We explore the concept of a retrieval of the thermal infrared radiative flux divergence and cooling rate profile using top-of-atmosphere spectral radiance measurements and demonstrate that the retrieval of this quantity can be performed directly. We show that the inversion encountered in this problem is sensitive to the initial atmospheric state vector assumed a priori. However, the direct approach has specific advantageous in terms of accuracy and computational speed, as compared to the conventional indirect approach using the retrieved atmospheric state vector coupled with a line-by-line radiative transfer model in cooling rate calculations. Furthermore, we show that the spectrally-resolved radiative forcing at the tropopause can be derived directly from the retrieved flux-divergence profile. As a test case, we carried out retrieval in the strong cooling band associated with the 15 μm band of CO₂ employing the Atmospheric Infrared Sounder (AIRS, 2002-present) on board the Aqua satellite, along with validation campaign data and under-flight Scanning High-Resolution Interferometer (S-HIS) zenith and nadir spectra taken aboard a high-altitude aircraft. Retrieval sensitivity analyses have been performed for AIRS and the Infrared Interferometer Sounder (IRIS-D, 1970-1971) instruments. It is anticipated that the large changes in stratospheric temperature and CO₂ values between the two missions would lead to detectable changes in the CO₂ radiative forcing at the tropopause so long as the IRIS-D instrument could be appropriately characterized.

What's  New

• AGU Poster Session on December 8, 2005
  • Poster PPT version (3.7 MB)
  • Poster PDF version (780 KB)

• Future Work
  • Cooling Rate Tropopause Error Budget