Trends in Downwelling Spectral Infrared Radiances at SGP

Downwelling longwave radiation (DLR) is an important part of the surface energy budget. Identifying the trends of downwelling spectral infrared radiances is crucial because it can help us understand the downwelling radiation variability in relation to meteorological fields.

In this research, we apply a trend analysis based on the weighted linear regression method to the 17-year downwelling longwave radiances measured by the Atmospheric Emitted Radiance Interferometer (AERI) at the ARM Southern Great Plains (SGP) site. Two AERIs were deployed at SGP with 10 years' overlapping observations, which allows us to examine the consistency and accuracy of the measurements. In addition, we use clear-sky LBLRTM simulations as a proxy to verify the consistency between the radiance measurements and the collocated meteorological conditions and to determine appropriate weights of the monthly DLR spectra observed by the two AERIs for the trend detection. We find that the radiance trends at SGP are generally positive in the infrared spectral range measured by AERI and the largest in the window band. These trends are attributed, with the aid of the kernel and fingerprinting methods, to meteorological variables, such as water vapor, temperature and clouds.