  The terahertz and far-infrared (FIR) band, from approximately 0.3 THz to 15
THz (1 mm to 20 micron), is important for astrophysics as the thermal radiation
of much of the universe peaks at these wavelengths and many spectral lines that
trace the cycle of interstellar matter also lie within this band. However,
water vapor renders the terrestrial atmosphere opaque to this frequency band
over nearly all of the Earth's surface. Early radiometric measurements below 1
THz at Dome A, the highest point of the cold and dry Antarctic ice sheet,
suggest that it may offer the best possible access for ground-based
astronomical observations in the terahertz and FIR band. To address uncertainty
in radiative transfer modelling, we carried out measurements of atmospheric
radiation from Dome A spanning the entire water vapor pure rotation band from
20 micron to 350 micron wavelength by a Fourier transform spectrometer. Our
measurements expose atmospheric windows having significant transmission
throughout this band. Furthermore, by combining our broadband spectra with
auxiliary data on the atmospheric state over Dome A, we set new constraints on
the spectral absorption of water vapor at upper tropospheric temperatures
important for accurately modeling the terrestrial climate. In particular, we
find that current spectral models significantly underestimate the H2O continuum
absorption.
