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Table 1.

Summary of the main quantities defined in the paper.

Quantity Background Perturbations
Intensity Iλ Iλ0 Eq. (1) δIλ = δIgeom + δIth + δIline
Eqs. (21), (25), and (25)
HMI filtergrams ℐj (1 ≤ j ≤ 6) j0 (Eq. (5) with I0λ) δj (Eq. (5) with δIλ)
Fourier coefficients a1 and b1 a10, b10 (Eqs. (7), (8) with ℐj0) δa1, δb1 (Eqs. (7), (8) with δj)
Velocity v (before lookup table) v0 (Eq. (26)) δv (Eq. (27))

vHMI (corresponding to hmi.V_45s) vHMI0 (Eq. (29)) δvHMI (Eq. (30))
=δvgeom + δvth + δvline (from δIgeom, δIth, δIline)
Line-of-sight flow velocity vlos0 (Eq. (18) ) δvlos (approximation at fixed height, Eq. (40))

IHMI (corresponding to hmi.Ic_45s) IHMI0 (Eq. (12) with ℐj0) δIHMI (Eq. (36))
Continuum intensity Ic Ic0 (=Iλ0 for λ in continuum) δIc (=δIλ for λ in continuum)

Notes. The perturbed HMI velocity δvHMI is compared to the approximation δvlos, and the HMI continuum δIHMI is compared to the pure continuum δIc.

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