1. 1 Water vapour self-continuum in windows: Processing the recent MSF RAL measurements Igor Ptashnik University of Reading CAVIAR semi-annual meeting 29.09.2010 NPL, London

2. 2 Saturated P H2O (mb) T (K)P H2O (mb) 3530010(F), 20(F) 41635010(F), 50(F), 300 F 100037550(F), 400, 600 F,750 2500400 600 F,1000, 1500 F,2000 5700430 600 F,1000, 1500,2000, 3000, 4000 14000470 1000,2000, 3000, 4000, 5000 Resolution (cm -1 ): N of scans: 0.050.1 0.2 : 0.3 1000 500 MSF RAL measurements (R. McPheat, K. Smith, G. Willaims) Pure H2O measurements (self-continuum) 1) empty cell 2) Argon (same pressure as H 2 O in step 3) 3) pure H 2 O (same pressure as in step 2) 4) Argon (same pressure as H 2 O in step 3) 5) empty cell

3. 3 MSF RAL measurements (R. McPheat, K. Smith, G. Willaims) Optical depth Baseline error usually did not exceed 0.5% Spectral resolution high enough to resolve separate lines Baseline accuracy ILS

4. 4 Processing MSF RAL measurements Continuum small as compared to the lines in microwindows Continuum is strong as compared to the lines in microwindows

5. 5 Processing MSF RAL measurements Retrieved experimental self-continuum in windows is an order of magnitude stronger than MTCKD in model. For 2500 cm -1 and 4600 cm -1 windows the disagreement increases with temperature, reaching a factor 25 at 470 K.

6. 6 There is a reasonably good agreement with the previous high-T measurements by Burch & Alt (1984) and Hartmann et al. (19993). However, at lower T-s Burch's data starts underestimating continuum, while Baranov & Lafferty data is a factor 2 higher than ours at 350K. Processing MSF RAL measurements Baranov & Lafferty, 350 K

7. 7 Temperature dependence. Simple analysis.

8. 8

9. 9 Slope (i.e. D o ) is varying: from max - 1770 K (2400-2600 cm -1, lower T-s; 6200-6400 cm -1, higher T-s); to min - 600 K (2500-6000 cm -1, higher T-s). Slope (i.e. Do): 1770 K – max slope (6200 cm -1, high T); 1066 K (5900 cm -1 ); 587 K (2500 cm-1, high T); 1030 K (2500 low T); 1713 K (2600 cm, 2 lowest T); 1800 K (Baranov)