Xing, ZZ (reprint author), CCAST, World Lab, POB 8730, Beijing 100080, Peoples R China.
We show that the 3 x 3 lepton flavour mixing matrix V can be expanded in powers of a Wolfenstein-like parameter Lambda drop \V-mu3\ similar to 1/root2, which measures the strength of flavour conversion in atmospheric neutrino oscillations. The term of O(Lambda(2)) is associated with the large mixing angle in solar neutrino oscillations. The Dirac phase of CP violation enters at or below O(Lambda(8)), and the Majorana phases of CP violation are not subject to the A-expansion. Terrestrial matter effects on this new parametrization in realistic long-baseline neutrino oscillation experiments are briefly discussed. Some comments are also given on the possible relation between A and a relatively weak hierarchy of neutrino masses.