On Strengthening of the Solar f-mode Prior to Active Region Emergence Using the Fourier-Hankel Analysis

TL;DR

This study confirms that the solar f-mode power increases 1-3 days before active region emergence using Fourier-Hankel analysis, providing an independent validation of previous ring diagram results and narrowing down physical interpretations.

Contribution

It applies the Fourier-Hankel method to verify prior findings of f-mode power enhancement before active region emergence, offering an independent analysis approach.

Findings

f-mode power increases 1-3 days before AR emergence

No significant absorption or emission of power during enhancement

Absence of directional dependence in wave absorption

Abstract

Recent results of Singh et al. (2016) show that the emergence of an active region (AR) can be seen in a strengthening of the f-mode power up to two days prior of the region's formation. In the original work, ring diagram analysis was used to estimate the power evolution. In this study, we make use of the Fourier-Hankel method, essentially testing the aforementioned results with an independent method. The data is acquired from SDO/HMI, studying the ARs 11158, 11072, 11105, 11130, 11242 and 11768. Investigating the total power as a function of time, we find a similar behavior to the original work, which is an enhancement of f-mode power about one to three days prior to AR emergence. Analysis of the absorption coefficient $\alpha$, yielded by a Fourier-Hankel analysis, shows neither absorption ($\alpha > 0$) nor emission ($\alpha < 0$) of power during the enhancement. Finding no changes of the absorption coefficient (i.e. $\alpha = 0$) is an important result, as it narrows down the possible physical interpretation of the original f-mode power enhancement, showing that no directional dependence (in the sense of inward and outward moving waves) is present.