Sea level and circulation variability of the Gulf of Carpentaria: Influence of the Madden-Julian Oscillation and the adjacent deep ocean

The Madden-Julian Oscillation (MJO) is a significant contributing factor to intraseasonal variability in both the tropical and extratropical atmosphere and ocean. Sea level and circulation variations in the Gulf of Carpentaria (northern Australia) and the coastal regions of the northeastern Indian Ocean and eastern Pacific have been shown to be related to the MJO. A nonlinear barotropic numerical model, validated with local tide gauge data, is used to study the Gulf of Carpentaria from 1979 to 2009. It is shown that the model reproduces well the seasonal cycle of sea level as well as intraseasonal variations and their seasonal modulations. Intraseasonal variability is shown to be driven by surface wind stress that is closely related to the MJO. The model is next used to remove the local wind effect from the tide gauge data, resulting in a low-frequency residual signal. This low-frequency signal is interpreted in terms of larger-scale modes of variability of the adjacent shelf seas and the Indian and Pacific oceans through comparison with climatological indices, correlations with regional sea level measured by altimeters, and Hovmoller diagrams. It is shown that this signal is generated in the Pacific and related to the El Nino-Southern Oscillation. The implications for predictability and forecasting in the Gulf of Carpentaria on intraseasonal timescales are discussed.