Evolution of the sun's near-surface asphericities over the activity cycle

Document Type

Article

Publication Date

1-1-2002

Abstract

Solar oscillations provide the most accurate measures of cycle dependent changes in the sun, and the Solar and Heliospheric Observatory/Michelson Doppler Imager (MDI) data are the most precise of all. They give us the opportunity to address the real challenge - connecting the MDI seismic measures to observed characteristics of the dynamic sun. From inversions of the evolving MDI data, one expects to determine the nature of the evolution, through the solar cycle, of the layers just beneath the sun's surface. Such inversions require one to guess the form of the causal perturbation - usually beginning with asking whether it is thermal or magnetic. Matters here are complicated because the inversion kernels for these two are quite similar, which means that we don't have much chance of disentangling them by inversion. However, since the perturbation lies very close to the solar surface, one can use synoptic data as an outer boundary condition to fix the choice. It turns out that magnetic and thermal synoptic signals are also quite similar. Thus, the most precise measure of the surface is required. We argue that the most precise synoptic data come from the Big Bear Solar Observatory (BBSO) Solar Disk Photometer (SDP). A preliminary analysis of these data implies a magnetic origin of the cycle-dependent sub-surface perturbation. However, we still need to do a more careful removal of the facular signal to determine the true thermal signal. Published by Elsevier Science Ltd on behalf of COSPAR.

Identifier

0036601075 (Scopus)

Publication Title

Advances in Space Research

External Full Text Location

https://doi.org/10.1016/S0273-1177(02)00240-5

ISSN

02731177

First Page

1889

Last Page

1898

Issue

12

Volume

29

Grant

ATM-97-14796

Fund Ref

National Science Foundation

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