Rotation and Flows from Global Fitting (2003)
Inversions of global p modes with degree up to 150 from GONG allow us
to probe the changing dynamics of the solar convection zone, with
observations stretching from 1995, before the last solar minimum, to just
after solar maximum.
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Mean Rotation Profile |
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The figure above shows the mean rotation profile derived from 66
overlapping 108-day periods of GONG data starting in May 1995 and
continuing through December 2001. The isorotation contours are spaced
at 5nHz. The contours in the bulk of the convection zone, below the
subsurface shear layer and above the tachocline, maintain almost the
same angle to the vertical over a wide range of latitudes.
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The figure above shows the angle between the rotation contours and the rotation axis for the observations (red) and for a notional profile (green) with contours along radial lines. Notice that the observed contours are always steeper than the radial picture would suggest. The latitudes were measured at the middle of the convection zone, and the angles were measured over the interval 0.8 < r/RSUN < 0.95.
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Zonal Flows
By subtracting the temporal mean rotation profile from the individual
inversions, we reveal the pattern of flows that migrates from
mid-latitudes to the equator, as well as the larger-amplitude variations
at higher latitudes. In the plots below, we show the observed rotation
residuals (top) and the pattern obtained by fitting a sinusoidal variation
of period 11y at each location. |
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When the resolution and noise of the data are taken into account, the data suggest that the flows seen at the surface persist through at least half the depth of the convection zone, but with a significant phase variation with depth; the variation near the base of the convection zone appears to lead that near the surface by as much as two years, but because of the noise levels this inference needs to be treated with caution.
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