Abstract
Using data from the Helioseismic Magnetic Imager, we report on the amplitudes and phase relations of oscillations in quiet-Sun, plage, umbra and the polarity inversion line (PIL) of an active region NOAA#11158. We employ Fourier, wavelet and cross-correlation spectra analysis. Waves with 5 min periods are observed in umbra, PIL and plage with common phase values of ϕ(v, I) = π/2, ϕ(v, Blos) = −(π/2). In addition, ϕ(I, Blos) = π in plage are observed. These phase values are consistent with slow standing or fast standing surface sausage wave modes. The line width variations, and their phase relations with intensity and magnetic oscillations, show different values within the plage and PIL regions, which may offer a way to further differentiate wave mode mechanics. Significant Doppler velocity oscillations are present along the PIL, meaning that plasma motion is perpendicular to the magnetic field lines, a signature of Alvènic waves. A time–distance diagram along a section of the PIL shows Eastward propagating Doppler oscillations converting into magnetic oscillations; the propagation speeds range between 2 and 6 km s−1. Lastly, a 3 min wave is observed in select regions of the umbra in the magnetogram data.This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.
Highlights
The Sun is a seething mass of plasma with a great variety of magnetic fields and electric currents being dynamically generated and distributed throughout its layers
Using data from the Helioseismic Magnetic Imager, we report on the amplitudes and phase relations of oscillations in quiet-Sun, plage, umbra and the polarity inversion line (PIL) of an active region NOAA#11158
Alfvén waves [1] are the least impeded of the MHD waves since they are not reflected by pressure gradients and may reach the corona before dissipating [2] and may play a role in the acceleration of the solar wind
Summary
The Sun is a seething mass of plasma with a great variety of magnetic fields and electric currents being dynamically generated and distributed throughout its layers. The work by [28,31], who studied different types of solar structures (large and small sunspots, a pore and faculae region) at photospheric and chromospheric heights, showed that ‘while the atmospheric cut-off frequency and the propagation properties of different oscillating modes depend on the magnetic feature, in all the cases, the power that reaches the high chromosphere above the atmospheric cut-off comes directly from the photosphere by means of linear vertical wave propagation rather than from nonlinear interaction of modes.’. The spatial distribution of power from the Fourier transform for the 512 × 512 region, averaged over select frequency ranges, is shown in figure 4, with context images of the line-of-sight data shown on the bottom row
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