  We study ionization of atoms in strong elliptically-polarized laser fields
numerically and analytically. We focus on effects of laser ellipticity on the
offset angle in photoelectron momentum distribution. This angle is considered
to encode time information of tunneling ionization in attoclock experiments.
The calculated offset angle increases with the decrease of ellipticity but the
momentum along the major axis of laser polarization related to this angle
changes slowly, in agreement with experiments. With a Coulomb-included
strong-field model, the scaling laws for ellipticity dependence of this angle
and relevant momentum components are obtained, and the ellipticity dependence
of Coulomb-induced ionization time lag encoded in this angle is also addressed.
