Neutrinos oscillate, and their oscillations are different when propagating in matter than in vaccum. The two oscillation frequencies are called '12' or solar, and '13' or atmospheric.

The length of the blue line is the probability amplitude for each of the two sectors. The amplitude squared gives the probability.

The horizontal and time axis scale with the matter potential (which is proportional to the neutrino energy). As the potential increases, at a certain point, shows the resonance when the probability hits a minimum.

Triangle 12 gif
Triangle 13 gif
For an experiment near maximum at Δ32=0.4π. For δCP near maximum, the amplitude is maximally different between neutrinos and anti-neutrinos, while they are the same for δCP=0,π.
Triangle Amue gif

See arXiv:1604.08167 for more information.