Comparing local frequency shifts measured through ring-diagram analysis with global frequency shifts

Details Comparing local frequency shifts measured through ring-diagram analysis with global frequency shifts Comparing local frequency shifts measured through ring-diagram analysis with global frequency shifts

Jan 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001esasp.464..143h&link_type=abstract

In: Proceedings of the SOHO 10/GONG 2000 Workshop: Helio- and asteroseismology at the dawn of the millennium, 2-6 October 2000,

Physics

Optics

6

Sun: Oscillations

Scientific paper

Using ring-diagram mode fitting of a subset of the MDI Dynamics Program data called the dense-pack data set (Haber et al. 2000), we measure the frequencies of high-degree p modes and f modes as a function of position on the solar disk and of time. Daily maps of the resulting frequencies reveal that high-degree mode frequencies are spatially and temporally variable and are composed of the sum of two components. One component is stationary and is produced primarily by imperfections in the MDI optics, while the other component is spatially intermittent, rotates with the solar surface, and is associated with the presence of active regions. The frequency shifts within active regions can exceed 60 μHz for some wavelengths and mode orders. We remove the instrumentally dependent portion of the signal and average the resulting frequency shifts over the solar disk and over time producing a global average. The frequency and wavenumber dependence of these average frequency shifts indicates that the physical phenomena inducing the shifts is largely confined to the surface layers of the sun, although there is evidence that a small contribution from deeper layers exists. The average frequency shifts strongly resemble the solar cycle variations that are observed in the frequencies of global p-mode oscillations of low harmonic degree.

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