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. 
Giulio Fabbian, Sebastiano Spinelli, Massimo Gervasi, Andrea Tartari,   Mario Zannoni
astro-ph.CO astro-ph.IM physics.ao-ph