SPT-3G: Measurement and Mitigation of mm-wave Polarized Atmospheric Emission

Ground-based detection of inflationary B-mode polarization with cosmic microwave background (CMB) experiments requires a detailed understanding of contaminating signals. B-mode power spectrum forecasts and simulations generally assume the atmosphere to be unpolarized, but this is not always the case. Polarized atmospheric emission has previously been reported by both the CLASS and POLARBEAR experiments in the Atacama Desert in Chile. This polarized radiation is thought to arise from a population of horizontally aligned ice crystals in the atmosphere, which scatter thermal radiation from the ground and contribute thermal emission. This creates a time-varying, anisotropic, horizontally polarized signal that is most prevalent at the large angular scales relevant to inflationary B-modes (> 0.5 degrees). I will present the first detection of polarized atmospheric emission at the South Pole using the South Pole Telescope (SPT) and offer a complete theoretical description of the effect, as well as present a full measured amplitude distribution of the signal from four years of SPT-3G Austral winter data. I will conclude with mitigation strategies and the relevance of this model to CMB experiment design and forecasting.