Performance of On-line Measurements of The Global Distribution of Humidity In The Free Troposphere (0-13 Km Altitude)

Better knowledge of the water vapor distribution would enhance the reliability and evidence of prognostic model simulations of chemistry, weather and climate of the atmosphere considerably (eg. IPCC-report, 2001), particularly in the middle/upper troposphere and lower stratosphere. Only few water vapor measurements of sufficient quality in this regions of the atmosphere have been reported (Kley and Russell, 1999). The EC-programme MOZAIC has shown that in-service aircraft are an ideal platform for continuous and accurate measurements (Helten et al, 1998). In the frame of the German AFO-2000 research programme a stand alone humidity measuring system is under development, small, light weighted quasi maintenance-free on one hand and re- liable, precise, and accurate on the other, with emphasis on quality assurance of the measured data. An important aim will be to achieve on-line access of the measured data for weather services, to support meteorological synoptic and weather forecasting. Results of in-flight performance tests obtained from several flights onboard a research aircraft during SPURT campaigns, where a Lyman-alpha photofragment fluorescence hygrometer was used as a reference instrument (Zöger et al., 1999), will be presented and discussed. References: Helten, M., H. G. J. Smit, W. Sträter, D. Kley, P. Ned- elec, M. Zöger, R. Busen, Calibration and performance of automatic compact instru- mentation for the measurement of relative humidity from passenger aircraft, J. Geo- phys. Res., 103, 25,643-25,652, 1998. IPPC (=Intergovernmental Panel on Climate Change), Third Assessment Report - Climate Change 2001 : The Scientific Basis, Cambridge University Press, 2001 Kley, D., and J.R. Russell III, Plan for the SPARC Water Vapour Assessment (WAVAS), SPARC Newsletter, 13, 5-8,1999. Zöger, M., A. Afchine, N. Eicke, M.-T. Gerhards, E. Klein, D.S. McKenna, U. Mörschel, U. Schmidt, V. Tan, F Tuijter, T. Woyke, C. Schiller, Fast in situ stratospheric hygrom- eters: A new family of balloon-borne and airborne Lyman-alpha photofragment fluo- rescence hygrometers, J. Geophys. Res., 104, 1807-1816, 1999.