R. S. Bogart et al.:
Spatially-resolved analysis of the the upper convection-zone
3. Key Results
a. Zonal Flows
- The radial dependence of the anomalous zonal flow (the measured zonal
velocity with respect to the ``standard'' differential rotation rate) through
at least the outer 2% of the Sun (15 Mm) has remained essentially uniform at
each latitude for the last five years. The torsional oscillation amplitude
at each latitude is thus independent of depth and proportional to the
measured surface amplitude.
- The amplitude of the torsional oscillation signal at all depths has
increased regularly, and the latitudes of peak and minimum zonal flow
have moved equatorward, in good agreement with both the surface measurements
and global-mode inversions.
- There is a hint that the asymmetric component of the zonal flow has
reversed, with relatively faster flow in the northern hemisphere during
cycle minimum and in the southern hemisphere during maximum.
b. Meridional Flows
- It appears that the dominant two-cell symmetric meridional circulation
seen at all depths in 1996 and 1997 has given way since 1998 to a somewhat
more complex pattern, with a more extended and intense cell in the southern
hemisphere, and a much weaker cell in the northern hemisphere, possibly
breaking up into a small poleward cell confined to mid- to low-latitudes
and a counter-cell appearing at high latitudes.
- In the years near minimum the mean meridional flow tended to remain
constant or increase slightly with depth through the zone of interest.
The appearance of greater complexity in the flow in recent years in the
northern hemisphere has been accompanied by greater variations in the
radial profile, with substantial poleward flows at greater depths (>
10 Mm) at certain latitudes, and more pronounced reverse flows at depth
at higher latitudes. While the neutral line between the two hemispheric
cells has remained near the equator at the surface, it has migrated to
as much as 20° north latitude below about 10 Mm in the last two years.