  Based on the chiral kinetic approach using quarks and antiquarks from a
multiphase transport model as initial conditions, we study the chiral magnetic
effect, i.e., the magnetic field induced separation of charged particles in the
transverse plane, in non-central isobaric collisions of Zr$+$Zr and Ru$+$Ru,
which have the same atomic number but different proton numbers. For the
observable $\gamma^{OS}-\gamma^{SS}$ related to the difference between the
correlations of particles of opposite charges and of same charges, we find a
difference between the two collision systems if the magnetic field has a long
lifetime of 0.6 fm$/c$ and the observable is evaluated using the initial
reaction plane. This signal of the chiral magnetic effect becomes smaller and
comparable to the background contributions from elliptic flow if the event
plane determined from particle emission angles is used. For the other
observable given by the $R(\Delta S)$ correlator related to the distribution of
average charge separation in a collision, the signal due to the chiral magnetic
effect is found to depend less on whether the reaction or event plane is used
in the analysis, and their difference between the two isobaric collision
systems is thus a more robust observable.
