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Proceedings with Extended Abstracts (single PDF file) - Radio ...

Proceedings with Extended Abstracts (single PDF file) - Radio ...

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SIMULTANEOUS OBSERVATIONS OFATMOSPHERIC TURBULENCE IN THE LOWERSTRATOSPHERE FROM BALLOON SOUNDINGSAND ST RADAR MEASUREMENTSR. Wilson, F. DalaudierService d’Aéronomie/IPSL1 IntroductionA field campaign combining in-situ and radar measurements, both <strong>with</strong> very high resolution,was conducted during April 1998 in St Santin (south of France). The objectives of this campaignwere:• to validate the radar calibration;• to better understand the “transfer function” of both measurement systems• to characterise the small scale turbulence from simultaneous and independent in-situ andradar observations.2 The data set2.1 The PROUST radarThe PROUST ST radar was a UHF (961 MHz) pulsed Doppler radar allowing very high resolutionmeasurements (Petitdidier et al., 1985; Delage et al., 1996; Dole et al., 2001). The rangeresolution is 30 m, integration time being reduced to 51 s. The beam width is ∼ 0.3 ◦ in the E-Wdirection and 1.1 ◦ in the N-S direction (the stratosphere is in the near field of the antenna). Thelarge Cassegrain antenna (2000 m 2 ) is pointing in the vertical direction only.2.2 The SFT measurementsSeven instrumented balloons were launched from a nearby site, about 30 km East of the radarsite. Every gondola carried a Väisälä RS80G sonde (including a GPS transponder). Threeof the gondolas, referred as SFT (“Structure Fine de Température”) carried high resolutiontemperature and pressure sensors (developed by Service d’Aéronomie). The temperature andpressure pro<strong>file</strong>s have a vertical resolution better than 20 cm. The rms noise of the temperaturedata is ∼ 5 mK rms, slightly varying <strong>with</strong> height.2.3 Inference of turbulence parametersBoth instruments provide informations on the small scale temperature fluctuations:• The radar reflectivity is related to C 2 n, the structure constant of refractive index, by assumingthat the fluctuations are induced by inertial turbulence (isotropic and homogeneous).204

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