  We test the asymmetry of the Cosmic Microwave Background anisotropy jointly
in temperature and polarization. We study the hemispherical asymmetry,
previously found only in the temperature field, with respect to the axis
identified by Hansen et al. (2009). To this extent, we make use of the low
resolution WMAP 5 year temperature and polarization Nside=16 maps and the
optimal angular power spectrum estimator BolPol (Gruppuso et al. 2009). We
consider two simple estimators for the power asymmetry and we compare our
findings with Monte Carlo simulations which take into account the full noise
covariance matrix. We confirm an excess of power in temperature angular power
spectrum in the Southern hemisphere at a significant level, between 3 sigma and
4 sigma depending on the exact range of multipoles considered. We do not find
significant power asymmetry in the gradient (curl) component EE (BB) of
polarized angular spectra. Also cross-correlation power spectra, i.e. TE, TB,
EB, show no significant hemispherical asymmetry. We also show that the Cold
Spot found by Vielva et al. (2004) in the Southern Galactic hemisphere does not
alter the significance of the hemispherical asymmetries on multipoles which can
be probed by maps at resolution Nside=16. Although the origin of the
hemispherical asymmetry in temperature remains unclear, the study of the
polarization patter could add useful information on its explanation. We
therefore forecast by Monte Carlo the Planck capabilities in probing
polarization asymmetries.
