Pergamon zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Adv. Spacr Res. Vol. 24, No. I I, pp. 15Yl-1600, 1999 0 1999 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Greal Britain www.eIsevier.nl/locate/asr PII: so273 I 177(99)00884-4 027% I 177199 $20.00 + 0.00 zyxwvutsrqp OBSERVATIONS OF ATMOSPHERIC WAVES IN THE TROPICAL PACIFIC WITH RADARS AND RADIOSONDES T. Tsudal), K. Ohnishi’), S. Yoshida’), A. Shimizul), T. Nakamura’), R. A. Vincent*), I. M. Reid*), A. Nuryanto3), H. Wiryosumarto3), S.-W. B. Harijono4), and T. Sribimawati4) zyxwvutsrqponmlkjihgfedcbaZY ‘1 Radio Atmosp h e ric Science Center (RASC), Kyoto University, Uji, Kyoto 611-0011, JAPAN *) Department of hys P its and Mathematics, University of Adelaide, A delaide 5005, Australia 3, Indonesian National Institute of Aeronautics and Space (LAPAN), Jl. Pemuda Persil No.1, Jakarta Timur 13220, INDONESIA 4, Agency for the Assessment and Application of Technology (BPPT), Jl. M. H. Thamrin No.8, Jakarta 1034 0, INDONESIA zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ABSTRACT By an international research consortium between Japan, Indonesia and Australia, we have been operating a meteor wind radar (MWR) near Jakarta (6.4”S, 106.7”E) since November 1992, and a medium frequency (MF) radar in Pontianak (O.O3”N,109.3”E), west Kalimantan, from November 1995, respectively. We also conducted campaign observations with a balloon-borne radiosonde in LAPAN observatories in Watukosek (7.6”S, 112.7”E), Bandung (6.9”S, 107.6”E) and Pontianak since February 1990. In this paper, radar observations of wind fields in the mesosphere and lower thermosphere (MLT) region are used to study equatorial atmosphere dynamics. We first describe the long-term behavior of zonal wind at 70-100 km using the Jakarta MWR data during November 1992 and October 1997. The mesospheric semiannual oscillation (MSAO) is dominant in the equatorial MLT region, whose westward winds were much larger in March-April than in September-October. Moreover, the maximum amplitudes of MSAO showed a clear biennial periodicity. We also discuss characteristics of ultra-fast Kelvin (UFK) waves, having wave period of 3-4 days. A correlative study between the Jakarta MWR and MF radars at Pontianak and Christmas Island (2”N, 158’W) has indicated that the UFK wave propagates eastward at a zonal wavenumber one. We have further analyzed the long-term behavior of the UFK waves in Jakarta, and have found that the wave activity is characterized by strong enhancements twice a year, having a large value in the westward winds of MSAO. Ol’)OO COSPAR. Published by Elsevier Science Ltd. OBSERVATIONS IN EQUATORIAL INDONESIA It has now become commonly recognized that convection and various atmospheric waves in equato- rial regions play an important role in maintaining the global atmospheric circulation of the middle atmosphere. Extensive observations of the equatorial atmosphere have been carried out in the last decades by means of a balloon or rocket-borne equipment as well as ground-based radars. Although most of the coordinated radar studies were carried out at middle and high latitudes, new radar sites have recently been established at low latitudes, for example, MF radars in Christmas Island [Vincent and Lesicar, 19911 and Kauai, Hawaii (22”N, 16pW) [n-itts and Isler, 19921. Since November 1992 we have been operating MWR in an observatory in the Indonesian National Center for Research, Science and Technology (PUSPIPTEK) (6.4”S, 106.7”E), located about 27 km 1591