Principal Modes of Rainfall–SST Variability of the Asian Summer Monsoon: A Reassessment of the Monsoon–ENSO Relationship

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Abstract
Using global rainfall and sea surface temperature (SST) data for the past two decades (1979–98), the covariability of the Asian summer monsoon (ASM) and El Niño–Southern Oscillation (ENSO) was investigated. The findings suggest three recurring rainfall–SST coupled modes. Characterized by a pronounced biennial variability, the first mode is associated with generally depressed rainfall over the western Pacific and the “Maritime Continent,” stemming from the eastward shift of the Walker circulation during the growth phase of El Niño. The associated SST pattern consists of an east–west SST seesaw across the Pacific and another seesaw with opposite polarity over the Indian Ocean. The second mode is associated with a growing La Niña, comprising mixed, regional, and basin-scale rainfall and SST variability with abnormally warm water in the vicinity of the Maritime Continent and western Pacific. It possesses a pronounced low-level west Pacific anticyclone (WPA) near the Philippines and exhibits large sub... Abstract Using global rainfall and sea surface temperature (SST) data for the past two decades (1979–98), the covariability of the Asian summer monsoon (ASM) and El Niño–Southern Oscillation (ENSO) was investigated. The findings suggest three recurring rainfall–SST coupled modes. Characterized by a pronounced biennial variability, the first mode is associated with generally depressed rainfall over the western Pacific and the “Maritime Continent,” stemming from the eastward shift of the Walker circulation during the growth phase of El Niño. The associated SST pattern consists of an east–west SST seesaw across the Pacific and another seesaw with opposite polarity over the Indian Ocean. The second mode is associated with a growing La Niña, comprising mixed, regional, and basin-scale rainfall and SST variability with abnormally warm water in the vicinity of the Maritime Continent and western Pacific. It possesses a pronounced low-level west Pacific anticyclone (WPA) near the Philippines and exhibits large sub...