1. CAVIAR – Continuum Absorption by Visible and Infrared Radiation and its Atmospheric Relevance PI: Keith Shine Department of Meteorology, University of Reading Co-Is: Stephen Ball Department of Chemistry, University of Leicester Tom Gardiner National Physical Laboratory Roderic Jones Department of Chemistry, University of Cambridge John Harries, Juliet Pickering Blackett Laboratory, Imperial College London Kevin Smith Rutherford Appleton Laboratory, STFC Jonathan Taylor and Stuart Newman Met Office Jonathan Tennyson Department of Physics, University College London Co-ordinator: Igor Ptashnik Dept of Meteorology, Univ of Reading And (roughly!) 5 post-doc researchers and 3 PhD students

2. We know … Water vapour is by far the most important greenhouse gas in the atmosphere; we know it is important for remote sensing; we know it is an important contributor to climate feedbacks We also know … That it possesses a radiatively-important continuum, pervasive from the visible to microwave, which is represented in many models in a semi-empirical way, using observations from a limited number of wavenumbers and measurement conditions

3. Major Aims Describe the continuum across a broad wavelength range and a broad range of atmospheric and near- atmospheric conditions, using both laboratory and field measurements Explain the underlying cause of the continuum – can we separate out far-wing line shape contributions from dimer explanations? Provide the community with an improved continuum model (perhaps in a CKD-like form) visible near IR mid IR far IR Measurements

4. WP1 Molecular Modelling WP2 Laboratory Measurements WP3 Field Measurements WP4 SynthesisEveryone! WP5 Impact on Understanding WP6 Provision of model for wider use Everyone! The Programme

5. The work flow line-by-line radiative transfer models existing continuum models existing spectral line databases targeted lab measurements field campaigns Instrument upgrades and calibration dimer model development dimer model refinement new continuum model impact on understanding of atmospheric processes, incl climate and remote sensing preparation of continuum model for community use synthesis refinement of line database Work commenced or completed… Work soon commencing! …

6. The Project Formally, we started on 1 October 2006 … will formally end 30 June 2011 (including a no-cost extension) Annual meetings with international involvement

7. Major progress in third year: 1 First version of an improved ab-initio calculations of the dimer spectra First paper on continuum measurements across most of near-IR

8. Major progress in third year: 2 Advances in the broadband cavity- ringdown and cavity-enhanced methodologies and new results Is there or is there not a dimer signal in the visible …?

9. Major progress in third year: 2 A new high pressure/high temperature cell in operation … accessing the windows

10. Major progress in third year: 3 A major field campaign using aircraft and ground- based high-spectral resolution spectrometers, over the Jungfraujoch and continued analysis of previous years Camborne campaign

11. Challenges for fourth year: 1 Refinement of new ab initio dimer spectrum and comparison with measurements Full analysis of laboratory measurements using both traditional FTS and cavity – a particular emphasis will be on the between-band absorption, as this is most important for the AR in CAVIAR

12. Challenges for fourth year: 2 Full analysis of Camborne and Jungraujoch Field Campaigns

13. Challenges for fourth year: 3 Begin focused work on the three remaining workpackages: Synthesis of lab and field measurements and theoretical work Modelling the impact of the continuum on the radiation balance Developing a continuum model for community use without continuum with continuum

14. Conclusions The legacy of the project: - extensive new set of observations over a wide range of conditions in both lab and field - new physically-based continuum model with wide range of potential users – in basic science, in weather and climate prediction and in remote sensing - cohort of post-docs and students trained in a cross-disciplinary environment