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

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

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

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

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 … Work soon commencing! …

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

Major progress in second year: 1 Development of a new potential energy surface for water dimer, which will allow improved ab-initio calculations of its spectra Analyses of new laboratory measurements to derive the continuum across the near-infrared

Major progress in second year: 2 Advances in the broadband cavity- ringdown and cavity-enhanced methodologies and new results A major calibration exercise so that all CAVIAR field instrumentation are now traceable to the same standard

Major progress in second year: 3 A major field campaign using aircraft and ground-based high-spectral resolution spectrometers, plus supporting data Photo from Liam Tallis

Challenges for third year: 1 Production of new ab initio dimer spectrum and comparison with measurements New laboratory measurements using both traditional FTS and cavity – a particular emphasis will need to be on the between- band absorption, as this is most important for the AR in CAVIAR

Challenges for third year: 2 Analysis of new laboratory measurements Full analysis of calibration of field instruments Full analysis of Camborne Field Campaign The second field campaign at Jungfraujoch in summer 2009

Challenges for third year: 3 Begin serious 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 Clough et al. J.Geophys.Res, 1992

Conclusions In Year 2, we have made significant progress in model and instrument development, acquired and analysed new laboratory data, performed the major Camborne field experiment, and have advanced plans for the Jungfraujoch 2009 campaign 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