Five-Minute Oscillation Power Within Magnetic Elements in the Solar Atmosphere

Abstract

It has long been known that magnetic plage and sunspots are regions in which the power of acoustic waves is reduced within the photospheric layers. Recent observations now suggest that this suppression of power extends into the low chromosphere and is also present in small magnetic elements far from active regions.In this paper we investigate the observed power supression in plage and magnetic elements, by modelling each as a collection of vertically aligned magnetic fibrils and presuming that the velocity within each fibril is the response to buffeting by incident p modes in the surrounding field-free atmosphere. We restrict our attention to modeling observations made near solar disk center, where the line-ofsight velocity is nearly vertical and hence, only the longitudinal component of the motion within the fibril contributes. Therefore, we only consider the excitation of axisymmetric sausage waves and ignore kink oscillations as their motions are primarily horizontal. We compare the vertical motion within the fibril with the vertical motion of the incident p mode by constructing the ratio of their powers.In agreement with observational measurements we find that the total power is suppressed within strong magnetic elements for frequencies below the acoustic cut-off frequency. We also find that the magnitude of the power deficit increases with the height above the photosphere at which the measurement is made. Further, we argue that the area of the solar disk over which the power suppression extends increases as a function of height.

Time-Dependent Suppression of Oscillatory Power in Evolving Solar Magnetic Fields

“…The observed increase in the spatial extent of the suppression region with height is in agreement with the results of Moretti et al (2007) and Jain et al (2014). Moretti et al (2007) explained their observations based on a mode-conversion model where the power suppression is primarily due to the partial conversion of p-modes into magnetoacoustic waves that go undetected .…”

“…A quantitative comparison of this dependence between different period bands, and across different channels, indicates that the power suppression is steeper for longer periods and at higher atmospheric heights. Using a theoretical model, Jain et al (2014) showed that the power deficit in the suppression region increases with height above the photosphere. They also found that this behaviour manifests with a larger effect when the magnetic field is stronger, which explains the steeper dependence on magnetic field we found at larger heights.…”

“…A similar periodicity is also found in the HMI magnetic field measurements suggesting they are likely to be magnetoacoustic waves. It is possible that they are driven by p-modes originating below the photosphere (see Jain et al 2014;Krishna Prasad et al 2015). In predominantly photospheric channels, the amplitudes are usually small making them difficult to detect in the continuum and G-band channels and perhaps also the reason why they are not easily discernible in the more chromospheric Hα bandpass.…”

“…Using multi-height observations, Moretti et al (2007) observed that the spatial extent of the suppression region increases with height in the solar atmosphere. More recently, through theoretical modelling work, Jain et al (2014) predicted that the power deficit in the suppression region also increases with height. Here, we investigate these aspects using our high spatial-and temporal-resolution observations in four different channels obtained simultaneously with the Dunn Solar Telescope (DST).…”

A study of acoustic halos in active region NOAA 11330 using multi-height SDO observations

“…Two such phenomena; e.g. absorption of p-modes in sunspots around 3 mHz (Jain et al, 2014, and references therein) and enhancement of power around 6 mHz, known as acoustic halos, are signatures of wave interaction with the magnetic field (Schunker & Braun, 2011, and references therein).…”