The 2 - 16 day recurrence cycle of daily sporadic-E activity and its relation to planetary-wave activity observed with MF radar in spring and summer 1996 |
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| Affiliation: | 1. Dipartimento di Fisica, Università di Roma “La Sapienza”, 00185 Rome, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia, 00143 Rome, Italy;1. Institute for Meteorology, University of Leipzig, Stephanstr. 3, D-04103 Leipzig, Germany;2. Institute for Geology and Geophysics, University of Leipzig, Collm Observatory, D-04758 Collm, Germany;1. National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 Japan;2. Academia Sinica Institute of Astronomy & Astrophysics, PO Box 1-87, Nankang, Taipei 115 Taiwan;3. Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 Japan;1. Radio Atmospheric Science Center, Kyoto University, Uji, Kyoto 611-0011, Japan;2. Faculty of Engineering, Shinshu University, Nagano, Japan;3. Graduate School of Electrical Engineering, Tokyo Metropolitan University, Tokyo, Japan;4. National Research of Polar Research, Tokyo, Japan;1. Atmospheric Physics Laboratory, University College London 67-73 Riding House Street, London W1P 7PP, UK;2. CIRES, Univ. of Colorado and NOAA Space Environment Laboratory 325 Broadway, Boulder, CO 80303, USA |
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| Abstract: | We observed daily sporadic-E activity in Japan using a series of ionosondes and discovered that the activity occurred in recurrent cycles, lasting approximately 2 to 16 days. We describe the cycles by referring to scaled data recorded in 15-minute segments during 1996. Planetary-wave activity in the lower thermosphere was observed during the same period with an MF radar located at Yamagawa (31.2° N, 130.6° E) in western Japan. We discuss the recurrent phenomenon in spring and summer 1996, sporadic-E exceeds 5 MHz in critical frequency, in relation to the periods of wind oscillations derived from MF-radar wind observations. From April to May 1996, there was a period of increased sporadic-E activity. The periods in which the occurrence rate of foEs exceeded 5 MHz in critical frequency decreased gradually from 7.4 to 5 days and correspond to long-period oscillations of meridional winds tracked by the MF radar at Yamagawa. In August 1996, we found the spectra of foEs observed at Yamagawa occurred in periods of 1.6, 2, 8, and 16 days. Our results strongly support the possibility that planetary waves play a significant role in generating long periods of oscillations in foEs. |
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