Intraseasonal Kelvin waves along the southern coast of Sumatra and Java

The intraseasonal sea level variations along the southern coast of Sumatra and Java are investigated using in situ data and the TOPEX/Poseidon satellite altimetry data. The analysis shows that there are two intraseasonal variations of distinct timescale: 20–40 days during boreal summer (JJA) and 60–90 days during boreal winter (DJF). During boreal summer the shorter time variations of the sea level along the coast of Sumatra and Java are traced back to the eastern equatorial Indian Ocean (EIO); this indicates the importance of the remotely forced equatorial Kelvin waves. During boreal winter, on the other hand, both the remote winds over the EIO and the local alongshore winds are important in explaining the longer time variations of the sea level along the coast. Further analysis indicates that these intraseasonal variations are associated with the coastal Kelvin waves with phase speed ranging from 1.5 to 2.86 m/s. A simple analytical model forced by daily wind stress confirms the above intraseasonal variations along the southern coast of Sumatra and Java.