Improved Understanding of Far-Infrared Radiative Processes Using Measurements from the ARM North Slope of Alaska Climate Research Facility

Far-infrared radiative cooling in the mid-to-upper troposphere due to water vapor contributes significantly to the dynamical processes and radiative balance that regulate Earths climate. In the spring of 2007, the Radiative Heating in Underexplored Bands Campaign-I (RHUBC-I) was conducted at the Atmospheric Radiation Measurement Programs North Slope of Alaska Climate Research Facility. The experiment was designed to make detailed observations of downwelling infrared radiation in the pure rotation band of water vapor under extremely dry and cold conditions, which in many ways are similar to those found in the mid-to-upper troposphere. State-of-the-art 183 GHz microwave radiometers were also simultaneously deployed to provide the highly accurate retrievals of precipitable water vapor (PWV) that are required for the farinfrared radiative closure studies. With numerous radiosondes launched in conditions with less than 3 mm of PWV, RHUBC provided the opportunity for extensive clear-sky, high spectral-resolution comparisons between measurements and the line-by-line radiative transfer model LBLRTM. This presentation will discuss results from the RHUBC-I campaign. Specifically, we will present comparisons between LBLRTM calculations and extended-range Atmospheric Emitted Radiance Interferometer (AERI) longwave radiance observations in the far-infrared from 400 to 650 cm_1 . Analysis of the far-infrared spectral residuals has led to modifications to the MT CKD water vapor foreign continuum model and adjustments to spectral line parameters relative to the current version of HITRAN. Results from the measurement-model intercomparison at 183 GHz will also be presented.