Paper detail

Multi-height Scattering Phase Shifts From Sunspots And Phase Differences Between Photospheric Heights With SDO/HMI and AIA Data

Following Couvidat (2013), we analyze data from the Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) instruments onboard the Solar Dynamics Observatory: Doppler velocity and continuum intensity at 6173 A as well as intensity maps at 1600 A and 1700 A. Datasets of 14 active regions and four quiet-Sun regions are studied at four heights in the solar photosphere. An Hankel-Fourier analysis is performed around these regions of interest. Outgoing-ingoing scattering phase shifts at a given atmospheric height are computed, as well as ingoing-ingoing and outgoing-outgoing phase differences between two atmospheric heights. The outgoing-ingoing phase shifts produced by sunspots show little dependence on measurement height, unlike the acoustic power reduction measured in Couvidat (2013). Phenomena happening above continuum level, like acoustic glories, appear not to have a significant effect on the phases. However there is a strong dependence on sunspot size, line-of-sight magnetic flux, and intensity contrast. As previously suggested by other groups, the region of wave scattering appears both horizontally smaller and vertically less extended than the region of acoustic power suppression, and occurs closer to the surface. Results presented here should help refine theoretical models of acoustic wave scattering by magnetic fields. Ingoing-ingoing phase differences between two measurement heights are also computed and show a complex pattern highly dependent on atmospheric height. In particular, a significant sensitivity of AIA signals to lower chromospheric layers is shown. Finally, ingoing-ingoing minus outgoing-outgoing phase differences between various measurement heights are discussed.