Propagation characteristic and intraseasonal oscillation of the swell energy of the Indian Ocean

The propagation characteristics of swell energy are important for applications such as swell wave power generation, ocean wave forecasting, disaster prevention and reduction, etc. However, the study on the propagation of swell energy is still relatively rare. This study proposed a new method to exhibit the exact propagation route and speed and intraseasonal oscillation of swell energy. The Indian Ocean is selected as a case study, using the 45-year (1957.09-2002.08) European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA-40) wave reanalysis dataset. The main results are as follows. (1) empirical orthogonal function (EOF) analysis and 6-hourly zonal averages of swell wave power density (WPD) show that the Indian Ocean swell energy has an obvious but fluctuating northeastward propagation. (2) The swell energy of the southwest Indian Ocean generally spreads to two regions: the main body propagates in a NE-NNE direction to Sri Lankan waters, while a small branch propagates to Christmas Island waters. (3) Swell energy in the west of the southern Indian Ocean westerly (SIOW), in Sri Lankan waters, and in Christmas Island waters share a common period of quasi-weekly oscillation. Swell energy takes ∼6 days to propagate from the west of the SIOW to Sri Lankan and Christmas Island waters. Swell energy propagates faster during June-September than in other months.