Interpreting the Helioseismic and Magnetic Imager (HMI) Multi-Height Velocity Measurements

Kaori Nagashima, Björn Löptien, Laurent Gizon, Aaron C. Birch, Robert Cameron, Sebastien Couvidat, Sanja Danilovic, Bernhard Fleck, Robert Stein

    Research output: Contribution to journalArticle

    Abstract

    The Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) filtergrams, taken at six wavelengths around the Fe i 6173.3 Å line, contain information about the line-of-sight velocity over a range of heights in the solar atmosphere. Multi-height velocity inferences from these observations can be exploited to study wave motions and energy transport in the atmosphere. Using realistic convection-simulation datasets provided by the STAGGER and MURaM codes, we generate synthetic filtergrams and explore several methods for estimating Dopplergrams. We investigate at which height each synthetic Dopplergram correlates most strongly with the vertical velocity in the model atmospheres. On the basis of the investigation, we propose two Dopplergrams other than the standard HMI-algorithm Dopplergram produced from HMI filtergrams: a line-center Dopplergram and an average-wing Dopplergram. These two Dopplergrams correlate most strongly with vertical velocities at the heights of 30 - 40 km above (line center) and 30 - 40 km below (average wing) the effective height of the HMI-algorithm Dopplergram. Therefore, we can obtain velocity information from two layers separated by about a half of a scale height in the atmosphere, at best. The phase shifts between these multi-height Dopplergrams from observational data as well as those from the simulated data are also consistent with the height-difference estimates in the frequency range above the photospheric acoustic-cutoff frequency.

    Original languageEnglish (US)
    Pages (from-to)3457-3481
    Number of pages25
    JournalSolar Physics
    Volume289
    Issue number9
    DOIs
    StatePublished - Jan 1 2014

    Fingerprint

    velocity measurement
    filtergrams
    atmosphere
    atmospheres
    wings
    helioseismology
    scale height
    solar atmosphere
    inference
    line of sight
    observatories
    convection
    estimating
    phase shift
    cut-off
    frequency ranges
    acoustics
    observatory
    wavelength
    estimates

    Keywords

    • Helioseismology, observations
    • Oscillations, solar
    • Velocity fields, photosphere

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

    Cite this

    Nagashima, K., Löptien, B., Gizon, L., Birch, A. C., Cameron, R., Couvidat, S., ... Stein, R. (2014). Interpreting the Helioseismic and Magnetic Imager (HMI) Multi-Height Velocity Measurements. Solar Physics, 289(9), 3457-3481. https://doi.org/10.1007/s11207-014-0543-5

    Interpreting the Helioseismic and Magnetic Imager (HMI) Multi-Height Velocity Measurements. / Nagashima, Kaori; Löptien, Björn; Gizon, Laurent; Birch, Aaron C.; Cameron, Robert; Couvidat, Sebastien; Danilovic, Sanja; Fleck, Bernhard; Stein, Robert.

    In: Solar Physics, Vol. 289, No. 9, 01.01.2014, p. 3457-3481.

    Research output: Contribution to journalArticle

    Nagashima, K, Löptien, B, Gizon, L, Birch, AC, Cameron, R, Couvidat, S, Danilovic, S, Fleck, B & Stein, R 2014, 'Interpreting the Helioseismic and Magnetic Imager (HMI) Multi-Height Velocity Measurements', Solar Physics, vol. 289, no. 9, pp. 3457-3481. https://doi.org/10.1007/s11207-014-0543-5
    Nagashima K, Löptien B, Gizon L, Birch AC, Cameron R, Couvidat S et al. Interpreting the Helioseismic and Magnetic Imager (HMI) Multi-Height Velocity Measurements. Solar Physics. 2014 Jan 1;289(9):3457-3481. https://doi.org/10.1007/s11207-014-0543-5
    Nagashima, Kaori ; Löptien, Björn ; Gizon, Laurent ; Birch, Aaron C. ; Cameron, Robert ; Couvidat, Sebastien ; Danilovic, Sanja ; Fleck, Bernhard ; Stein, Robert. / Interpreting the Helioseismic and Magnetic Imager (HMI) Multi-Height Velocity Measurements. In: Solar Physics. 2014 ; Vol. 289, No. 9. pp. 3457-3481.
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