Cross-equatorial structures of equatorially trapped nonlinear Rossby waves |
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| Institution: | 1. Soil Science, University of Rostock, Justus-von-Liebig-Weg 6, 18051 Rostock, Germany;2. Institute of Biology and Environmental Sciences (IBU), Department of Soil Science, Carl von Ossietzky University of Oldenburg, D-26111 Oldenburg, Germany;3. Department of Geosciences, Research Area Geography, Laboratory of Soil Science and Geoecology, Eberhard Karls University of Tübingen, Rümelinstr. 19–23, 72070 Tübingen, Germany;4. NIBIO – Norwegian Institute of Bioeconomy Research; Department of Landscape Monitoring, PO Box 115, 1431 Ås, Norway;5. Department of Geography, University of Bergen, PO Box 7802, 5020 Bergen, Norway;6. Canadian Light Source Inc., Saskatoon, Saskatchewan S7N 5A8, Canada |
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| Abstract: | Analysis of the Sea Surface Height (SSH) from satellite altimeters has shown that equatorially trapped Rossby waves exhibit asymmetric cross-equatorial structures; their northern extrema are much larger in magnitude than their southern counterparts. Such asymmetry is inconsistent with the classical theory for the first baroclinic, first meridional equatorially trapped Rossby mode, which predicts that SSH and zonal velocity are symmetric in latitude and the meridional velocity is latitudinally antisymmetric (Matsuno, 1966). Chelton et al. (2003) attributed the observed asymmetry to the mean-shear-induced modifications of first meridional mode Rossby waves. The present paper examines nonlinear rectification of cross-equatorial wave structures in the presence of different zonal mean currents. Nonlinear traveling Rossby waves embedded in shears are calculated numerically in a 1.5-layer model. Nonlinearity is shown to increase the cross-equatorial asymmetry substantially making the northern extrema even more pronounced. However, nonlinearity only slightly increases the magnitude of the westward phase speed. |
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| Keywords: | Equatorially trapped Rossby wave Asymmetric cross-equatorial structure Nonlinear effect |
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