Temporal Filters for Isolating Steady Photospheric Flows
Abstract
A variety of temporal filters are tested on artificial data with 60 and 75 s sampling intervals to determine their accuracy in separating the nearlysteady photospheric flows from the pmode oscillations in Doppler velocity data. Longer temporal averages are better at reducing the residual signal due to pmodes but they introduce additional errors from the rotation of the supergranule pattern across the solar disk. Unweighted filters (boxcar averages) leave residual r.m.s. errors of about 6 m s^{1} from the pmodes after 60 min of averaging. Weighted filters, with nearly Gaussian shapes, leave similar residual errors after only 20 min of averaging and introduce smaller errors from the rotation of the supergranule pattern. The best filters found are weighted filters that use data separated by 150 or 120 s so that the pmodes are sampled at opposite phases. These filters achieve an optimum error level after about 20 min, with the r.m.s. errors due to the pmode oscillations and the rotation of the supergranules both at a level of only 1.5 m s^{1}.
 Publication:

Solar Physics
 Pub Date:
 March 1988
 DOI:
 10.1007/BF00148567
 Bibcode:
 1988SoPh..117....1H
 Keywords:

 Photosphere;
 Solar Oscillations;
 Vibration Mode;
 Doppler Effect;
 Error Analysis;
 Fourier Transformation;
 Solar Velocity;
 Time Series Analysis;
 Solar Physics