On the rotation rate of the emission solar corona

Whether the differential rotation of the solar photosphere is translated into the corona or not is still an open question. Many studies have shown that small-scale short lived structures exhibit differential rotation associated to one of their footpoints in the photosphere. However, most of the observational studies of the corona (be it in white light or the green coronal line) show an almost rigid rotation at the equatorial rate. Ulysses in-situ measurements of solar wind speed, density and magnetic field strength confirmed this rotation rate even for very high latitudes but showed that near the streamer belt periodicities of longer periods are also present. By using the phase dispersion minimization technique we analyze LASCO-C1 data from April to October 1996 in order to investigate the dependence with latitude and solar distance of the periodicity and recurrence of Fe XIV emission structures. Our results at global scales are consistent with an almost rigid rotation. However, for smaller spatial scales the coexistence of a second periodicity is found, depending on latitude and distance from sun surface. This might correspond to the respective rotation of the photospheric footpoints where the structures are anchored.