HR: 11:05h
AN: G31C-04    [PDF]
TI: Ocean Bottom Pressure Measurements Off Sanriku, Japan
AU: * Sato, T
EM: tsato@miz.nao.ac.jp
AF: National Astronomical Observatory, Mizusawa, 2-12 Hoshigaoka, Mizusawa, 023-0861 Japan
AU: Fujimoto, H
EM: fujimoto@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Matsumoto, K
EM: matumoto@miz.nao.ac.jp
AF: National Astronomical Observatory, Mizusawa, 2-12 Hoshigaoka, Mizusawa, 023-0861 Japan
AU: Tamura, Y
EM: tamura@miz.nao.ac.jp
AF: National Astronomical Observatory, Mizusawa, 2-12 Hoshigaoka, Mizusawa, 023-0861 Japan
AU: Higashi, T
EM: higashi@kugi.kyoto-u.ac.jp
AF: Graduate School of Science, Kyoto University, Oiwakecho, Kitashirakawa, Sakyoku, Kyoto, 606-8502 Japan
AU: Nishino, M
EM: nishino@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Hino, R
EM: hino@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Kanazawa, T
EM: kanazawa@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: Variable motions of the ocean are changing the Earth's gravity field. For example, mass exchange in the Pacific Ocean is considered to be the most probable source of the recent rapid and large change in the J2 term, which may be related to the ENSO event in 1997 (Cox and Chao, 2002). The actual ocean mass exchange related to that event was also observed from ocean bottom pressure records (OBPRs) offshore of Peru (Fujimoto et al., 2003). On the other hand, satellite altimetry measurements, such as TOPEX/Poseidon (T/P), enable us to estimate the oceanic effect on gravity observations using globally-gridded data for sea surface height (SSH) variability. However, the altimeter data are affected by steric changes in the ocean, which should not contribute to the observed gravity changes (for example, Sato et al., 2001). In order to examine the relation among the mass exchange in the oceans, SSH variation, and gravity changes, we began a three-year observation project in 2001 to measure the ocean bottom pressure changes at the three crossover points of the T/P satellite off Sanriku, Japan: 143.1E, 39.2N (Point-A); 146.0E, 39.2N (Point-B); and 144.6E, 41.5N (Point-N). The data are sampled at an interval of one minute. Here, we will report the analysis results for the OBPR data for the two years since the beginning of the observations. Although the records at Point-N show a peculiar time variation, we obtained clear tidal signals at Point-A and Point-B. We compared the tidal analysis results with a global ocean tide model, NAO99b (Matsumoto et al., 2000), and we confirmed that, at both Point-A and Point-B, the predicted tides agree to the actual observations within the difference of 1 % in amplitude for the four major tidal waves: M2, S2, K1 and O1. This suggests that it may be possible to correct the tidal effect on the satellite gravity data with an accuracy of about 1 % by using recent global tide models. We also compared residuals of the OBPR data, which were obtained by subtracting the tides and long-term trend, with the T/P data. Two corrections were applied to the T/P data: one for the tide and one for the inverted barometer (IB) response of the ocean to air pressure changes. We found that at Point-B (about 350 km from the nearest coast) the corrected T/P data show temporal variations well correlated with the pressure observations. However, at Point-A (about 110 km from the coast), no meaningful correlation is observed. Our results suggest the possibility that the SSH variations observed from T/P may exhibit the barotropic component in the open ocean distant from coastal regions where western boundary currents are dominant. For the two-year observations at Point-B, the barotropic signals have a magnitude of about 7 cm in the peak-to-peak amplitude and show four dominant peaks at periods of 205, 128, 50, and 28 days.
DE: 0350 Pressure, density, and temperature
DE: 1200 GEODESY AND GRAVITY
DE: 6062 Satellites
DE: 9355 Pacific Ocean
SC: Geodesy [G]
MN: 2003 Fall Meeting