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Comparison Between Radar and Automatic Weather Station Refractivity Variability

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Abstract

Weather radars measure changes in the refractive index of air in the atmospheric boundary layer. The technique uses the phase of signals from ground targets located around the radar to provide information on atmospheric refractivity related to meteorological quantities such as temperature, pressure and humidity. The approach has been successfully implemented during several field campaigns using operational S-band radars in Canada, UK, USA and France. In order to better characterize the origins of errors, a recent study has simulated temporal variations of refractivity based on Automatic Weather Station (AWS) measurements. This reveals a stronger variability of the refractivity during the summer and in the afternoon when the refractivity is the most sensitive to humidity, probably because of turbulence close to the ground. This raises the possibility of retrieving information on the turbulent state of the atmosphere from the variability in radar refractivity. An analysis based on a 1-year dataset from the operational C-band radar at Trappes (near Paris, France) and AWS refractivity variability measurements was used to measure those temporal and spatial variabilities. Particularly during summer, a negative bias increasing with range is observed between radar and AWS estimations, and is well explained by a model based on Taylor’s hypotheses. The results demonstrate the possibility of establishing, depending on season, a quantitative and qualitative link between radar and AWS refractivity variability that reflects low-level coherent turbulent structures.

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Notes

  1. For practical work the equation: \(N=77.6\frac{p}{T}-5.6\frac{e}{T}+3.75\times 10^5 \frac{e}{T^2}\) (Bean and Dutton 1968) can be simplified to the two-term expression, which yields values of N within 0.02 % of those obtained with the three-term expression in the temperature range of \(-50\) to 40\(^{\circ }\hbox {C}\).

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Authors and Affiliations

  1. LATMOS/IPSL, UVSQ Université Paris-Saclay, UPMC Univ. Paris 06, CNRS, Guyancourt, France

    Ruben Hallali & Francis Dalaudier

  2. CNRM, UMR 3589, Météo-France/CNRS, Toulouse, France

    Ruben Hallali & Jacques Parent du Chatelet

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  1. Ruben Hallali
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  2. Francis Dalaudier
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  3. Jacques Parent du Chatelet
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Correspondence to Ruben Hallali.

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Hallali, R., Dalaudier, F. & Parent du Chatelet, J. Comparison Between Radar and Automatic Weather Station Refractivity Variability. Boundary-Layer Meteorol 160, 299–317 (2016). https://doi.org/10.1007/s10546-016-0145-x

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