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The interactions between El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are known to have great implications for global climate variability and seasonal climate predictions. Observational analysis suggests that the ENSO–IOD inter‐basin connection is time‐varying and related to the Atlantic Multidecadal Oscillation (AMO) with weakened ENSO–IOD relationship corresponding to AMO warm phases. A suite of Atlantic pacemaker simulations successfully reproduces the decadal fluctuations in ENSO–IOD relationship and its link to the AMO. The warm sea surface temperature (SST) anomalies associated with the AMO drive a series of Indo‐Pacific mean climate changes through tropical‐wide teleconnections, including the La Niña‐like mean SST cooling over the central Pacific and the deepening of mean thermocline depth in the eastern Indian Ocean. By modulating ocean–atmosphere feedback strength, those mean state changes decrease both ENSO amplitude and the Indian Ocean sensitivity to ENSO forcing, therefore decoupling the IOD from ENSO. Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are two most important interannual climate signals exciting world‐wide climate and socioeconomic impacts. Their interactions are known to have great implications for global climate variability and seasonal climate predictions. However, the ENSO–IOD relationship is time‐varying and show prominent decadal fluctuations. Such changes in ENSO–IOD relationship are associated with the decadal variation in IOD teleconnections and predictability. The prediction skill of IOD is high when the ENSO–IOD relationship is strong, and vice versa. But it remains unknown what controls the decadal modulation of Indo‐Pacific inter‐basin connection. Our findings suggest that the Atlantic Multidecadal Oscillation (AMO) may modulate the ENSO–IOD inter‐basin connection. The AMO sea surface temperature anomalies drive a series of Indo‐Pacific mean climate changes through tropical‐wide teleconnections. Those mean state changes further influence both ENSO amplitude and the Indian Ocean sensitivity to ENSO forcing, thereby modulating the ENSO–IOD relationship. This study advances our understandings on inter‐basin and cross‐scale interactions in the climate system. Key Points: The inter‐basin connection between El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole is time‐varying and controlled by the remote Atlantic Multidecadal Oscillation (AMO)The AMO sea surface temperature anomalies drive a series of Indo‐Pacific mean climate changes through tropical‐wide teleconnectionsThe AMO induced mean state changes influence both ENSO amplitude and the Indian Ocean sensitivity to ENSO forcing [ABSTRACT FROM AUTHOR]

In June‐July 2020, the Middle and Lower Yangtze River Region (MLYR) encountered the most severe precipitation event over the past 60 years. The Indian Ocean Dipole (IOD) in the previous autumn of the unusual precipitation event was the main contributing factor. Nonetheless, not every strong IOD event could bring anomalously high precipitation in the MLYR. This study showed significantly enhanced influence of IOD on East Asia climate since 2000. The IOD's effect on MLYR summer precipitation has strengthened significantly with the correlation coefficient up to 0.55 during 2000–2020. The northward movement of East Asia–Pacific pattern associated with IOD since 2000 (as compared with before) was primarily responsible for the enhanced effect. Since 2000, the MLYR has been controlled by a deep baroclinic instability system with anomalous low pressure in the lower troposphere and anomalous high pressure (completely different from before). Furthermore, the western Pacific subtropical high shifted northward and westerly jets were significantly enhanced with eastward expansion. All of these patterns contributed to the water vapor convergence and precipitation generation in the MLYR, which was not the case in the past. The record‐breaking IOD in 2019 autumn and the enhanced IOD's climatic effect in 2000–2020 contribute to the extreme Meiyu in 2020 jointly. The significant change in the influence of IOD and the enhanced climate effect of IOD highlight exciting new avenues for improving climate predictions in the MLYR. Plain Language Summary: The excessive Meiyu rainfall over the Middle and Lower Yangtze River Region (MLYR) during summer 2020 was beyond expectations of meteorologists, because in the 2019/20 winter, the Niño3.4 index was marginal at only 0.5°C as compared to 2.4°C and 2.6°C in 1997/98 and 2015/16 winters, respectively. Researches pointed out that the severely positive Indian Ocean Dipole (IOD) in the previous season was the main contributing factor on 2020 extreme Meiyu event in the MLYR. Nonetheless, not every strong IOD event could bring anomalously high precipitation in the MLYR. Our study shows significantly enhanced influence of IOD on East Asia climate since 2000. The IOD's effect on MLYR summer precipitation has strengthened significantly with the correlation coefficient up to 0.55 during 2000–2020. The IOD‐induced circulation patterns, including East Asia–Pacific pattern, the western Pacific subtropical high, and westerly jets, shifted northward with stronger intensity since 2000 (as compared with before). These results help us to reconsider the influence of tropical Indian Ocean sea surface temperature when forecasting weather or the possible climate changes under global warming. Key Points: The impact of Indian Ocean Dipole (IOD) on the Yangtze precipitation has enhanced in recent decadesThe IOD‐induced East Asia–Pacific pattern moves northward since 2000The interdecadal change in IOD's climatic effect largely contributes to the extreme Meiyu in 2020 [ABSTRACT FROM AUTHOR]

