10 To 40 nHz Oscillations in Spherical Harmonic Representations of Sunspot Patterns Yield a Square-Root Dispersion Relationship With Respect to Harmonic Order.

Details 10 To 40 nHz Oscillations in Spherical Harmonic Representations of Sunspot Patterns Yield a Square-Root Dispersion Relationship With Respect to Harmonic Order. 10 To 40 nHz Oscillations in Spherical Harmonic Representations of Sunspot Patterns Yield a Square-Root Dispersion Relationship With Respect to Harmonic Order.

May 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsp43b..06j&link_type=abstract

American Geophysical Union, Spring Meeting 2005, abstract #SP43B-06

Physics

7522 Helioseismology, 7536 Solar Activity Cycle (2162), 7537 Solar And Stellar Variability

Scientific paper

The temporal changes in the 2-dimensional patterns of sunspots groups, spanning 1650 Carrington Rotations (CRs), were previously analyzed using surface spherical harmonics (SSHs). (Juckett, 2003, A&A, 399, 731.) The focus of that paper was to examine the common trends in the oscillations of both the amplitudes and spatial phases of sectoral combinations of SSHs. The amplitude analysis revealed strong evidence for the first and second harmonics of the 11-yr cycle across all SSHs. A further analysis of SSH amplitude variations is continued here. The Principle Components (PCs) located just after the second harmonic were extracted from individual sectoral SSHs. An apparent dispersion relationship appeared between the major frequencies of these PCs and SSH order, which has a near square-root dependence. The dispersion spans frequencies of approximately 10 to 40 nHz over the order range m=2 to m=18, indicating large-scale oscillations with very long periods (0.8 to 3 yr). Abrupt changes in the spatial phases of the SSHs, which are a hallmark of standing waves, also show a compatible dispersion relationship. In general, the square-root dependence would suggest g-mode oscillations, but the periods are far longer than predicted for such oscillations. While the source of these oscillations cannot be determined by this analysis, it suggests such mechanisms as the splitting of g-mode oscillations by differential rotation and the beating of the resultant closely spaced oscillations, or perhaps very long period internal waves, with an f-mode character, near the tachocline. In the latter case, the frequency range of the dispersion would require a reduced gravity of ~ 10-4 for such internal waves. This seems highly unlikely unless the local magnetic pressure is sufficient to generate such a region. These mechanisms as well as issues of data quality will be discussed.

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