Comparison of band model calculations of upper atmospheric cooling rates for the 15‐micrometer carbon dioxide band

Abstract

Comparisons are made between cooling rates for the CO2 15‐μm band in the middle to upper stratosphere (30–50 km) that were calculated by three widely used methods for handling infrared emission and absorption: an emissivity parameterization, a band absorptance formulation, and an “exact” line‐by‐line calculation. Cooling rates are presented for two temperature distributions—the U.S. Standard Atmospheric profile and a polar sounding. The band absorptance approach adopts Ramanathan's approximate treatment to account for transition of line shapes to Doppler broadening in the upper stratosphere but employs a new Doppler band model which yields better agreement with more detailed calculations. For both temperature profiles, cooling rates obtained by all three methods show good agreement with one another, differing by less than 0.5 K/day below 50 km. Above 50 km, variations among the cooling rates increase slightly to 0.5–1 K/day. At the stratopause, these differences correspond to a temperature error of 2 to 4 K.