25 research outputs found
Subsurface Meridional Circulation in the Active Belts
Temporal variations of the subsurface meridional flow with the solar cycle
have been reported by several authors. The measurements are typically averaged
over periods of time during which surface magnetic activity existed in the
regions were the velocities are calculated. The present work examines the
possible contamination of these measurements due to the extra velocity fields
associated with active regions plus the uncertainties in the data obtained
where strong magnetic fields are present. We perform a systematic analysis of
more than five years of GONG data and compare meridional flows obtained by
ring-diagram analysis before and after removing the areas of strong magnetic
field. The overall trend of increased amplitude of the meridional flow towards
solar minimum remains after removal of large areas associated with surface
activity. We also find residual circulation toward the active belts that
persist even after the removal of the surface magnetic activity, suggesting the
existence of a global pattern or longitudinally-located organized flows.Comment: 12 pages, 6 figures, Submitted to Solar Physics. Accepted
(08/25/2008
Advances in Global and Local Helioseismology: an Introductory Review
Helioseismology studies the structure and dynamics of the Sun's interior by
observing oscillations on the surface. These studies provide information about
the physical processes that control the evolution and magnetic activity of the
Sun. In recent years, helioseismology has made substantial progress towards the
understanding of the physics of solar oscillations and the physical processes
inside the Sun, thanks to observational, theoretical and modeling efforts. In
addition to the global seismology of the Sun based on measurements of global
oscillation modes, a new field of local helioseismology, which studies
oscillation travel times and local frequency shifts, has been developed. It is
capable of providing 3D images of the subsurface structures and flows. The
basic principles, recent advances and perspectives of global and local
helioseismology are reviewed in this article.Comment: 86 pages, 46 figures; "Pulsation of the Sun and Stars", Lecture Notes
in Physics, Vol. 832, Rozelot, Jean-Pierre; Neiner, Coralie (Eds.), 201
Perspectives in Global Helioseismology, and the Road Ahead
We review the impact of global helioseismology on key questions concerning
the internal structure and dynamics of the Sun, and consider the exciting
challenges the field faces as it enters a fourth decade of science
exploitation. We do so with an eye on the past, looking at the perspectives
global helioseismology offered in its earlier phases, in particular the
mid-to-late 1970s and the 1980s. We look at how modern, higher-quality, longer
datasets coupled with new developments in analysis, have altered, refined, and
changed some of those perspectives, and opened others that were not previously
available for study. We finish by discussing outstanding challenges and
questions for the field.Comment: Invited review; to appear in Solar Physics (24 pages, 6 figures