Large-scale horizontal flows in the solar photosphere II: Long-term behaviour and magnetic activity response

摘要

Recently, we have developed a method useful for mapping large-scalehorizontal velocity fields in the solar photosphere. The method was developed,tuned and calibrated using the synthetic data. Now, we applied the method tothe series of Michelson Doppler Imager (MDI) dopplergrams covering almost onesolar cycle in order to get the information about the long-term behaviour ofsurface flows. We have found that our method clearly reproduces the widelyaccepted properties of mean flow field components, such as torsionaloscillations and a pattern of meridional circulation. We also performed aperiodic analysis, however due to the data series length and large gaps we didnot detect any significant periods. The relation between the magnetic activityinfluencing the mean zonal motion is studied. We found an evidence that theemergence of compact magnetic regions locally accelerates the rotation ofsupergranular pattern in their vicinity and that the presence of magneticfields generally decelerates the rotation in the equatorial region. Our resultsshow that active regions in the equatorial region emerge exhibiting a constantvelocity (faster by 60 +/- 9 m/s than Carrington rate) suggesting that theyemerge from the base of the surface radial shear at 0.95 R_sun, disconnect fromtheir magnetic roots, and slow down during their evolution.