North – South Asymmetry of Zonal and Meridional Flows Determined From Ring Diagram Analysis of Gong ++ Data |
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Authors: | A Zaatri R Komm I González Hernández R Howe T Corbard |
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Institution: | 1. Centre de Recherche en Astronomie Astrophysique et Geophysique, B.P. 63 Bouzaréah, Algiers, 16340, Algeria 2. National Solar Observatory, 950 N. Cherry Ave., Tucson, AZ, 85719, U.S.A. 3. Observatoire de la C?te d'Azur, F-06304, Nice Cedex 4, France
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Abstract: | We study the North–South asymmetry of zonal and meridional components of horizontal, solar subsurface flows during the years
2001–2004, which cover the declining phase of solar cycle 23. We measure the horizontal flows from the near-surface layers
to 16 Mm depth by analyzing 44 consecutive Carrington rotations of Global Oscillation Network Group (GONG) Doppler images
with a ring-diagram analysis technique. The meridional flow and the errors of both flow components show an annual variation
related to the B
0-angle variation, while the zonal flow is less affected by the B
0-angle variation. After correcting for this effect, the meridional flow is mainly poleward but it shows a counter cell close
to the surface at high latitudes in both hemispheres. During the declining phase of the solar cycle, the meridional flow mainly
increases with time at latitudes poleward of about 20˚, while it mainly decreases at more equatorward latitudes. The temporal variation of the zonal flow in both hemispheres is
significantly correlated at latitudes less than about 20˚. The zonal flow is larger in the southern hemisphere than the northern one, and this North–South asymmetry increases with
depth. Details of the North–South asymmetry of zonal and meridional flow reflect the North–South asymmetry of the magnetic
flux. The North–South asymmetries of the flows show hints of a variation with the solar cycle. |
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