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Observations of Global Solar Magnetic and Velocity Fields

Published online by Cambridge University Press:  12 April 2016

J. Todd Hoeksema
J. Todd Hoeksema*
Affiliation:
Center for Space Science & Astrophysics, Stanford, CA 94305, USA

Abstract

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The Sun’s magnetic field varies on time scales of minutes, months, decades, and centuries. These changes drive variations in solar irradiance. Characteristics of the changing magnetic field reveal, at some level, how the solar cycle works. The basic 22-year magnetic cycle and corresponding 11-year activity cycle of the Sun are driven by the emergence of active regions. The frequencies of solar oscillations that probe the convection zone vaxy on the same time scale. While plausible explanations for the statistical properties of solar activity can be made, the details of flux emergence cannot be predicted. Global activity varies on other intermediate time scales as well.

Defining elements of a cycle as those sharing a common bipolar field orientation, the first signs of a cycle can appear at high latitudes up to 5 years before solar minimum and the final elements disappear at the equator several years after the following minimum - a span as long as 18 years. At a particular latitude waves of activity are spaced by 11 years. The torsional oscillation in solar rotation rate has similar characteristics.

The spatial distributions of total flux and large-scale polarity evolve quite differently: the total flux map resembles the butterfly diagram, moving from mid latitudes toward the equator during the cycle, while the net zonal flux has two maxima in each hemisphere that expand away from mid latitudes.

While each solar cycle shares these basic features, fixed by the action of the solar dynamo working within the convection zone, the details of each cycle are determined by the apparently random timing and placement of emerging flux and by the changing convective flow patterns.

Type
Observational Programs for Solar and Stellar Irradiance Variability
Information
International Astronomical Union Colloquium , Volume 143: The Sun as a Variable Star: Solar and Stellar Irradiance Variations , 1994 , pp. 138 - 146
Copyright
Copyright © Kluwer 1994

References

Altrock, R.C. 1988 Variation of solar coronal Fe XIV 5303 emission during solar cycle 21.In Solar and Stellar Coronal Structure and Dynamics (ed. Altrock, R.C.), 414–420.NSO/SP.Google Scholar
Antonucci, E., Hoeksema, J.T. & Scherrer, P.H. 1990 Rotation of the photospheric B fields: a north-south asymmetry. Astrophys. J. 360, 296–304.Google Scholar
Callebaut, D.K. & Makarov, V.I. 1992 Latitude-time distribution of 3 types of B field activity in the global solar cycle. Solar Phys. 141, 381–390.CrossRefGoogle Scholar
Donahue, R.A. & Baliunas, S.L. 1992 Periodogram analysis of 240 years of sunspot records. Solar Phys. 141, 181–198.Google Scholar
Harvey, K.L. 1992 The cyclic behavior of solar activity. In The Solar Cycle (ed. Harvey, K.L.). Astronomical Society of the Pacific Conference Series Vol 27, pp. 335–267.Google Scholar
Komm, R.W., Howard, R.F. & Harvey, J.W. 1993 Torsional oscillation patterns in photo-spheric magnetic features. Solar Phys. 143, 19–40.Google Scholar
Labonte, B.J. & Howard, R. 1982 Torsional waves on the Sun and the activity cycle. Solar Phys. 75, 161–178.CrossRefGoogle Scholar
Makarov, V.I. & Sivaraman, K.R. 1989 New results concerning the global solar cycle. Solar Phys. 123, 367–380.CrossRefGoogle Scholar
Newton, J.W. & Nunn, M.L. 1951 The Sun’s rotation derived from sunspots 1934-1944 and additional results. Monthly Notices of the Royal Astronomical Society 111, 413–421.CrossRefGoogle Scholar
Rabin, D., Devore, C.R., Sheeley, N.R. Jr., Harvey, K.L. & Hoeksema, J.T. 1991 The solar activity cycle. In The Solar Interior and Atmosphere (ed. Cox, A.N., Livingston, W.C. & Matthews, M.S.), 781–843. U. Arizona Press., Tucson, AZ, USA.Google Scholar
Snodgrass, H.B. 1991 A torsional oscillation in the rotation of the solar magnetic field. Astrophys. J. 383, L85–87.CrossRefGoogle Scholar
Stenflo, J.O. & Gudel, M. 1988 Evolution of solar magnetic fields: modal structure. Astron. Astrophys. 191, 137–148.Google Scholar
Zirin, H. 1987 Weak solar fields and their connection to the solar cycle. Solar Phys. 110, 101–107.CrossRefGoogle Scholar