1. ISSI Working Group on Atmospheric Water Vapor, 11 Feb 2008 Holger Vömel Cooperative Institute for Research in Environmental Sciences University of Colorado Water vapor observations using the CFH

2. Overview Science issues: Trend (stratosphere / upper troposphere) Supersaturation Use in forecasting and modelsScience issues: Trend (stratosphere / upper troposphere) Supersaturation Use in forecasting and models Measurement issues: Absolute accuracy In-cloud measurements Frostpoint above 0CMeasurement issues: Absolute accuracy In-cloud measurements Frostpoint above 0C Logistical issues: World wide coverage Instrument availability Cost Radiosonde manufacturer interactionLogistical issues: World wide coverage Instrument availability Cost Radiosonde manufacturer interaction

3. Cryogenic Frostpoint Hygrometer (CFH) Microprocessor control Microprocessor control Vertical Range: surface to ~28 km (surface to ~25 km on ascent) Vertical Range: surface to ~28 km (surface to ~25 km on ascent) Uncertainty: troposphere: > 4% MR stratosphere: ~ 9 % Uncertainty: troposphere: > 4% MR stratosphere: ~ 9 % Phase sensitive detector: electronic sunlight filter Phase sensitive detector: electronic sunlight filter No liquid/ice ambiguity No liquid/ice ambiguity Weight: ~ 400 gr Weight: ~ 400 gr Currently interfaced with ECC ozone sonde and Vaisala RS80 Currently interfaced with ECC ozone sonde and Vaisala RS80 >300 soundings >300 soundings Detector IR LED μ Controller Cryogen Air flow Lens Mirror Heater Frost layer Thermistor

4. Science issue: Trends

5. Boulder trend From Scherer et al., ACPD 2007

6. Boulder trend From Scherer et al., ACPD 2007

7. Where to measure trend? Processes controlling entry of water into stratosphere Methane oxidation and PSCs From Holton et al., Rev. Geophys. 1995

8. Science issue: Supersaturation

9. Supersaturation from WB-57 From Gao et al., Science, 2003

10. Harvard Lyman alpha - CFH

11. RH ice from tropical CFH soundings

12. Supersaturation in cloud

13. Measurement issue: Absolute accuracy

14. 2 4 6 8 10 12 14 Mixing Ratio (ppmv) 1 10 100 Pressure (hPa) Sep 2004 Sep 2005 Ft Sumner (~35ºN) Balloon comparisons Aura MLS / FIRS-2 / MkIV / NOAA FP 10 100 2 4 6 8 10 12 14 Mixing Ratio (ppmv) Pressure (hPa) 1 Frostpoint vs balloon remote sensing

15. CFH vs ACE-FTS

16. CFH vs MLS

17. CFH vs FISH

18. CFH vs WB-57 instruments JPL TDL

19. CFH vs. FLASH TC4 Costa Rica August 2007

20. CFH vs. FLASH AMMA/Ticosonde Veranillo: Niger vs Costa Rica August 2006

21. CFH vs WB-57 instruments Harvard Lyman alpha

22. CFH must be considered an absolute reference instrument

23. Measurement issue: In (liquid) clouds

24. Measurement in clouds

25. Wet bias with liquid phase?

26. Comparison with groundbased GPS PWV

28. Condensate phase Liquid : Coarse frost: Fine frost:

29. Logistical issues: World wide coverage

30. CFH Observation sites (campaign based)

31. Instrument availability Instrument needs (low estimate): 6 sites (2 tropical, 2 mid latitude, 2 polar) 2x per month  144 soundings per year  Industrial manufacturing

32. Instrument availability BUT conflict of Business interests ProfitProfit Trade secretsTrade secrets Science interests Economical observationsEconomical observations Understanding of instrumentUnderstanding of instrument Open access policyOpen access policy

33. Discussion points CFH observations provide highest level of confidenceCFH observations provide highest level of confidence Improve confidence in observations by cross checks of observations (ground and balloon based, satellites, aircraft)Improve confidence in observations by cross checks of observations (ground and balloon based, satellites, aircraft) Science issues to be addressed need large number of soundingsScience issues to be addressed need large number of soundings Need to address industrial production issue, involvement of radiosonde manufacturersNeed to address industrial production issue, involvement of radiosonde manufacturers