Preliminary Results of Solar Latitudinal Differential Rotational Pattern Deduced From Traces of Supergranulations Observed by Taiwan Oscillation Network

Solar latitudinal differential rotation, which can generate toroidal magnetic field from a poloidal magnetic field, plays an important role on solar dynamo and formation of solar cycle. Solar differential rotation law obtained from sunspots motion is only applicable to the middle and lower latitude and has a poor latitudinal resolution during solar minimum. Supergranulations, or chromosphere networks, are excellent targets for studying solar differential rotation in all latitudes and during different phases of solar cycle. Differential rotation of supergranulations has been studied using MDI Dopplergrams. The one-minute broadband K-line images obtained from Taiwan Oscillation Network (TON) provide another kind of data set to study differential rotation of supergranulations up to very high latitude. Differential rotation rate of supergranulations during raising phase of solar cycle 23 are studied. Our preliminary results indicate that for latitude less than 60 degrees, rotation rate of super-granulations decreases with increasing latitude, which can be approximated by a quadratic function of sin²(latitude). For latitude greater than 60 degrees, one or two reversed differential rotational patterns are found. Our preliminary results are similar to the differential rotational pattern observed below the photosphere as obtained by helioseismology analysis of MDI data. The cause of the observed solar differential rotational pattern will be discussed.