  We propose to detect the interference effect between the atmospheric-scale
and solar-scale waves of neutrino oscillation, one of the key consequences of
the three-generation structure of leptons. In vacuum, we show that there is a
natural and general way of decomposing the oscillation amplitude into these two
oscillation modes. The nature of the interference is cleanest in the
$\bar{\nu}_e$ disappearance channel since it is free from the CP-phase
$\delta$. We find that the upcoming JUNO experiment offers an ideal setting to
observe this interference with more than $4\,\sigma$ significance, even under
conservative assumptions about the systematic uncertainties.
