Nitin Yadav

NameNitin Yadav
AffiliationKU Leuven, Belgium
TitleSlow Magneto-acoustic Wave Propagation in Three-Dimensional Simulations of a Unipolar Solar Plage
AuthorsNitin Yadav, R H Cameron, and S K Solanki
AbstractWe investigate the properties of slow magneto-acoustic waves that are naturally excited due to turbulent convection and investigate their role in the energy balance of a plage region using three dimensional (3D) radiation-MHD simulations. To study slow magneto-acoustic waves traveling along the magnetic field lines, we track 25 magnetic field lines both in space and time inside a strong magnetic element. We calculate velocity component parallel to the background field and compute the temporal power spectra at various heights above the mean solar surface. Additionally, horizontally averaged (over the whole domain) power spectra for both longitudinal (parallel to the background magnetic field) and vertical (i.e. the component perpendicular to the surface) components of velocity are calculated using time-series at fixed locations. We also degrade our simulation data to compare our results with observations. The power spectra of longitudinal component of velocity, averaged over 25 field lines in the core of a kG magnetic flux concentration, reveal that the dominant period of oscillations shifts from ∼ 6.5 minutes in the photosphere to ∼ 4 minutes in the chromosphere. This behaviour is consistent with earlier studies restricted to vertically propagating waves. At the same time, the velocity power spectra, averaged horizontally over the whole domain, show that low frequency waves (∼ 6.5 minute period) may reach well into the chromosphere possibly along the inclined magnetic field lines at the edges of selected magnetic patch. In addition, the power spectra at high frequencies follow a power law with an exponent close to -5/3, suggestive of turbulent excitation. The horizontally averaged power spectra of vertical component of velocity at various effective resolutions show that the observed acoustic wave energy fluxes are underestimated, by a factor of three even if determined from observations carried out at a high spatial resolution of 100 km. Since the waves propagate along the non-vertical field lines, measuring the velocity component along the line-of-sight, rather than along the field contributes significantly to this underestimate. Moreover, this underestimation of energy flux indirectly indicates the importance of high-frequency waves that are shown to have a smaller spatial coherence and are thus more strongly influenced by spatial averaging effect compared to low-frequency waves. Our results show that, in contrast to claims made in the literature, longitudinal waves within magnetic elements carry sufficient energy to heat the chromosphere, although only just.