic standing waves in hot loops: (1) the phase speeds derived from observed periods and loop lengths roughly agree with the sound speed; (2) the intensity fluctuation lags the Doppler shifts by 1/4 period; (3) The scaling of the dissipation time of slow waves with period agrees with the observed scaling for 49 cases. They seem to be triggered by micro-or subflares near a footpoint, as revealed in one example with SXR image observations. However other mechanisms cannot as yet be ruled out. Some oscillations showed phase propagation along the slit in one or both directions with apparent speeds in the range of 8−102 km s −1 , together with distinctly different intensity and line width distributions along the slit. These features can be explained by the excitation of the oscillation at a footpoint of an inhomogeneous coronal loop, e.g. a loop with fine structure.

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Untitled

Cited by 68 publications

References 24 publications

Propagating EUV disturbances in the Solar corona: Two-wavelength observations

Propagating EUV disturbances in the Solar corona: Two-wavelength observations

Characteristics of Solar Flare Doppler‐Shift Oscillations Observed with the Bragg Crystal Spectrometer onYohkoh

Hot coronal loop oscillations observed with SUMER: Examples and statistics

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