Terahertz atmospheric transmission measured at the AliCPT site

Cosmic-microwave-background (CMB) B-mode measurements may reveal primordial gravitational waves from the earliest phases of the Big Bang. As the first CMB experiment in the northern hemisphere, the Ali CMB polarization telescope (AliCPT) will carry out measurements of this kind at Ali (Nagri) in Tibet. It is therefore of particular importance to understand the terahertz atmospheric transmission at this site. Here we report on the measurement results for three consecutive seasons with a Fourier transform spectrometer (FTS) spanning a wide frequency range from 0.75 to 14 THz. The zenith median precipitable-water-vapor (PWV) is found to be as low as 1 mm at the AliCPT site, which appears as good as those CMB B-mode measurement sites in the southern hemisphere such as Chile's Atacama Desert.

Automated summary

The Ali CMB polarization telescope (AliCPT) in Tibet will conduct B-mode measurements to detect gravitational waves in the cosmic microwave background (CMB) radiation. Measurement results from three consecutive seasons using a Fourier transform spectrometer (FTS) show that the AliCPT site has a zenith median precipitable water vapor (PWV) as low as 1 mm, comparable to CMB B-mode measurement sites in the southern hemisphere such as Chile's Atacama Desert.