Observation of mixed Rossby-gravity waves in the Western equatorial Pacific |
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| Authors: | Xiao-Hua Zhu Arata Kaneko Noriaki Gohda Hideo Inaba Kunio Kutsuwada Marie-Helene Radenac |
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| Institution: | (1) Department of Environmental Sciences, Faculty of Engineering, Hiroshima University, 739 Higashi-Hiroshima, Japan;(2) School of Marine Science and Technology, Tokai University, 3-20-1 Orido, Shimizu, 424 Shizuoka, Japan;(3) ORSTOM-LODYC, Tour 14, case 100, place Jussieu, 05 Cedex, 75252 Paris, France |
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| Abstract: | During the IOP (Intensive Observation Period) of TOGA/COARE (Tropical Ocean and Global Atmosphere/Coupled Ocean Atmosphere
Response Experiment) from December 1992 to February 1993, four Japanese moored ADCPs (Acoustic Doppler Current Profilers)
measured vertical profiles of three-component velocities at the stations 2S (2°S, 156°E), 2N (2°N, 156°E), 154E (0°N, 154°E)
and 147E (0°N, 147°E). Power spectra of the surface current showed a pronounced peak having a period of around 14 days for
both the zonal and meridional velocities at the stations 2S and 2N near the equator, and for only the meridional velocity
at the equator. This 14-day phenomenon is considered to be a kind of equatorial wave of the first baroclinic mode, from a
comparison of the result of the vertical mode analysis and the vertical distribution of the standard deviation of band-pass
filtered velocity fluctuations. A dispersion relationship obtained from the horizontal mode analysis of this wave confirmed
that the 14-day phenomenon is a mixed Rossby-gravity wave with the westward propagating phase speed and eastward propagating
group velocity. From the cross-spectral analysis of velocity data, the average phase speed and wavelength of the wave were
estimated as 3.64 m s−1 and 3939 km, respectively, for station pair 2S∼147E. These values were in good agreement with the average phase speed and
wavelength of 3.58 m s−1 and 3836 km estimated from the dispersion curve and the observed period. A northerly wind burst blew over all the mooring
sites during the middle of the observation period. The mixed Rossby-gravity wave, which is anti-symmetric for the zonal velocity
about the equator, is likely to be forced by this northerly wind burst crossing the equator. Generation of the oceanic mixed
Rossby-gravity wave of the first baroclinic mode is discussed in association with the atmospheric Rossby wave having the same
period. |
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| Keywords: | Mixed Rossby gravity waves equatorial Pacific TOGA/COARE moored ADCPs |
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