1. 16 December 2008 CAVIAR Annual Meeting 2008 1 Claudine Chen and John E Harries Claudine Chen and John E Harries Space and Atmospheric Physics group, Blackett Laboratory, Imperial College, London,UK Initial calculations of continuum effect on outgoing IR spectrum: Preparations for CAVIAR WP 5

2. 16 December 2008 CAVIAR Annual Meeting 2008 2 Earth spectrum studies at Imperial and a view for the future At Imperial College for over a decade, we have studied the information contained in the Earths outgoing infrared spectrum, with a view to exploiting this information to study the changing climate. We have used model simulations and real observations, and more recently re-analysis data. We have focussed attention on the far IR. Now we are looking at future missions, such as CLARREO*, which seek to measure the spectrally resolved energy flux into and out of the planet, and the setting up in space of a measurement standard satellite, capable of inter-calibrating other missions. * (Climate and Absolute Radiance and Refractometry Observatory)

3. 16 December 2008 CAVIAR Annual Meeting 2008 3 The CAVIAR component of this project: As part of this study of the Earths IR spectrum, we have simulated the effect of the Continuum absorption on the OLR spectrum of the Earth. We have used MT CKD v1.3 of the continuum, in the LBLRTM code v10.3 to simulate the OLR spectrum, with and without the continuum. We have used the NCEP re-analysis to provide atmospheres as input to the RT code. ERA-40 atmospheres will also be used, and ERA-Interim is also being introduced. We report here only the initial results using NCEP.

4. 16 December 2008 CAVIAR Annual Meeting 2008 4

5. 16 December 2008 CAVIAR Annual Meeting 2008 5

6. 16 December 2008 CAVIAR Annual Meeting 2008 6 Pure rotation H2O CO2 CH4 O3 (highly variable) 2 H2O

8. 16 December 2008 CAVIAR Annual Meeting 2008 8 Summary We have simulated the effect of the continuum absorption on the OLR spectrum of the Earth using LBLRTM v10.3, which uses MT-CKD v1.3, using NCEP reanalysis data as input Water continuum contributes to almost 10% of the radiance for profiles over the tropical oceans in the window region and pure rotation band The water continuum is also potentially significant when looking at time evolution and future projections. In this case, water continuum contributed a radiative forcing of ~0.5 W/m 2 to the difference signal