Calibration of an Airborne Lyman-Alpha Hygrometer and Measurement of Water Vapor Flux Using a Thermoelectric Hygrometer

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  • 1 Department of Mechanical Engineering, University of California, Irvine, CA 92717
  • | 2 CIRES, University of Colorado/NOAA, Boulder, CO 80309
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Abstract

An improved calibration technique for an airborne Lyman-alpha hygrometer is presented. Like previous methods, it relies upon simultaneous measurement of absolute humidity determined from a slower response hygrometer. We show that a substantial improvement in the Lyman-alpha calibration is obtained by accounting for the time lag of the slower instrument.

To show our technique we use data from Lyman-alpha and thermoelectric devices on the NCAR Electra during an investigation of the nearly neutral boundary layer over the Arabian Sea as part of the WMO/ICSU Summer Monsoon Experiment. We also show that for near-neutral conditions the eddy-correlation water vapor flux can be adequately estimated using the fast response vertical velocity data from a gust probe and slower response data from the thermoelectric device, which has been properly advanced to account for the time lag.

Abstract

An improved calibration technique for an airborne Lyman-alpha hygrometer is presented. Like previous methods, it relies upon simultaneous measurement of absolute humidity determined from a slower response hygrometer. We show that a substantial improvement in the Lyman-alpha calibration is obtained by accounting for the time lag of the slower instrument.

To show our technique we use data from Lyman-alpha and thermoelectric devices on the NCAR Electra during an investigation of the nearly neutral boundary layer over the Arabian Sea as part of the WMO/ICSU Summer Monsoon Experiment. We also show that for near-neutral conditions the eddy-correlation water vapor flux can be adequately estimated using the fast response vertical velocity data from a gust probe and slower response data from the thermoelectric device, which has been properly advanced to account for the time lag.

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