An assessment of recent water vapor continuum measurements upon longwave and shortwave radiative transfer

Abstract

[1] Recent measurements of the water vapor continuum have been combined to form an empirical continuum termed the BPS continuum model. This covers the 800 to 7500 cm−1 spectral region for the self continuum and most of the major absorbing spectral regions between 240 and 7300 cm−1 for the foreign continuum. Longwave (i.e., absorption/emission of terrestrial radiation between 1 and 3000 cm−1) and shortwave (i.e., using solar radiation as a source and considering atmospheric absorption between 1000 and 17000 cm−1) line by line (LBL) radiative transfer calculations have been performed for clear-sky conditions in three standard test atmospheres using line data from the HITRAN database. This has allowed BPS to be compared to the commonly used CKD and MT CKD continuum models, in addition to conducting a more detailed investigation of the separate roles of the self and foreign continua than previously provided in the literature. Using uncertainties obtained from multiple experimental studies it has been possible to estimate the upper and lower limits of the effects due to the continuum in many spectral regions. The outgoing longwave radiation in a midlatitude-summer (MLS) atmosphere calculated by all three continuum models agree to within 0.6 Wm−2 with a ±1.1 Wm−2 estimated uncertainty. The corresponding values for surface downwelling radiation are 1.3 Wm−2 ± 2.5 Wm−2. For shortwave absorption, the different models agree within 1.0%, with an estimated uncertainty of ±1.7%. However, the three models differ in the amount by which the self and foreign continua contribute to shortwave absorption.