INERTIO-GRAVITY WAVES AND SUBTROPICAL MULTIPLE TROPOPAUSES - VERTICALWAVE-NUMBER SPECTRA OF WIND AND TEMPERATURE OBSERVED BY THE MU-RADAR,RADIOSONDES AND OPERATIONAL RAWINSONDE NETWORK

We have carried out continuous observations of the tropopause region o ver Japan for three weeks during the Baiu (early summer rain ''in Japa n'') season in 1991, by using a VHF Doppler radar (the MU radar), radi osondes launched at the radar site and operational rawinsondes at five meteorological stations. Based on these observations, we try to exami ne the hypothesis that the multiple tropopauses and the dominant inert io-gravity waves are one and the same feature, and obtain some interes ting results that are not inconsistent with this hypothesis. First, ve rtical wavenumber spectra and hodographs analyzed from the radar wind data in the tropopause region suggest that inertio-gravity waves with vertical wavelengths of similar to 2 km are quasi-monochromatically do minant (with 2-3 day scale variabilities of 10-20%), and are in accord ance with activities of the subtropical jet stream and mesoscale cyclo ne-front system activities observed by the operational network. Second , striking (potential) temperature fluctuations are detected simultane ously by the radiosondes and rawinsondes, which appear as multiple tro popauses in meridional cross-section analysis. Third, vertical wavenum ber spectra analyzed from the radiosonde temperature data are consiste nt with the radar wind spectrum, if we assume that both wind and tempe rature fluctuations are mainly induced by the dominant inertio-gravity waves. Finally, we confirm that the dominant inertio-gravity waves ca n be barely detected also from routine rawinsonde (1.5-km running-mean ) wind data if the amplitude is larger than 1.5 m/s. However, the mono chromatic wave structures are generally quite localized in space and t ime.