Table 2.
Summary of the nature, wavelength, and formation height of the absorption line used by the instruments considered in this paper.
| Instrument | Line | λ (Å) | Height (km) |
|---|---|---|---|
| MDI/GONG | Ni I | 6768 | 170 |
| GOLF | Na I D1/D2 | 5896/5890 | 340 |
| HMI | Fe I | 6173 | 100 |
Notes. The formation heights are given with respect to the photosphere. References: Fleck et al. (2011; MDI/GONG, HMI) and Baudin et al. (2005; GOLF). Note that the MDI instrument and the GONG network use the same spectral line and therefore observe the modes at the same altitude.
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