Indian Ocean Dipole (IOD) prediction is a challenging problem, largely relying on the relationship between IOD and El Niño‐Southern Oscillation (ENSO). This study demonstrates that heat content internal to the Indian Ocean can be an effective predictor providing extra IOD predictability, through constructing statistical prediction models with and without heat content as a predictor. Two recently proposed heat content predictors, equatorial heat content (EQHC) and heat content in the eastern pole of the Dipole (SEHC) are compared in this study. Results show that EQHC is more effective partly because it is relatively independent of ENSO and partly because it does not rely on IOD persistence, as does SEHC. The efficacy of EQHC as an IOD predictor is seasonally dependent, being most effective at 5–8‐month lead times beginning in the preceding late boreal winter and spring. Plain Language Summary: The Indian Ocean Dipole (IOD), a major climate mode in the tropical Indian Ocean, can lead to severe floods and droughts over surrounding continental areas. Prediction of the IOD is very challenging due to the apparent lack of effective predictors besides the El Niño‐Southern Oscillation. This study compares two recently proposed predictors for the IOD based on upper ocean heat content, one along the equator and one in the southeastern tropical Indian Ocean. Equatorial heat content proves to be more effective, especially for predictions starting in the late boreal winter and spring. This study helps to improve our understanding of IOD dynamics and its predictability. Key Points: Heat content internal to the Indian Ocean provides IOD predictability in addition to El Niño‐Southern Oscillation, especially at 5–8‐month lead timesHeat content as a predictor is seasonally dependent, being most effective as an initial condition in the boreal winter and springEquatorial heat content is more useful than heat content in the eastern pole of the Dipole as a predictor when accounting for persistence [ABSTRACT FROM AUTHOR]

Key points 1. Correlation map analysis between ENSO and IOD’s sea surface temperature with burned area. 2. Behaviour analysis of burned area in Indonesia in response to ENSO and IOD. 3. Identify and quantify the impact of ENSO-IOD’s teleconnection in Indonesia.

• Internal waves are regularly observed at a shallow tropical seamount ecosystem. • The internal wave regime is controlled by background stratification and forcing. • Thermocline depth relative to summit depth modulates the internal wave regime. • Basin scale processes drive stratification variation over interannual timescales. Shallow seamounts are becoming increasingly recognised as key habitats for conservation due to their role as biological refuges, particularly throughout oligotrophic oceans. Traditionally, Taylor caps have been invoked as the mechanism driving biomass aggregation over seamounts but emerging evidence based on higher resolution measurements highlights the importance of internal waves (IW) to the local ecosystem. These waves can flush the benthic habitat with cool water from depth and impact on nutrient supply over short time scales through turbulent mixing that may also influence fish behaviour. They are dependent on the regional stratification, however, and thus influenced by planetary-scale variability in oceanographic conditions. We present here detailed observations of the internal wave regime over a shallow seamount, called Sandes, in the central Indian Ocean throughout different phases of the Indian Ocean Dipole (IOD) that modulated the regional stratification. A deep thermocline, caused by the 2019 IOD event precluded internal wave activity over the summit, whereas a thermocline collocated with the summit during 2020 when the IOD reversed polarity resulted in a 30 m amplitude internal tide signal (t ∼ 12.5 h). A shallow thermocline, observed during 2022, resulted in propagation of IWs over the summit with less visible internal tide. Harmonic analysis shows the presence of high frequency waves (t ∼ 15 min) on both flanks of the seamount during 2020 & 2022, which are likely a result of local shear instability, whereas 2019 shows an asymmetric response, potentially due to the strong background current and suppression of the thermocline beneath the depth of the summit. The potential importance of the waves over the summit to the local ecosystem may be attributed to the elevated turbulence measured at the thermocline during internal wave propagation, with ε > 10-5 W kg-1 routinely observed. Our results highlight the ability of thermocline depth to act as a gating condition for internal wave evolution over the summit. These results show that, whilst the water column exhibits variability at short spatiotemporal scales compared to the frequently cited Taylor cap dynamics, it is also regulated by the wider basin scale processes. Thus, a more integrated approach is needed when assessing these dynamic and environmentally critical habitats to include the effects of physical oceanographic controls across multiple spatiotemporal scales. [ABSTRACT FROM AUTHOR]

