Characterizing the Observational Properties of the Sun's High-latitude m=1 Inertial Mode

TL;DR

This study characterizes the Sun's high-latitude m=1 inertial mode using observational data, revealing its power distribution, phase behavior, and relation to solar activity, providing insights into solar interior dynamics.

Contribution

It offers the first detailed analysis of the m=1 inertial mode's properties, including its spatial distribution, phase relations, and response to solar activity, advancing understanding of solar internal dynamics.

Findings

Power is stronger in the northern polar region.

Mode's power anti-correlates with solar activity.

Mode exhibits less differential rotation than surrounding plasma.

Abstract

Low-m inertial modes have been recently discovered in the Sun's high-latitude regions. In this study, we characterize the observational properties of the m = 1 mode by analyzing time-distance subsurface flow maps. Synoptic flow maps, constructed from daily subsurface flow maps using a tracking rate corresponding to the rotation at latitude 65 degrees, are filtered in both the spherical harmonic and Fourier domains to retain only the m = 1 mode and its dominant frequencies. Our analysis reveals a power distribution that is significantly stronger in the northern polar region. The mode's power exhibits an anti-correlation with solar activity, remaining strong and persistent during the solar activity minimum and becoming weaker and more fragmented during the solar maximum. Magnetic flux transported from low to high latitudes influences both the mode's power and lifetime, enhancing its power and shortening its lifetime upon arrival. The phases of the m = 1 mode in the northern and southern polar regions are near-antisymmetric for most of the time with short deviations. We also compute zonal and meridional phase velocities of the mode and find that it exhibits significantly less differential rotation than its surrounding plasma. The meridional phase velocity, comprising both the local plasma's meridional flow and the mode's intrinsic phase motion, is directed poleward below latitude 70 degrees and equatorward above this latitude. These observational findings underscore the need for a deeper understanding of the internal dynamics of the low-m modes, which may offer valuable insights into the structure and dynamics of the solar interior.