1. AIRS science team meeting, Greenbelt, 31 March 2003 Holger Vömel University of Colorado and NOAA/CMDL Cryogenic Frost point Hygrometer (CFH) Measurements during AWEX and previous RS90 comparisons

2. Overview The University of Colorado Cryogenic Frost point Hygrometer (CU-CFH) Accuracies SnowWhite comparison with CFH RS90 comparisons with NOAA/CMDL hygrometer

3. CU-CFH Sonde Weight: ~ 500 gr Microprocessor controlled Digital interface with ECC Easy to use and robust Continuous measurements between surface and 28 km

4. Night launch, Oklahoma

5. Accuracy Measurement uncertainty of frostpoint temperature (AWEX)<.5K (2 σ) Air temperature measurement <.2K  Uncertainty in RH< 4…8% of RH value depending on altitude and uncertainty in air temperature Uncertainty in TPW < 5% Use WMO formulas to calculate vapor pressures (similar to Hyland and Wexler, which Vaisala uses)

6. CFH sounding Oklahoma MR

7. Mean comparison to Snow White vs CFH, Oklahoma

9. RS90 comparisons with NOAA/CMDL hygrometer

11. Take home message CFH measures on the 5% accuracy level. Snow White has no bias issue, but some performance limitations RS90 may have a slight dry bias 5-10% possibly due to contamination

13. Snow White upper tropospheric limit Upper tropospheric limit depends on frost-point temperature At T FP < -75°C the Snow White does no longer measure reliably

14. Snow White upper tropospheric limit Upper tropospheric limit depends on frost-point temperature At T FP < -75°C the Snow White does no longer measure reliably