Annual Rossby wave in the southern Indian Ocean: Why does it "appear" to break down in the middle ocean?

Using both altimetry data (TOPEX/Poseidon and Geosat) and Levitus climatolo gy and a linear reduced-gravity model, the authors studied the annual Rossb y waves in the southern Indian Ocean from 19 degrees to 9 degreesS. The mos t striking feature from the data analysis is that the westward phase propag ation of the annual variability appears to break up in the midocean, which results in two local maxima for annual variability in both the sea level an d the depth of the 18 degreesC isotherm, with one in the eastern basin and the other in the western basin. Separating the two maxima is a midocean min imum. Decomposition of the annual variability into Rossby waves and localiz ed response indicates that the two local maxima of the annual variability s imply result from the constructive interference between the localized respo nse and the Rossby waves in the eastern and western basin. On the other han d, the midocean local minimum results from the destructive interference bet ween the Rossby waves and the localized response. Modeling results suggest that the bulk of the annual variability in the study domain is driven by wi nd forcing, while forcing by throughflow through eastern boundary radiation is of minor importance. Dissipation is found to have a much greater impact on the Rossby waves than on the local response.