Observing CMB polarisation through ice
  Ice crystal clouds in the upper troposphere can generate polarisation signals at the uK level. This signal can seriously affect very sensitive ground based searches for E- and B-mode of Cosmic Microwave Background polarisation. In this paper we estimate this effect within the ClOVER experiment observing bands (97, 150 and 220 GHz) for the selected observing site (Llano de Chajnantor, Atacama desert, Chile). The results show that the polarisation signal from the clouds can be of the order of or even bigger than the CMB expected polarisation. Climatological data suggest that this signal is fairly constant over the whole year in Antarctica. On the other hand the stronger seasonal variability in Atacama allows for a 50% of clean observations during the dry season. 
Luca Pietranera, Stefan Buhler, Paolo G. Calisse, Claudia Emde, Darren   Hayton, Viju Oommen John, Bruno Maffei, Lucio Picci...