Recent progress in spectroscopy and its effect on line-by-line calculations for the validation of radiation codes for climate models

• Published in: Atmospheric and oceanic optics 2009-12, Vol.22 (6), p.626-629
• Main Authors: Fomin, B. A., Falaleeva, V. A.
• Format: Article
• Language: English
• Subjects: Lasers; Optical Devices; Optical Sources and Receivers for Environmental Studies; Optics; Photonics; Physics; Physics and Astronomy
• ISSN: 1024-8560; 2070-0393
• DOI: 10.1134/S1024856009060086

The evolution of spectroscopic data from 2008 to 2009 and its effect on line-by-line (LBL) calculations for the validation of radiation codes for climate models is the subject matter of this paper. The authors have used the standard midlatitude summer (MLS) atmosphere in all numerical experiments. Long-wave calculations with the current (2008) and previous (2002) HITRAN variations revealed a very good agreement between them: the discrepancies are less than ∼0.1 W/m 2 in flux calculations (H 2 O, CO 2 , and O 3 lines and continuums). The replacement of the latest (MT CKD-2.1) version by the previous one (CKD-2.4) gave a discrepancy of up to ∼0.9 W/m 2 . The shortwave calculations with the same HITRAN versions, on the contrary, have revealed a disagreement greater than that observed during the previous decade: the additional absorption only in the water vapor lines in the downward fluxes has reached 2.6 and 2.1 W/m 2 (∼1.5 and 2.9%) for solar zenith angles (SZA) of 30° and 75°, respectively. The additional absorption with the latest and previous HITRAN versions along with the continuum models has reached 2.0 and 0.4 W/m 2 for SZA of 30° and 75°, respectively (H 2 O, CO 2 , O 2 , and O 3 lines and continuums). It has been found that the total neglect of the line-mixing effect can produce essential errors of about 2.5 W/m 2 (1.5%) in the long-wave flux calculations. Nevertheless, their usual treatment with the use of a line shape correction or first-order approximation gave a satisfactory result: the errors in the long-wave flux calculations were below ∼0.14 W/m 2 (∼0.1%) and ∼0.03 W/m 2 , respectively.