HELIOSEISMIC IMAGING OF FAST CONVECTIVE FLOWS THROUGHOUT THE NEAR-SURFACE SHEAR LAYER

Using a new implementation of ring-diagram helioseismology, we ascertain the strength and spatial scale of convective flows throughout the near-surface shear layer. Our ring-diagram technique employs highly overlapped analysis regions and an efficient method of three-dimensional inversion to measure convective motions with a resolution that ranges from 3 Mm at the surface to 80 Mm at the base of the layer. We find the rms horizontal flow speed to peak at 427 ms(-1) at the photosphere and fall to a minimum of 124 ms(-1) between 20 and 30 Mm. From the velocity amplitude and the dominant horizontal scales seen at each depth, we infer the level of rotational influence on convection to be low near the surface, but transition to a significant level at the base of the near-surface shear layer with a Rossby number varying between 2.2 to as low as 0.1.