Surface Forcing from CH4 at the North Slope of Alaska and Southern Great Plains Sites

Abstract:

Recent increases in atmospheric CH₄ have been spatially heterogeneous as indicated by in situ flask measurements and space-borne remote-sensing retrievals from the AIRS instrument, potentially leading to increased radiative forcing.

We present detailed, specialized measurements at the DOE ARM North Slope of Alaska (NSA) and Southern Great Plains (SGP) sites to derive the time-series of both CH₄ atmospheric concentrations and associated radiative implications at highly-contrasting natural and anthropogenic sources. Using a combination of spectroscopic measurements, in situ observations, and ancillary data for the atmospheric thermodynamic state from radiosondes and cloud-clearing from active sounders, we can separate out the contribution of CH₄ to clear-sky downwelling radiance spectra and its infrared surface forcing. The time-series indicates year-to-year variation in shoulder season increases of CH₄ concentration and forcing at NSA and large signals from anthropogenic activity at SGP.