Oscillations on the Sun in regions with a vertical magnetic field

Zhukov, V. I.

doi:10.1051/0004-6361:20020279

Cited by 13 publications

(15 citation statements)

References 30 publications

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“…O'Shea et al interpreted their observations in terms of slow magneto-acoustic waves propagating upwards (as confirmed from their time delays) along magnetic field lines. In a recent theoretical paper, Zhukov (2002) calculated the spectrum of eigenmodes of umbral oscillations. It was shown that the 3 min umbral oscillations are the p-modes modified by the magnetic field.…”

Section: Discussionmentioning

confidence: 99%

On the theory of MAG waves and a comparison with sunspot observations from CDS/SoHO

Banerjee

O’Shea

Goossens

et al. 2002

A&A

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Abstract.We examine the influence of non-adiabatic effects on the modes of an isothermal stratified magnetic atmosphere. We present new solutions for magneto-acoustic-gravity (or ) waves in the presence of a radiative heat exchange based on Newton's law of cooling. An analytic expression for the dispersion relation is derived, which allows the effect of a weak magnetic field on the modes to be studied. The insight so gained proves useful in extending the computations to the moderatehigh field case. In the second part we present observations of two sunspots obtained in the  wavelength range with the Coronal Diagnostic Spectrometer () on SoHO. We examine the time series for the line intensities and relative velocities and calculate their power spectra using wavelet transforms. We find oscillations in the chromosphere and transition region above the sunspots in the temperature range log T = 4.6-5.4 K. Most of the spectral power above the umbra is contained in the 5-7 mHz frequency range. When the  slit crosses the sunspot umbra a clear 3 min oscillation is observed. The observed oscillation frequencies are compared with the computed frequencies and the observations are interpreted in terms of the slow magneto-acoustic waves.

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Section: Discussionmentioning

confidence: 99%

On the theory of MAG waves and a comparison with sunspot observations from CDS/SoHO

Banerjee

O’Shea

Goossens

et al. 2002

A&A

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“…Carlsson & Stein (1992) examined the generation of Ca K2V bright points by upwards propagating acoustic shocks in the solar chromosphere, demonstrating that a sinusoidal 180 s period driver was able to produce observed results well. Recent observational work by Marsh & Walsh (2006) has provided evidence of the propagation of oscillatory signals from the transition region into the solar corona in the 3-min period band, and it has been suggested in the past that 3-min oscillations observed in the transition region are connected to the 5-min global p-modes (Bogdan 2000;Zhukov 2002). Leibacher et al (1982) suggest that the observed chromospheric modes are the result of a chromospheric cavity, while Fleck & Schmitz (1991) contend that a cavity is unnecessary to explain the chromospheric oscillations, and that the correct explanation is the resonant excitation of the cut-off frequency at the temperature minimum.…”

Section: Introductionmentioning

confidence: 99%

Leakage of photospheric acoustic waves into non-magnetic solar atmosphere

Erdélyi

Malins

Tóth³

et al. 2007

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Aims. This paper aims to look at the propagation of synthetic photospheric oscillations from a point source into a two-dimensional non-magnetic solar atmosphere. It takes a particular interest in the leakage of 5-min global oscillations into the atmosphere, and aims to complement efforts on the driving of chromospheric dynamics (e.g. spicules and waves) by 5-min oscillations. Methods. A model solar atmosphere is constructed based on realistic temperature and gravitational stratification. The response of this atmosphere to a wide range of adiabatic periodic velocity drivers is numerically investigated in the hydrodynamic approximation. Results. The findings of this modelling are threefold. Firstly, high-frequency waves are shown to propagate from the lower atmosphere across the transition region experiencing relatively low reflection and transmitting energy into the corona. Secondly, it is demonstrated that driving the upper solar photosphere with a harmonic piston driver at around the 5 min period may generate three separate standing modes with similar periods in the chromosphere and transition region. In the cavity formed by the chromosphere and bounded by regions of low cut-off period at the photospheric temperature minimum and the transition region this is caused by reflection, while at either end of this region in the lower chromosphere and transition region the standing modes are caused by resonant excitation. Finally, the transition region becomes a guide for horizontally propagating surface waves for a wide range of driver periods, and in particular at those periods which support chromospheric standing waves. Crucially, these findings are the results of a combination of a chromospheric cavity and resonant excitation in the lower atmosphere and transition region.

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“…As was shown by Zhukov (2002), in sufficiently deep layers (at z → −∞), the system (1) and (2) is divided into two independent subsystems. One of them has the following solutions…”

Section: Initial Conditions In Deep Layers Of a Sunspot Umbramentioning

confidence: 83%

“…Additional difficulties were due to the fact that until now asymptotic solutions of the system of MHD equations have been obtained only for isothermal (Hasan & Christensen-Dalsgaard 1992) and polytropic (with polytropic index µ = 3/2, see Cally & Bogdan 1993;Bogdan & Cally 1997) atmospheres. It was only recently that the asymptotic solutions were found for the atmosphere, in which the Alfvén speed in sufficiently deep layers is considerably smaller than the sound speed (Zhukov 2002). This makes it possible to calculate the spectrum of umbral oscillations for a sufficiently realistic model of the umbra.…”

Section: Introductionmentioning

confidence: 99%

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