International Journal of Marine Science, 2024, Vol.14, No.3, 218-230 http://www.aquapublisher.com/index.php/ijms 222 2019). The Indian summer monsoon rainfall (ISMR) is also influenced by various modes of interannual climate variations, including ENSO, IOD, and ENSO Modoki, which have distinct teleconnections and impacts on monsoon variability (Behera, 2021). Additionally, the IPWP affects monsoon circulations, although its impact is less pronounced compared to its influence on the Hadley and Walker circulations (Kim et al., 2020). The regional coupled ocean-atmospheric feedback mechanisms in the Indo-northwest Pacific region further enhance the variance and persistence of atmospheric variability, influencing the Asian summer monsoon (Wang et al., 2020). 5 Ocean Circulation and Extreme Weather Events 5.1 Connection to tropical cyclones The variability in ocean circulation within the Indo-Pacific basin has a significant impact on the formation and intensity of tropical cyclones. The Madden-Julian Oscillation (MJO), a dominant mode of subseasonal variability, modulates tropical cyclones and monsoons, contributing to severe weather events across various regions including Asia, Australia, and the Americas (Roxy et al., 2019). The expansion of the Indo-Pacific warm pool has altered the MJO life cycle, which in turn affects the frequency and intensity of tropical cyclones (Roxy et al., 2019). Additionally, the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) are closely linked to changes in tropical cyclone activity, with positive IOD events and El Niño conditions generally leading to increased cyclone activity in the Indian Ocean (Abram et al., 2020; Kumar et al., 2021). 5.2 Influence on droughts and floods Ocean circulation patterns in the Indo-Pacific basin also play a crucial role in influencing droughts and floods. The IOD and ENSO are key drivers of these extreme weather events. For instance, the strong El Niño event in 2016 and the subsequent weak La Niña in 2017 significantly impacted sea surface temperatures (SST) in the tropical Indian Ocean, leading to extreme negative and weak positive IOD phases. These phases triggered floods in the Indian subcontinent and drought conditions in East Africa (Khan et al., 2021). The variability in the South China Sea monsoon trough, influenced by SST anomalies in the Indo-Pacific, also contributes to regional droughts and floods (Zhang et al., 2020b). The interaction between the Pacific and Indian Ocean waveguides, particularly through the Indonesian Throughflow (ITF), further modulates these extreme weather events by altering the distribution of warm and cold water masses (Feng et al., 2018). 5.3 Case studies of notable events Several notable events illustrate the impact of Indo-Pacific ocean circulation on extreme weather: (1) 1997 IOD Event: The most extreme positive IOD event on record occurred in 1997, which was associated with severe droughts in Indonesia and Australia, and flooding in East Africa. This event demonstrated the tight coupling between IOD and ENSO, and its significant impact on regional climate variability (Abram et al., 2020). (2) 2016-2017 ENSO and IOD Events: The strong El Niño in 2016 followed by a weak La Niña in 2017 led to extreme negative and weak positive IOD phases. These events caused significant flooding in the Indian subcontinent and drought conditions in East Africa, highlighting the complex interplay between ENSO and IOD in driving extreme weather (Khan et al., 2021) (Figure 2). (3) MJO and Rainfall Patterns: The rapid warming of the Indo-Pacific warm pool has altered the MJO life cycle, leading to increased rainfall over Southeast Asia, northern Australia, and the Amazon, while causing drying over the west coast of the United States and Ecuador. This shift in rainfall patterns underscores the broader impact of ocean circulation changes on global weather systems (Roxy et al., 2019). Khan et al. (2021) displays the yearly mean sea surface temperature (SST) anomalies in the Tropical Indian Ocean (TIO) for 2016 (a) and 2017 (b) relative to the 1981-2010 period. The black boxes represent the Western TIO (WTIO) and Eastern TIO (ETIO). Monthly SST anomaly trends are inset within the maps. In 2016, a strong Indian Ocean Dipole (IOD) event is observed, with cold anomalies in the WTIO and warm anomalies in the ETIO, peaking in September. This resulted in significant climate impacts due to suppressed atmospheric convection and enhanced surface energy flux. Conversely, 2017 experienced a weak positive IOD, with marginal SST anomalies.
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