Quasi-Periodic Oscillations of Microwave Emission in Solar Active Regions

Gelfreikh, G. B.; Nagovitsyn, Yu. A.; Nagovitsyna, E. Yu.

doi:10.1093/pasj/58.1.29

Cited by 62 publications

(25 citation statements)

References 14 publications

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“…In microwave emission above sunspots, oscillations of tens and hundreds of minutes have been detected (Gelfreikh et al 2006;Chorley et al 2010) with the Nobeyama Radioheliograph (NoRH, Nakajima et al 1994). In particular, Chorley et al (2010) indicated the presence of two periodicities in each analysed sunspot.…”

Section: Introductionmentioning

confidence: 99%

Period persistence of long period oscillations in sunspots

Chorley

Foullon

Hnat

et al. 2011

A&A

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Long period oscillations in the microwave radiation intensity generated over the sunspot of NOAA AR 10330 are studied with the Nobeyama Radioheliograph as the sunspot passes over the solar disk, over the course of 9 days (06−15 April 2003). Periodogram, Fourier and global wavelet analyses reveal the presence of a significant oscillatory component in the range P ≈ 50−120 min over the course of the observations. The spectral amplitudes of five significant Fourier components in the range P = 50−150 min are also seen to be stable over the observations, when the data are not affected by changes in magnetic configuration in the region. The ground-based nature of the instrument naturally introduces long data gaps in such long duration observations and the presence of the gaps does not allow any conclusion as to the stability of the phases of the oscillations. As a model to explain the persistence of the dominant long periods, a simple oscillator with a nonlinear driving term is proposed. The spectral difference between distinct peaks within, e.g. the 3 min spectral band, is expected to be able to resonate with the long period one hour oscillations.

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Section: Introductionmentioning

confidence: 99%

Period persistence of long period oscillations in sunspots

Chorley

Foullon

Hnat

et al. 2011

A&A

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“…For example, 30-60 min oscillations have been detected in the intensity difference of two solar radio signals recorded at two close frequencies, 9.67 GHz and 9.87 GHz (Kobrin & Korshunov 1972). Oscillation periods of tens and hundreds of minutes have also been seen as modulation of the microwave emission (Gelfreikh et al 2006). Recently, oscillations of the line-of-sight velocity with periods from 60 to 80 min have been detected in sunspots (Efremov et al 2009) in the Doppler shift of lines in the sunspot spectrum formed at different heights.…”

Section: Introductionmentioning

confidence: 99%

Long period oscillations in sunspots

Chorley¹,

Hnat²,

Nakariakov³

et al. 2010

A&A

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Long period oscillations of the gyroresonant emission from sunspot atmospheres are studied. Time series data generated from the sequences of images obtained by the Nobeyama Radioheliograph operating at a frequency of 17 GHz for three sunspots have been analysed and are found to contain significant periods in the range of several tens of minutes. Wavelet analysis shows that these periods are persistent throughout the observation periods. The presence of the oscillations is confirmed by several methods (periodogram, wavelets, Fisher randomisation and empirical mode decomposition). Spatial analysis using the techniques of period, power, correlation and time lag mapping reveals regions of enhanced oscillatory power in the umbral regions. Also seen are two regions of coherent oscillation of about 25 pixels in size, that oscillate in anti-phase with each other. Possible interpretation of the observed periodicities is discussed, in terms of the shallow sunspot model and the leakage of the solar g-modes.

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“…The quasi-periodic oscillations are registered practically in all wavelength ranges and in all structures of the solar atmosphere (Bogdan 2000, Fludra 2001, Gelfreikh, Nagovitsyn & Nagovitsyna 2006. Oscillations have periods from seconds to hours or even days.…”

Section: Introductionmentioning

confidence: 93%

A comparison of parameters of 3-minute and 5-minute oscillations in sunspots from synchronous microwave and optical observations

Abramov-Maximov¹,

Gelfreikh²,

Кобанов

et al. 2008

Proc. IAU

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Abstract. The observations of 3 and 5 minute oscillations in sunspots present information on propagation of MHD waves in the magnetic tubes of sunspots. We present a comparison of wavelet spectra of radio flux oscillations at λ = 1.76 cm and oscillations of longitudinal component of the velocity at the chromosphere in sunspot umbra and penumbra in AR 10661 (2004, Aug 18). The radio maps of the Sun obtained with the Nobeyama Radioheliograph were used. The spatial resolution of the radio data was about 10-15 arcsec, and 10 sec cadence was used. On the radio maps sunspot-associated sources were identified and time profiles of their maximum brightness temperatures for each radio source were calculated. Radio data consists of information of oscillations of plasma parameters (in the regions with magnetic field B = 2000 G) at the level of the chromosphere-corona transition region. The optical observations were carried out at Sayan observatory. These data included information on longitude component of the magnetic field at the photosphere (line Fe I 6569Å) and longitudinal component of the velocity at the chromosphere (line Hα was used). Comparing the wavelet diagrams covering the same periods of observations at radio and optics showed that some wave trains of time profiles are very similar in both kinds of observations (similar oscillation frequencies and their drifts, variations of amplitudes), however, some significant differences were also registered. The best similarity in optical and radio oscillations was found when the active region (AR) was near the center of the solar disk. The phase shifts between the two kinds of observations reflecting the propagation of MHD waves were also analyzed.

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Quasi-Periodic Oscillations of Microwave Emission in Solar Active Regions

Cited by 62 publications

References 14 publications

Period persistence of long period oscillations in sunspots

Period persistence of long period oscillations in sunspots

Long period oscillations in sunspots

A comparison of parameters of 3-minute and 5-minute oscillations in sunspots from synchronous microwave and optical observations

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