Abstract


  EFFECTS OF OBSERVATION HEIGHTS AND ATMOSPHERIC WAVE EVOLUTION IN TIME-DISTANCE HELIOSEISMOLOGY OF SUPERGRANULAR FLOWS

  P. Rajaguru, Indian Institute of Astrophysics, rajaguru@iiap.res.in
  H. Antia, TIFR, Mumbai,

We present a comparative study of time-distance helioseismic measurements, made using multi-height observations from the Helioseismic and Magnetic Imager (HMI) (continuum, line-core and Doppler) and the Atmospheric Imaging Assembly (AIA) (1700 and 1600 \AA~) onboard SDO, over several large areas covering small-scale magnetic fields that form the quiet-network. Magnetic field modified wave evolution due to much reduced acoustic cut-off frequencies in inclined field regions is shown to cause height dependent wave phases and hence observation height dependent travel times. We estimate the influence of such effects on the travel-time differences used to measure the supergranular flows. We perform flow inversions under ray-theory approximation and estimate the extent of contamination due to the above effects in the inferred flows. We speculate on the relevance of such effects for the observable dependent center-to-limb effect on helioseismic travel times estimated in meridional flow measurements.