A New Shipborne Microwave Refractometer for Estimating the Evaporation Flux at the Sea Surface

J.-Y. Delahaye CETP (CNRS), Velizy, France

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C. Guerin CETP (CNRS), Velizy, France

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J. P. Vinson CETP (CNRS), Velizy, France

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H. Dupuis DGO (CNRS), Bordeaux, France

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A. Weill CETP (CNRS), Velizy, France

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H. Branger IRPHE (CNRS), Parc Scientifique et Technologique de Luminy, Marseille, France

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L. Eymard CETP (CNRS), Velizy, France

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J. Lavergnat CETP (CNRS), Velizy, France

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G. Lachaud CNRM/Meteo France, Toulouse, France

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Abstract

After a brief description of humidity measurement and a short presentation of methods of microwave refractometry for evaporation flux, a new X-band refractometer system is presented. Based on a new design and a new material for the microwave cavity, it does not need calibration for refractive index variations because of its reduced thermal time constant.

The new device has been combined with a sonic anemometer and traditional mean meteorological measurements on a 12-m shipborne mast. It has been found to be very efficient for obtaining humidity fluctuations and fluxes in the CATCH 97 (Couplage avec l’ATmosphère en Conditions Hivernales) and FETCH 98 (Flux, Etat de la mer et Télédétection en condition de fetCH variable) experiments under various wind and stability conditions. The inertial subrange is of very high quality. To first order, the evaporation flux and refractive index flux are very similar. In extreme meteorological conditions, such as those encountered during CATCH, the sensible heat flux contribution must be determined independently.

A great advantage of the system is that the contamination by salt, as is typical for other devices at sea, has been found to be negligible for the conditions encountered.

Corresponding author address: Dr. Jean-Yves Delahaye, Centre d’études des Environnements Terrestre et Planétaires, 10/12 avenue de l’Europe, 78140 Vélizy, France.

Email: delahaye@cetp.ipsl.fr

Abstract

After a brief description of humidity measurement and a short presentation of methods of microwave refractometry for evaporation flux, a new X-band refractometer system is presented. Based on a new design and a new material for the microwave cavity, it does not need calibration for refractive index variations because of its reduced thermal time constant.

The new device has been combined with a sonic anemometer and traditional mean meteorological measurements on a 12-m shipborne mast. It has been found to be very efficient for obtaining humidity fluctuations and fluxes in the CATCH 97 (Couplage avec l’ATmosphère en Conditions Hivernales) and FETCH 98 (Flux, Etat de la mer et Télédétection en condition de fetCH variable) experiments under various wind and stability conditions. The inertial subrange is of very high quality. To first order, the evaporation flux and refractive index flux are very similar. In extreme meteorological conditions, such as those encountered during CATCH, the sensible heat flux contribution must be determined independently.

A great advantage of the system is that the contamination by salt, as is typical for other devices at sea, has been found to be negligible for the conditions encountered.

Corresponding author address: Dr. Jean-Yves Delahaye, Centre d’études des Environnements Terrestre et Planétaires, 10/12 avenue de l’Europe, 78140 Vélizy, France.

Email: delahaye@cetp.ipsl.fr

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