Solutions for Improving the Radar Refractivity Measurement by Taking Operational Constraints into Account

Lucas Besson Météo France, DSO/CMI, LATMOS/IPSL, Guyancourt, France

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Jacques Parent du Châtelet Météo France, DSO/CMI, LATMOS/IPSL, Guyancourt, France

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Abstract

Atmospheric refractivity depends on meteorological parameters such as temperature, water vapor pressure, and air pressure and can be measured using weather radar. This could be useful for convection prediction through the assimilation by numerical forecasting models in the boundary layer, particularly in prestorm conditions. However, this measurement is highly sensitive to phase ambiguities, induced by signal undersampling during rapid atmospheric fluctuations because of strong turbulent fluxes in the boundary layer or during extreme events. The refractivity measurement has been recently implemented on some radars of the French Application Radar à la Météorologie Infra-Synoptique (ARAMIS) network, which is composed of three different frequencies (S, C, and X bands). In view of operational applications, investigations are performed to improve the measurement and limit the phase ambiguity rate. The first recommendation is to decrease the time interval between two measurements by increasing the antenna speed rotation or by the use of a higher elevation angle. These methods lead to decreased sensitivity of the refractivity to the phase aliasing. The second recommendation is to improve the information from ground target by combining the two polarization radar returns and using shorter pulse width. These two different approaches, based on the radar capacity and the description of the target, are complementary and noticeably improve the quality of the refractivity retrieval.

Corresponding author address: Lucas Besson, Météo France, DSO/CMI, LATMOS/IPSL, 11 bd D'Alembert, 78280 Guyancourt, France. E-mail: lucas.besson@latmos.ipsl.fr

Abstract

Atmospheric refractivity depends on meteorological parameters such as temperature, water vapor pressure, and air pressure and can be measured using weather radar. This could be useful for convection prediction through the assimilation by numerical forecasting models in the boundary layer, particularly in prestorm conditions. However, this measurement is highly sensitive to phase ambiguities, induced by signal undersampling during rapid atmospheric fluctuations because of strong turbulent fluxes in the boundary layer or during extreme events. The refractivity measurement has been recently implemented on some radars of the French Application Radar à la Météorologie Infra-Synoptique (ARAMIS) network, which is composed of three different frequencies (S, C, and X bands). In view of operational applications, investigations are performed to improve the measurement and limit the phase ambiguity rate. The first recommendation is to decrease the time interval between two measurements by increasing the antenna speed rotation or by the use of a higher elevation angle. These methods lead to decreased sensitivity of the refractivity to the phase aliasing. The second recommendation is to improve the information from ground target by combining the two polarization radar returns and using shorter pulse width. These two different approaches, based on the radar capacity and the description of the target, are complementary and noticeably improve the quality of the refractivity retrieval.

Corresponding author address: Lucas Besson, Météo France, DSO/CMI, LATMOS/IPSL, 11 bd D'Alembert, 78280 Guyancourt, France. E-mail: lucas.besson@latmos.ipsl.fr
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