Validation of winds measured by MU radar with GPS radiosondes during the MUTSI campaign

For many years, mesosphere-stratosphere-troposphere (MST) radar techniques have been used for studying the structure and dynamics of the lower and mid dle atmosphere. In particular, these instruments are unique tools for conti nuously monitoring vertical and horizontal components of the atmospheric wi nd at high spatial and temporal resolutions. From the very beginning, many studies have been carried out analyzing the reliability of the MST radar wi nd measurements and their accuracy. However, until now, very few studies ha ve been presented confirming the high performances of the VHF Middle and up per Atmospheric (MU) radar of Japan (35 degreesN, 136 degreesE) for measuri ng the wind field. The present paper thus gives original comparisons betwee n horizontal velocities measured by MU radar and by instrumented balloons u sing global positioning system (GPS) radiosondes. Twelve radiosondes were s uccessfully used during the French-Japanese MU Radar Temperature Sheets and Interferometry (MUTSI) campaign (10-26 May 2000, Japan). They were launche d about 30 km westward from the radar site, hung below capesphere-type ball oons. During the campaign, two sets of radar parameters with oblique beams directed 10 degrees and 15 degrees off zenith at 150-m and similar to2-min resolutions were used. For both configurations, a very good agreement betwe en the two kinds of measurements was found, indicating that both wind profi les are not affected by systematic measurement biases. Moreover, the standa rd deviation of the differences is less than 2.6 m s(-1) using all radar da ta within a range height of 2-20 km and less than 1.5 m s(-1) for a radar s ignal-tonoise ratio larger than 0 dB in oblique directions and a horizontal radar-balloon distance smaller than 50 km. Two cases of significant differ ences (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.