High-resolution modeling of the far infrared

Monochromatic calculations have been used to ascertain the far-infrared (wave numbers less than 650 cm-1) contribution to the thermal energy budget of the Earth's atmosphere-surface system. The results of the model calculations for clear-sky conditions have demonstrated that nearly half of the outgoing thermal energy emanates from the far-infrared. Despite the critical importance of the far- infrared, however, very few direct measurements of this spectral region have been made by satellite, aircraft, and surface instruments. Thus the present study has used the monochromatic calculations both to quantify the magnitude of the radiative impact which the infrared-active molecules have upon the absorption and emission of far-infrared energy within the atmosphere, and to focus our attention on the subintervals within the far-infrared that may provide the most useful measurements for climate studies. The results of the monochromatic calculations have illustrated the importance of the radiative effects attributed to the line and continuum features associated with the pure rotation band of water vapor. Subdividing the far-infrared into moderately narrow band (~100 to 200 cm-1) spectral regions has facilitated an analysis of the relative contributions of those spectral regions for a variety of atmospheric conditions. The results from the contribution function calculations have demonstrated that a careful selection of the far-infrared narrow band subintervals can prove very useful in determining both upper and lower tropospheric humidity.