Climate-Relevant Gas Absorption Properties from AWARE and Other ARM Spectral Measurements (Final Report)

Abstract

The objective of this project has been to use measurements from the Atmospheric Emitted Radiance Interferometer (AERI) deployed at ARM sites to improve our knowledge of uncertain infrared spectroscopic parameters of importance to climate, remote sensing, and data assimilation. A primary focus has been the water vapor continuum in the infrared atmospheric window. Radiation codes used to predict climate and weather base their representation of the water vapor continuum in this window on the MT_CKD model, but in this spectral region the MT_CKD water vapor continuum absorption coefficients were derived almost two decades ago by an analysis of AERI measurements for conditions with a limited range of precipitable water vapor (PWV) . We have performed a new, comprehensive analysis of all aspects of the water vapor continuum in the atmospheric window -- the self continuum, the foreign continuum, and the self continuum temperature dependence. Having a wide range of PWV amounts and temperatures from deployments of the ARM Mobile Facility for GoAmazon as well as the more than a decade of AERI measurements at SGP has provided an appropriate foundation for such a comprehensive analysis. This analysis has resulted in large changes to the self and foreign continuum than the values in the MT_CKD model, which may have significant implications for dependent applications. In addition, a secondary focus of this project has been on the evaluation and improvement of water vapor spectroscopy in the microwave. The standard specification of water vapor at ARM sites has involved modification of sonde water vapor profiles such that the profile is consistent with water vapor information obtained from microwave instruments measuring in the vicinity of water vapor absorption lines. Our project will lead to improvement in these specification. We also exploited the low PWV values associated with the RHUBC-II campaign to begin an analysis of the spectroscopic parameters in the infrared water vapor absorption band used for remote sensing and data assimilation of water vapor. This analysis is being combined with a complementary analysis of IASI satellite observations in this band. All improved water vapor continuum parameters that have been derived in this project have been implemented in the MT_CKD continuum model, and values that have not yet been finalized will also be included. Improvements will also be utilized by to the Line-By-Line Radiative Transfer Model (LBLRTM), and the fast radiation code RTE+RRTMGP. In addition, the accuracy of a number of standard ARM products will be enhanced by the improvements in spectroscopy resulting from our study, including the MWRRET PWV/LWP retrieval and AERIoe retrievals. RTE+RRTMGP is planned to be implemented in E3SM, CESM, and other atmospheric models, so the result of this project will lead to important improvements in the treatment of radiation in DOE-supported global and regional climate models.