Drivers and characteristics of the Indo-western Pacific Ocean capacitor

Abstract

Coherently coupled ocean-atmosphere variability of the tropical Indo-Pacific Oceans gives rise to the predictability of Asian summer climate. Recent advances in Indo-western Pacific Ocean capacitor (IPOC) theory and the relationship with El Niño-Southern Oscillation (ENSO) are reviewed. The IPOC features tropical Indian Ocean (TIO) warming and an anomalous anticyclonic circulation over the western North Pacific (WNPAAC), the latter driving water vapor transport to East Asia and causing extreme events, e.g., heavy rainfalls from central China to Japan during the boreal summer. IPOC events often occur in post-ENSO summers, but the significant TIO warming could sustain the WNPAAC without a strong El Niño, forced instead by a strong antecedent positive Indian Ocean Dipole (IOD). In latter cases, the Indian Ocean and WNP act as a self-sustaining system, independent of external forcings. El Niño or positive IOD induces the oceanic downwelling Rossby waves and thermocline warming in the southwest TIO, leading to SST warming and a “C-shaped” wind anomaly during winter and early spring. Furthermore, the southwest TIO downwelling Rossby waves reflect as oceanic Kelvin waves on the African coast. In the early summer, the resultant southeast TIO SST warming induces a second “C-shaped” wind anomaly. Both southwest and southeast TIO warming contribute to the WNPAAC. The WNPAAC modulates the water vapor pathways to East Asia in the late spring and summer, which mostly converge over the South China Sea and adjacent regions before flowing further to the north. More water vapor is transported from the western Pacific warm pool and less from the southern hemisphere and the Indian Ocean. The enhanced Asian Summer monsoon and moisture content lead to extreme rainfalls in central China and Japan during the boreal summer.

The Indian Ocean Dipole Modulates the Phytoplankton Size Structure in the Southern Tropical Indian Ocean

“…Both local wind forcing and oceanic Rossby waves exert substantial influence on the phytoplankton size structure in the central southern TIO from the development to the maturity of the IOD events. Previous studies found that downwelling oceanic Rossby waves associated with the anomalous anticyclonic wind stress curls in the southeast TIO deepen the thermocline and warm the subsurface in the southwestern TIO [35]. Our study also revealed that Rossby waves persisted in modulating the variations in phytoplankton size structure during IOD events.…”

“…Figure 5 presents longitude-tim sections of the CSD slope anomalies for the three strong positive and three strong nega tive IOD events. The IOD exhibits seasonal phase-locking characteristics, developin from late spring to early summer, strengthening in summer, peaking in autumn, an gradually diminishing in winter [35]. The variations in CSD slope anomalies in th southeastern TIO were generally consistent with the evolution process of the IOD (Fig ure 5).…”

“…This was primarily attributed to ocean-atmosphere interactions associated with the sustained warming in the southwestern TIO induced by Rossby waves during extreme positive IOD events in 2019 or the strong IOD event in 2015. Such SST warming triggered cross-equatorial "C-shaped" wind anomalies, leading to basin-wide warming via wind-evaporation-SST feedback [35,38]. Therefore, the sustained SST warming kept the upper ocean consistently lacking in nutrients.…”