TES observations of tropospheric ozone as a greenhouse gas

We present satellite observations of the downward radiative flux from tropospheric ozone, for cloud free ocean conditions. This analysis uses infrared (IR) radiance spectra, integrated over the 9.6 micron ozone band between 985 to 1080 cm-1, and ozone profile retrievals from the Tropospheric Emission Spectrometer (TES) on EOS-Aura. We examine the sensitivity of the outgoing longwave radiation (OLR) in the 9.6 micron band to upper tropospheric ozone and water vapor by separating the data into hemispherical and sea-surface temperature (SST) ranges. For 2006 data, we estimate an annual average downward flux for upper tropospheric ozone of 0.48 ± 0.13 W/m2 with a standard deviation of 0.24 W/m2 for the latitude range between 45°S to 45°N. This estimate includes natural and anthropogenic ozone sources and is higher than the 2007 IPCC average for climate model estimates of anthropogenic tropospheric ozone radiative forcing of 0.35 W/m2. We also observe that water vapor dominates the clear-sky ocean variability of the outgoing IR radiation in the 9.6 micron ozone band for SSTs higher than 299 K, consistent with the "super greenhouse effect". This underscores the importance of chemistry-climate coupling in forcing predictions for tropospheric ozone.