Indian Ocean (IO) warming, the frequency of extreme positive Indian Ocean Dipole (EPIOD) events, and its impact on Indian monsoon rainfall (IMR) are more prominent in the recent era. A proper understanding of the relationship between the EPIOD and IMR is very important because two thirds of the people in India are dependent on agriculture and related economy. The primary focus of this study is on three main aspects: (i) analysing the monthly trend of sea surface temperature (SST) in the IO; (ii) the spatial variability of SST anomalies (SSTA) linked to the EPIOD and its impact on the IMR; and (iii) the factor responsible for the intensification of the EPIOD. These aspects are thoroughly assessed using 12 NMME models, comparing them with observations and reanalysis datasets from 1990 to 2020. The analysis reveals a warming trend in the central IO during June and July, with significant increases observed from August to November. Over the past 31 years, the central IO has experienced an approximate rise of 0.9 to 1 °C from June to November. Among the 12 models scrutinised, GFDL_FLOR_A, FLOR_B, and RSMAS_CCSM4 closely align with observed spatial trends. In contrast, models such as GFDL_SPEAR and NASA_GEOSS tend to overestimate these spatial trends. An increase in easterlies over the equatorial eastern IO was identified as a possible driver for the rising SST in the central IO during October and November. In response to EPIOD on the monthly spatial rainfall distribution over India, all NMME models often underestimate rainfall over the west coast and exhibit wet biases over the leeward side of the Western Ghats. Grid-wise skill scores for accumulated monthly rainfall demonstrated variations among NMME models, with GFDL_SPEAR, RSMAS_CCSM4, and other IC3 models showing higher skill. The interhemispheric pressure gradient (IHPG) has been identified as a precursor to EPIOD events. A positive IHPG from March to June is correlated with EPIOD occurrences from October to December. It is observed that half of the NMME models are capable of simulating a positive relationship between IOD and IHPG, consistent with the observed data. • The study highlights IO warming mechanism, EPIODE formation, and their relation to the IMR in observations and NMME models. • The cause of IO warming is attributed to an increase in low-level Easterlies wind strength over the central equatorial IO. • EPIODE formation, driven by interhemispheric pressure gradient, serves as a precursor. • The GFDL_SPEAR and RSMAS_CCSM4 models effectively capture monthly rainfall during EPIODE. [ABSTRACT FROM AUTHOR]

The interannual rainfall variability over the southeast Australian state of Victoria is known to be influenced by a number of large scale and regional phenomena, including the Indian Ocean Dipole (IOD), Southern Oscillation Index (SOI), and Southern Annular Mode (SAM). However, the role of 'upstream' regional circulation or pressure anomalies has received only modest attention. The amount of winter (May-August) rainfall over the state has declined over the past few decades, especially from 1960 to 2017. Using the Center of Action (COA) technique this study examines the relationship between winter precipitation over Victoria and the characteristics of the Indian Ocean High (IOH) over the period 1951–2021. We show that variations of the IOH are strongly linked with those of precipitation over Victoria. The strongest link is with the Indian Ocean High pressure (IOH_P) and its longitudinal position (IOH_LN), whereas the Indian Ocean High latitude (IOH_LT) has little impact. Less precipitation is observed across the state when IOH_P anomalies are positive, whereas the eastward shift of the IOH_LN is a major factor in the reduction of precipitation. Using correlation and multiple regression analyses, we find that the IOH indices explain 54 % of the winter precipitation variation. The strength of this relationship is somewhat weaker in the northern part of the state, partly because of the additional influence of 'north-west cloud bands' north of the Great Diving Range. Finally, we perform composite analyses of anomalous high (low) years of IOH to establish evidence of IOH influencing Victorian rainfall. This allows us to reveal the dynamical mechanisms behind the revealed associations. • The Center of Action approach is used to determine the relationship between sea level pressure fields and winter precipitation over Victoria. • The Indian Ocean High has a significant impact on the variation in Victoria's winter rainfall. • Droughts in Victoria are associated with high positive extreme values in Indian Ocean. [ABSTRACT FROM AUTHOR]

