Improving the Modeling of Oxygen-Band Absorption: A Model-Measurement Comparison

The Atmospheric Radiation Measurement (ARM) program maintains a suite of instruments in various locations to provide continuous monitoring of atmospheric parameters. Temperature and humidity retrievals are some of the key parameters used by the climate modeling community. Accuracy in the spectroscopy adopted by the various radiative transfer models is crucial to adequate retrievals. While accuracy in the lines used for water vapor retrievals is satisfactory, temperature retrievals continue to be affected by discrepancies between modeled and observed brightness temperatures. In this paper, we compare model calculations in the oxygen-band channels with measurements collected by the ARM-operated 12-channel microwave radiometer (MWRP). The dataset used spans a wide range of atmospheric temperature conditions, with ground temperatures varying between -40degC and +40degC. Model calculations are performed using line parameters from the HITRAN database, from the MPM92-Rosenkranz database and from a set of newly published parameters. Our comparison shows that the newly published parameters improve the agreement with the measurements and confirms the need to update the HITRAN database for the oxygen lines. We show that differences between modeled and measured brightness temperatures are temperature dependent. To test the effect of the new line parameters on retrievals, we retrieve temperature profiles using the original HITRAN parameters and the updated parameters. We then compare results with ARM statistical retrievals