Outgoing Longwave Radiation Spectrum simulations from ERA-Interim

The spectrally resolved Outgoing Longwave Radiation (OLR) is the result of the complex interaction of the earth's emitted radiation with different geophysical variables at different altitudes. Although so far no instrument has observed the entire range of the Earth's Infrared (IR) emission, future missions with this objective are now being formulated (e.g. NASA CLARREO). It is thus of interest to examine the variability contained within the resolved OLR spectra as a function of space and time. The information on the state of the atmosphere given in ECMWF ERA-Interim re-analyses was used as input to a line by line radiative transfer model in order to run a series of simulations spanning over a 10 year period on a global scale. Individual OLR spectra between 100 and 2500 cm-1 were simulated with a spectral resolution of 0.5 cm-1. A database of these spectra at each ERA-Interim grid point was created at a monthly timestep from January 1999 to December 2008 corresponding to a grand total of 3,484,800 spectra over the full 10 years. We analyze the radiance evolution in the time and space domains, quantify the variability of the spectral signatures seen, and assess how the changes in key atmospheric variables (temperature, water vapor, ozone, carbon dioxide ...) affect the TOA emission at different wavelengths. Finally we evaluate how the signal variability in the simulations influences the ability and the time required to detect long term trends in the climate system by future space missions.