Discovery of the Significant Impacts of Swell Propagation on Global Wave Climate Change

This study compared the differences in the wave climate in the South China Sea and North Indian Ocean under these two datasets: ERA-40 wave reanalysis and Mei’s hindcast wave data. In the numerical calculation of regional ocean waves, the wave climate characteristics exhibited significant bias if the influence of external swells (swells from afar) was not fully considered, which may provide an incorrect basis for global climate change analysis. 1) The trends of the significant wave height (SWH) obtained from the two datasets showed significant differences, such as those of the Bay of Bengal and the Java Sea in June–July–August. For the past 45 years, SWH from ERA-40 (SWH-ERA) exhibited a significant annual increase in low-latitude waters of the North Indian Ocean (0.2–0.6 cm yr−1) and South China Sea (0.2–0.8 cm yr−1). 2) In the Bay of Bengal, the SWH-ERA in each month was generally 0.5 m higher than the SWH from Mei’s hindcast wave data (SWH-Mei) and can reach 1.0 m higher in some months. 3) In the Bay of Bengal, SWH-ERA and SWH-Mei increased significantly at annual rates of 0.13 and 0.27 cm yr−1, respectively. This increasing trend was mainly reflected after 1978. SWH-ERA showed a trough in 1975 (1.33 m) and a crest in 1992 (1.83 m), which were not reflected in SWH-Mei.