Cooperative studies on dynamic interactions of tides -atmospheric tides in the lower thermosphere-

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In this project, the coupling process of the middle and upper atmosphere due to atmospheric tides and associated waves is studied, by means of ground based radar technique. The observations with the lidars and radiosondes are also utilized to investigate the generation and propagation process of these waves. The major part of this study is the comparison of the radar observations with the middle and upper atmosphere radar (MU radar)in Kyoto, Japan, Adelaide MF radar in Australia and Saskatoon MF radar in Canada. Those three radar are operated regularly and with good height and time resolutions.First of all we discussed the effect of the difference of radar techniques among these three radars to the results obtained by the analysis, and developed the most useful way of the analysis for the quantitative study. Next we compared the huge database obtained with these three radars, and found that the gravity wave energy is almost same magnitude between the northern and southern hemisphere but smaller in the higher latitude. This fact contradicts to the present interpretation of the tidal observations which requires a stronger gravity wave activity in the northern hemisphere to induce a large hemispheric difference of tides, and showed the necessity of further study with more observations in future.We also carried out the simultaneous observation with these three radars for several times and found a strong activity of quasi-two day waves. However, our cooperative study has shown that the energy of the planetary waves other than two-day components are much smaller. The study of lower atmospheres indicated that the possibility of the tidal generations at the low latitude regions.In summary, we have improved our understanding of tides and associated waves in the lower thermosphere and their coupling processes by using radars and other facilities among Australia, Canada and Japan, and the observations including equatorial regions are found to be very important in future.