Resonance of baroclinic waves in the tropical oceans: The Indian Ocean and the far western Pacific |
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| Institution: | 1. Department of Physics, Faculty of Science, Port Said University, Port Said 42521, Egypt;2. Research Center for Physics (RCP), Department of Physics, Faculty of Science and Arts, Al-Mikhwah, Al-Baha University, Saudi Arabia;3. Mathematics Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia;4. King Abdullah City for Atomic and Renewable Energy (K.A.CARE), Riyadh, Saudi Arabia;5. Department of Mathematics, Universidad Nacional de Colombia, FIZMAKO Research Group, Colombia |
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| Abstract: | The Indian Ocean has a particularity, its width is close to half the wavelength of a Rossby wave of biannual frequency, this coincidence having been capitalized on by several authors to give the observations a physical basis. The purpose of this article is to show that this is not the case since the resonance of tropical baroclinic waves occurs in all three oceans. This is because the westward-propagating Rossby wave is retroflexed at the western boundary to form off-equatorial Rossby waves dragged by countercurrents before receding and turning back as a Kelvin wave. Thus a quasi-stationary baroclinic wave is formed, whose mean period is tuned to the forcing period. Two independent basin modes resonantly forced are highlighted – 1) a nearly symmetric zonal 1/2-yr period Quasi-Stationary Wave (QSW) that is resonantly forced by the biannual monsoon. It is formed from first baroclinic mode equatorial-trapped Rossby and Kelvin waves and off-equatorial Rossby waves at the western antinode. This QSW controls the Equatorial Counter Current at the node. The Indian Ocean Dipole (IOD) results from a subharmonic mode locking resulting from the coupling of this QSW and the 2nd, 3rd and 4th baroclinic modes - 2) a 1-yr period QSW formed from an off-equatorial baroclinic Rossby wave, which is induced from the southernmost current of the Indonesian Throughflow through the Timor passage, propagating in the southern and northern hemispheres: the drivers are south-easterlies in the southern hemisphere and monsoon wind in the northern hemisphere. |
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| Keywords: | Resonantly forced waves Coupling of basin modes Tropical Indian Ocean Indian oscillation dipole |
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