  We report the results of a statistical analysis performed with the four
foreground-cleaned Planck maps by means of a suitably defined {\it
local-variance} estimator. Our analysis shows a clear dipolar structure in
Planck's {\it variance map} pointing in the direction $(l,b) \,\simeq\,
(220^{\circ},-32^{\circ})$, thus consistent with the North-South asymmetry
phenomenon. Surprisingly, and contrary to previous findings, removing the CMB
quadrupole and octopole makes the asymmetry stronger. Our results show a
maximal statistical significance, of $98.1\%$ CL, in the scales ranging from
$\ell=4$ to $\ell=500$. Additionally, through exhaustive analyses of the four
foreground-cleaned and individual frequency Planck maps, we find unlikely that
residual foregrounds could be causing this dipole variance asymmetry. Moreover,
we find that the dipole gets lower amplitudes for larger masks, evidencing that
most of the contribution to the variance dipole comes from a region near the
galactic plane. Finally, our results are robust against different foreground
cleaning procedures, different Planck masks, pixelization parameters, and the
addition of inhomogeneous real noise.
