A template of atmospheric molecular oxygen circularly polarized emission
  for CMB experiments
  We compute the polarized signal from atmospheric molecular oxygen due to
Zeeman effect in the Earth magnetic field for various sites suitable for CMB
measurements such as South Pole, Dome C (Antarctica) and Atacama desert
(Chile). We present maps of this signal for those sites and show their typical
elevation and azimuth dependencies. We find a typical circularly polarized
signal (V Stokes parameter) level of 50 - 300 \mu K at 90 GHz when looking at
the zenith; Atacama site shows the lowest emission while Dome C site presents
the lowest gradient in polarized brightness temperature (0.3 \mu K/deg at 90
GHz). The accuracy and robustness of the template are tested with respect to
actual knowledge of the Earth magnetic field, its variability and atmospheric
parameters.
