The Characteristics of Intraseasonal Oscillation Intensity

The characteristics of intraseasonal oscillation (ISO) intensity based on Outgoing Longwave Radiation (OLR) and sea surface temperature (SST) measurements have been investigated in this paper. Results show two strong OLR ISO centers located in the tropical Indian Ocean and thetropical western Pacific warm pool region, where their averaged SST are higher than over other areas. The intensity of the OLR ISO in the boreal winter and spring is stronger than that in the boreal summer and autumn. The southward/northward propagation of these centers has a feature of seasonal variations. The interannual variation of the OLR ISO intensity shows three most active regions, i.e., the northwest Pacific, the southwest Pacific and the tropical eastern Pacific Ocean, where are co-located with the maximum local SST anomaly. This phenomenon is especially prominent in the boreal winter and spring. The SST anomaly is also related to El Nino/La Nina events. Results provide evidences that the SST variation has an important influence on the OLR ISO intensity. Similarly, the SST ISO has three strong active centers, i.e., the tropical eastern Pacific, the northwest Pacific and the southwest Pacific Ocean, where the climatic mixing layer depth (MLD) is short. The strong ISO activity exists annually in the tropical eastern Pacific, while in the boreal and austral spring for northwest Pacific and in summer and autumn for the southwest Pacific Ocean. Results also indicate a negative relationship between the SST ISO intensity and MLD over these regions. In addition, a negative relationship between the oceanic wind at 10m and SST ISO is evident, indicating that the wind drifting and sensible heat flux over the shallow MLD region is a possible mechanism of maintaining the SST intraseasonal oscillation.