Analyzing Atmospheric Conditions for CMB Survey Planning*

Precision cosmological surveys of the cosmic microwave background (CMB) can be made from the ground from high-altitude sites with exceptional weather, including low levels of precipitable water vapor (PWV) and stable atmospheric conditions. Two established sites for CMB observations are the South Pole and Cerro Toco in the Atacama desert in Chile. While the South Pole offers optimal conditions for deep CMB surveys, its coverage is limited to less than 20% of the sky. The Atacama desert in Chile provides access to a larger portion of the sky but experiences more variable weather conditions. This study analyzes atmospheric and PWV variations using publicly available data from the Atacama Pathfinder Experiment (APEX) water vapor radiometer. We present a statistical assessment of over a decade of atmospheric data to understand trends in available observing time, and to inform instrument design.