Atmospheric neutrino experiments have been studying
νμ→ντ oscillations extensively.
The zenith angle and energy dependent deficit,
or more recently the L/E dependent deficit, of atmospheric muon neutrinos
has been used to constrain the neutrino oscillation parameters:
sin22θ23>0.9 and 1.9<Δm232<3.0x10-3 eV2.
As a natural extension of the present νμ→ντ oscillation studies, atmospheric neutrino experiments should study three
flavor oscillation effects. One is the effects driven by θ13 and
the other is the ones driven by the solar oscillation terms (θ12 and Δm122). Especially,
thanks to the diameter of the Earth, atmospheric neutrino experiments are,
in principle, sensitive to the solar neutrino oscillation terms. If the solar neutrino oscillation
effect is observed, it is possible to get unique information, such as a
discrimination of θ23 larger or smaller than 45degree for non-maximal
sin22θ23.
It is predicted that the effect of solar neutrino oscillations
on atmospheric neutrino experiments is relatively a small effect, and improvements
of the accuracy of our understanding of the flux and the neutrino interaction
cross sections are required. In addition, very careful evaluations of the
systematic uncertainties are required. These topics will be discussed in
detail in this workshop.