A search for long-lived velocity fields at the solar poles

A search has been made in the polar regions of the sun for large-scale (50-200 Mm) velocity fields with lifetimes of the order of the solar rotation period (approximately equal to or greater than 30 days). The observations show that any such large-scale, long-lived velocity patterns in the polar regions must have an amplitude less than 5 m/s. Marginally significant detections (at the 2-3 sigma level) were made of two kinds of structures with amplitudes of order 3 m/s. One has a rotation period approximately 38 days (close to the polar rotation period at the sun's surface), and a scale approximately 150 Mm; the other has a period approximately 24 days and a scale approximately 100 Mm. Tentatively, the first structure is interpreted as being of supergranular origin. The second structure is interpreted as the overshooting of the dominant convective mode of the lower solar convection zone - the giant granulation.