CIRES/ESRL Scientists at the Center of Large Scale Water Vapor Intercomparison
Global Monitoring Division - ESRL-GMD
Twenty four instruments from 17 research groups located in 7 countries joined in an international effort called Aqua Validation and Instrument Tests (AquaVIT) to resolve discrepancies in atmospheric water vapor measurements. This research effort was hosted at the aerosol chamber facility AIDA of the Research Center Karlsruhe, Germany. The experimental phase took place from 6 to 26 October 2007 and data are currently being analyzed and submitted to independent referees of the Research Center and NOAA ESRL. A key instrument in this intercomparison is the Cryogenic Frostpoint Hygrometer (CFH), which is built at the Cooperative Institute for Research in Environmental Sciences of the University of Colorado with NOAA support.

Background: Water vapor measurements in the upper troposphere and lower stratosphere have consistently shown discrepancies between different instruments despite careful calibration and testing of these instruments. The CFH is currently being used as reference instrument in the validation of satellite instruments, radiosondes, lidar systems and UAS based detectors. Large discrepancies exist in direct comparisons between measurements by the NASA high altitude research aircraft WB-57F and those by the CFH. Inconsistencies have also been found in the comparison of other instruments in this altitude region, which have not yet been resolved.

Significance: Atmospheric water vapor is a key greenhouse gas. In a changing climate it is expected to show the strongest feedback signal in the upper troposphere and possibly the lower stratosphere. Monitoring water vapor in this altitude region and understanding the physical processes that control the distribution of water vapor and the formation of cirrus clouds is of highest importance. The validity of some of these measurements and resolving the discrepancies, which have persisted for decades, will influence how atmospheric water vapor is treated in numerical computer models of the atmosphere and will improve our ability to predict future climate changes.

More information:

Contact information
Name: Holger Voemel
Tel: (303) 497-6192