  We present experimental data on the strong field tunnel ionization of argon
in a counter-rotating two-color (CRTC) laser field. We find that the initial
momentum component along the tunneling direction changes sign comparing the
rising and the falling edge of the CRTC field. If the initial momentum at the
tunnel exit points in the direction of the ion at the instant of tunneling,
this manifests as an enhanced Coulomb interaction of the outgoing electron with
its parent ion. Our conclusions are in accordance with predictions based on
strong field approximation.
