Validation of Winds Measured by MU Radar with GPS Radiosondes during the MUTSI Campaign

Abstract

For many years, mesosphere?stratosphere?troposphere (MST) radar techniques have been used for studying the structure and dynamics of the lower and middle atmosphere. In particular, these instruments are unique tools for continuously monitoring vertical and horizontal components of the atmospheric wind at high spatial and temporal resolutions. From the very beginning, many studies have been carried out analyzing the reliability of the MST radar wind measurements and their accuracy. However, until now, very few studies have been presented confirming the high performances of the VHF Middle and upper Atmospheric (MU) radar of Japan (35°N, 136°E) for measuring the wind field. The present paper thus gives original comparisons between horizontal velocities measured by MU radar and by instrumented balloons using global positioning system (GPS) radiosondes. Twelve radiosondes were successfully used during the French?Japanese MU Radar Temperature Sheets and Interferometry (MUTSI) campaign (10?26 May 2000, Japan). They were launched about 30 km westward from the radar site, hung below capesphere-type balloons. During the campaign, two sets of radar parameters with oblique beams directed 10° and 15° off zenith at 150-m and ?2-min resolutions were used. For both configurations, a very good agreement between the two kinds of measurements was found, indicating that both wind profiles are not affected by systematic measurement biases. Moreover, the standard deviation of the differences is less than 2.6 m s?1 using all radar data within a range height of 2?20 km and less than 1.5 m s?1 for a radar signal-to-noise ratio larger than 0 dB in oblique directions and a horizontal radar-balloon distance smaller than 50 km. Two cases of significant differences (10?15 m s?1) around the jet-stream altitude could qualitatively be explained by spatial and temporal variability of the wind field during the passage of a warm front.