1. The impact of water vapour continuum on absorption of solar radiation – a preliminary analysis of the impact of the new RAL measurements Julie Chenery, Igor Ptashnik, Keith Shine Department of Meteorology, University of Reading September 2010

2. (More than) a hint that (MT)-CKD is incorrect by an order of magnitude in near-IR windows Measurements in near-IR band wings Paynter et al. (JGR 2009) plus other evidence

3. Latest results support earlier preliminary measurements Measurements at RAL (Smith, McPheat,Williams) Analysis by Igor Ptashnik

4. 430 K measurements and comparison with MT-CKD

5. Method Apply 430 K ratio at all temperatures Clear sky, no scattering, near-IR only, includes CO 2, CH 4 etc From previous work (Ptashnik, Paynter, …) we do not expect a huge effect

6. Vertical optical depth in near-IR for mid-lat summer atmosphere

7. Impact on surface irradiance (overhead sun) mainly seen at edges of windows

8. Dependence on solar zenith angle 0 o 85 o

9. Dependence on zenith angle Marked difference in dependence between the two continua

10. Dependence on atmosphere New Old 0o0o 85 o

11. July latitudinal dependence Absolute (0.6%) (0.4 Wm -2 )

12. Next steps Update continuum with more recent analyses including refined temperature dependence Include band centres Extend to cloudy skies etc. Possibly extend to examining impact on water vapour feedbacks in response to climate change