  Heat is transported through the outermost 30% of the Sun's interior by
overturning convective motions. These motions are evident at the Sun's surface
in the form of two characteristic cellular structures - granules and
supergranules (~1000 and ~30,000 km across respectively). The existence of much
larger cells has been suggested by both theory and observation for over 45
years. We found evidence for giant cellular flows that persist for months by
tracking the motions of supergranules. As expected from the effects of the
Sun's rotation, the flows in these cells are clockwise around high pressure in
the north, counter-clockwise in the south and transport angular momentum toward
the equator, maintaining the Sun's rapid equatorial rotation.
