Abstract
AbstractThis study identifies a new triggering mechanism of the Indian Ocean Dipole (IOD) from the Southern Hemisphere. This mechanism is independent from the El Niño‐Southern Oscillation (ENSO) and tends to induce the IOD before its canonical peak season. The joint effects of this mechanism and ENSO may explain different lifetimes and strengths of the IOD. During its positive phase, development of sea surface temperature cold anomalies commences in the southern Indian Ocean, accompanied by an anomalous subtropical high system and anomalous southeasterly winds. The eastward movement of these anomalies enhances the monsoon off Sumatra‐Java during May–August, leading to an early positive IOD onset. The pressure variability in the subtropical area is related with the Southern Annular Mode, suggesting a teleconnection between high‐latitude and midlatitude climate that can further affect the tropics. To include the subtropical signals may help model prediction of the IOD event.
Highlights
As a major intrinsic climate mode in the tropical Indian Ocean (IO), the Indian Ocean Dipole (IOD) has great impacts on the IO rim countries and over the globe (Cai, Cowan, & Raupach, 2009; Endo & Tozuka, 2015; Izumo et al, 2010; Qiu et al, 2014; Saji & Yamagata, 2003)
We suggest that if the subtropical high anomaly persists in the southern IO, the IOD could recur through the Southern Hemisphere Mechanism (SHM), for example, the 1976–1977 and 2006–2007 positive events
This study proposes a novel triggering mechanism of the IOD from the Southern Hemisphere (Figure 4)
Summary
As a major intrinsic climate mode in the tropical Indian Ocean (IO), the Indian Ocean Dipole (IOD) has great impacts on the IO rim countries and over the globe (Cai, Cowan, & Raupach, 2009; Endo & Tozuka, 2015; Izumo et al, 2010; Qiu et al, 2014; Saji & Yamagata, 2003). During a positive IOD event, sea surface temperature (SST) anomalously cools in the equatorial eastern IO while warms in the equatorial western IO; anomalous easterly wind prevails in the equatorial IO driven by the zonal pressure gradient, following the Bjerknes positive feedback (Bjerknes, 1969; Delman et al, 2016; Drbohlav et al, 2007; Saji et al, 1999; Webster et al, 1999; Yu et al, 2005). We show that subtropical high variability and high‐latitude activities in the Southern Hemisphere can induce an IOD event, which we refer to as the Southern Hemisphere Mechanism (SHM)
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