Three flavor neutrino oscillation analysis of the Superkamiokande atmospheric neutrino data

Superkamiokande atmospheric neutrino data for 535 days are analyzed in the framework of three flavor oscillations with mass hierarchy. It is shown that the best fit point is very close to the pure maximal ${\nu }_{\mu }\leftrightarrow {\nu }_{\tau }$ case and $\mathrm{\Delta }{m}^2\simeq 7\times {10}^{-3}$ eV${}^2$. The allowed region at 90 %CL is given and the implications to the long baseline experiments are briefly discussed.