Apparent surface radial velocity of solar gravity modes as a function of the oscillation frequency ν_nℓm and the angular degree ℓ, for azimuthal numbers m = ℓ and for standard plume parameters. The results obtained with a Gaussian and an exponential plume time evolution (see Sect. 2.3) are represented by the diamonds and the plus signs, respectively, for each considered eigenmode. The thick dashed gray line corresponds to the 22-year GOLF detection threshold (see Sect. 3.3). The blue dash-dotted line represents the upper limit for the amplitude of the dipolar modes when accounting for the largest plausible variations in the plume parameters (i.e., with a factor of two increase in the inverse plume lifetime and radius; see Sect. 4.3).