B{sub}0-ANGLE EFFECT ON ZONAL AND MERIDIONAL FLOW DETERMINATIONS FROM 3 YEARS RING DIAGRAM ANALYSIS OF GONG++ DATA

摘要

We study zonal and meridional components of horizontal solar subsurface flows during the years 2001-2004 which covers the declining phase of solar cycle 23. We measure the horizontal flows from the near surface layers to 16 Mm in depth by analyzing 44 consecutive Carrington rotations of Global Oscillation Network Group (GONG) Doppler images with a ring-diagram analysis technique. The meridional flow shows an annual variation related to the B{sub}0-angle variation, while the zonal flow is less affected by this 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.