Decadal change in intraseasonal variability over the South China Sea

Evidence is presented to reveal a decadal change around mid-1990s in the behavior of intraseasonal variability (ISV) over the South China Sea (SCS). During 1979-1993, the ISV has a spectral peak around 64 days, which is longer than in the recent epoch of 1994-2007 (around 42 days). The ISV event in 1979-1993 involves a merging process of the northward and westward propagating convection anomalies over the western North Pacific. The ISV in 1994-2007 has no such a merging process but exhibits a tilted band structure extending from the northern Indian Ocean to the SCS, which is strongly connected to the equatorial eastward propagating Madden-Julian Oscillation. The merging process during 1979-1993 modified the ISV over the SCS, resulting in the prolonged period, enhanced convective activity and a weakened relationship with the eastward propagating MJO. The possible cause of this change is discussed