caa a22 4500 445347392 CHVBK 20180317142833.0 cr unu---uuuuu 170323e20110701xx s 000 0 eng 10.1007/s11207-011-9783-9 doi (NATIONALLICENCE)springer-10.1007/s11207-011-9783-9 On the Formation Height of the SDO/HMI Fe 6173 Å Doppler Signal [Elektronische Daten] [B. Fleck, S. Couvidat, T. Straus] The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) is designed to study oscillations and the magnetic field in the solar photosphere. It observes the full solar disk in the Fe i absorption line at 6173Å. We use the output of a high-resolution, 3D, time-dependent, radiation-hydrodynamic simulation based on the CO 5 BOLD code to calculate profiles F(λ,x,y,t) for the Fe i 6173Å line. The emerging profiles F(λ,x,y,t) are multiplied by a representative set of HMI filter-transmission profiles R i (λ, 1≤i≤6) and filtergrams I i (x,y,t; 1≤i≤6) are constructed for six wavelengths. Doppler velocities V HMI(x,y,t) are determined from these filtergrams using a simplified version of the HMI pipeline. The Doppler velocities are correlated with the original velocities in the simulated atmosphere. The cross-correlation peaks near 100km, suggesting that the HMI Doppler velocity signal is formed rather low in the solar atmosphere. The same analysis is performed for the SOHO/MDI Ni i line at 6768Å. The MDI Doppler signal is formed slightly higher at around 125km. Taking into account the limited spatial resolution of the instruments, the apparent formation height of both the HMI and MDI Doppler signal increases by 40 to 50km. We also study how uncertainties in the HMI filter-transmission profiles affect the calculated velocities. Springer Science+Business Media B.V., 2011 Line formation nationallicence Oscillations nationallicence Photosphere nationallicence Sun nationallicence Fleck B. ESA Science Operations Department, c/o NASA/GSFC, Greenbelt, MD, USA aut Couvidat S. W.W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA aut Straus T. INAF Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131, Napoli, Italy aut Solar Physics Springer Netherlands 271/1-2(2011-07-01), 27-40 0038-0938 271:1-2<27 2011 271 11207 https://doi.org/10.1007/s11207-011-9783-9 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s11207-011-9783-9 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Fleck B. ESA Science Operations Department, c/o NASA/GSFC, Greenbelt, MD, USA aut NATIONALLICENCE 700 1- Couvidat S. W.W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA aut NATIONALLICENCE 700 1- Straus T. INAF Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131, Napoli, Italy aut NATIONALLICENCE 773 0- Solar Physics Springer Netherlands 271/1-2(2011-07-01), 27-40 0038-0938 271:1-2<27 2011 271 11207 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer