"Roobik" Is Part of the Answer, Not a Puzzle

Turner, D. D., National Oceanic and Atmospheric Administration

Radiation Processes

Radiative Processes

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Taking place during the arid Arctic winter, the RHUBC will obtain measurements in the far-infrared (15-40 microns), when the so-called "Arctic" infrared window between 16 and 40 microns is semi-transparent.

Between February and March 2007 at the ACRF North Slope of Alaska site in Barrow, high-spectral-resolution observations will be collected by three state-of-the-art Fourier Transform Spectrometers sampling at different bands in the far-infrared. The Radiative Heating in Underexplored Bands Campaign, or RHUBC (pronounced "roobik"), will make detailed observations of the downwelling infrared radiation in the 17 - 100 µm and 6 - 7 µm spectral regions. These spectral bands are largely underexplored because they are normally opaque from the surface due to strong absorption by water vapor. Only when the atmosphere is semi-transparent can observations in these spectral regions be obtained.

Radiative cooling and heating in the mid-to-upper troposphere contribute significantly to the dynamical processes and radiative balance that regulate Earth's climate. In the longwave part of the spectrum, the dominant agent of this radiative cooling is water vapor. Due to the much greater abundances of water vapor at lower levels of the atmosphere, the spectral regions in which the mid-to-upper tropospheric cooling occurs are opaque when viewed from the vast majority of surface locations. Thus, the opacity of the lower atmosphere is a formidable obstacle in evaluating radiative processes important in the mid-to-upper troposphere. However, an even more substantial obstacle has been the lack of far-infrared radiometric instrumentation. Recent advances in instrumentation for measuring spectral radiation in the far-infrared region of the electromagnetic spectrum now allow the evaluation of radiative processes in the mid-to-upper troposphere (between 19,000 and 36,000 feet) that are crucial to understanding their effect on climate.

The RHUBC field campaign has a number of goals. First, it will allow collection of a robust set of measurements corresponding to low precipitable water vapor and cold temperatures; these are unobtainable in the laboratory. When used in clear-sky radiative closure studies, these data will reduce key uncertainties in water vapor spectroscopy, including the foreign-broadened water vapor continuum and water vapor absorption line parameters. Second, it will provide cross-calibration and validation of the three spectrometers for the purpose of atmospheric radiative transfer studies. None of these instruments have been validated relative to a similar instrument in an operational environment, so the intercomparison will provide higher confidence in the results from all three instruments. And third, the combination of spectrometers will obtain, for the first time ever, a simultaneous high-resolution dataset of Arctic cirrus emissions in the far-infrared. Ultimately, information gathered from the RHUBC field campaign will increase the knowledge base of mid-to-upper tropospheric radiative processes, leading to improved model simulations of future climate.