Relationship between SST anomalies and the intensity of intraseasonal variability

Abstract

Intraseasonal variability (ISV) is a primary source for the sub-seasonal prediction that affects the livelihood of billions of people. Interannual variation of ISV intensity is important for seasonal prediction of ISV impacts on severe weathers. Existing measures of overall tropical ISV intensity, however, do not show any significant simultaneous relationship with external sea surface temperature anomalies (SSTAs). In this study, it is proposed that the ISV intensity, represented by the seasonal standard deviation of the 30–90-day filtered outgoing longwave radiation (OLR), has a good relation with the external SSTAs. With this measure, two major components of the interannual variability of global ISV intensity are detected for both boreal summer and winter: EOF1 calls its variability over the central Pacific and EOF2 is associated with the variability over the Indo-Pacific Warm Pool region. More importantly, each of these two components is significantly related to SSTAs over a specific tropical region. The central Pacific ISV intensity is strong during central Pacific warming, while the ISV intensity is strong over the Indo-Pacific Warm Pool region during eastern Pacific cooling. The eastern and central Pacific warming has very different impacts on the ISV intensity: The eastern Pacific warming largely reduces the winter ISV intensity over the Indian Ocean, while the central Pacific warming only induces neutral winter ISV intensity anomalies over the Indian Ocean. In the summer, the ISV intensity variability is confined near the equator associated with the central Pacific warming; the eastern Pacific warming, however, induces large ISV intensity variability over the western North pacific because of strong northeastward propagation of the boreal summer ISV under the easterly vertical shear.