Global climatic circulation indices play a major role in determining regional and global climate conditions. These atmospheric circulation patterns exhibit substantial variability, covering a wide geographical area and affecting weather-related events. The primary goal of this study was to examine and characterize various global climatic variability indices during the 1950 to 2020 period (El Niño Southern Oscillation, ENSO; Southern Oscillation Index, SOI; North Atlantic Oscillation, NAO; Atlantic Meridional Mode, AMM; and Indian Ocean Dipole, IOD). Also, this article try to investigating the link between these global climatic indices. Trend analysis showed that the ENSO index exhibits the highest recurrence frequency of correlation relationships with the other yearly global indices with significance at the 95% and 99% levels, while the NAO index exhibits the lowest recurrence frequency. On a seasonal basis, most indices demonstrate more abrupt changes during the winter season than during the summer. An increase occurred in events of abrupt changes in these indices over the last two decades (2000 to 2020), especially annually and in summer. The SOI exhibits the largest number of abrupt changes throughout the entire study period, spanning from positive to negative significant trends, whereas the IOD did not exhibit abrupt changes annually. Increasing and decreasing trends in the global climatic circulation indices may be related to natural and anthropogenic causes of climate change. Regarding both the correlation coefficient (CC) and partial correlation results, there existed a highly negative association between the ENSO and SOI in the annual, winter and summer time series. On the other hand, there is no relationship between ENSO and NAO. Furthermore, on an annual basis, there existed a highly negative association between the NAO and AMM and a less negative but still statistically significant association between these indices during the winter and summer seasons, respectively. Therefore, through the Azore high, the NAO could promote AMM. Moreover, when the NAO, AMM, and SOI are held constant, a positive and robust correlation is reached between the ENSO and IOD in winter season. Therefore, a developing IOD is intensified and sustained during the onset of an El Niño event in winter season.

This study focuses on the regional wind variability that controls the intensity of cold-water upwelling off Sumatra – a key feature of the Indian Ocean Dipole (IOD). Our analysis of daily atmospheric data reveals the existence of convectively triggered synoptic-scale atmospheric cyclones in the South-East Tropical Indian Ocean (SETIO). The northern branch of the cyclones corresponds to westerly equatorial wind events, whereas the eastern branch involves north-westerly winds that operate to suppress cold-water upwelling off Sumatra’s west coast. Data for the period 1988–2022 show that 5–9 SETIO cyclones normally form each year during the boreal summer–autumn season, effectively suppressing upwelling in the region. In contrast, there are only few (1–2) cyclone events in years identified as positive phases of the IOD, when the absence of cyclones concurs with the development of strong coastal upwelling off Sumatra. Our findings suggest that the absence or presence of SETIO cyclones contributes to IOD variability.

Abstract The tropical Indian Ocean (TIO) basin-wide warming occurred in 2020, following an extreme positive Indian Ocean Dipole (IOD) event instead of an El Niño event, which is the first record since the 1960s. The extreme 2019 IOD induced the oceanic downwelling Rossby waves and thermocline warming in the southwest TIO, leading to sea surface warming via thermocline-SST feedback during late 2019 to early 2020. The southwest TIO warming triggered equatorially antisymmetric SST, precipitation, and surface wind patterns from spring to early summer. Subsequently, the cross-equatorial “C-shaped” wind anomaly, with northeasterly–northwesterly wind anomaly north–south of the equator, led to basin-wide warming through wind-evaporation-SST feedback in summer. This study reveals the important role of air–sea coupling processes associated with the independent and extreme IOD in the TIO basin-warming mode, which allows us to rethink the dynamic connections between the Indo-Pacific climate modes.

Many parts of East Africa experienced extremely dry conditions during the short rains season of October–December 2021. It was predicted a few months before by the ensemble seasonal prediction system based on the SINTEX‐F climate model. The analysis of co‐variability of inter‐member anomalies has revealed that the 2021 negative Indian Ocean Dipole was responsible for these unusually dry conditions over East Africa. We also show that a hybrid statistical‐dynamical framework is more skillful than the SINTEX‐F model at predicting drought in East Africa on longer lead time, which may help people to take necessary mitigation measures to reduce the devastating impact of the drought. Plain Language Summary: Many parts of East Africa experienced extremely dry conditions during the short rains season (October–December) of 2021. Such a devastating drought in East Africa leads to unsafe drinking water, food insecurity, and other socio‐economic issues. We found the 2021 negative Indian Ocean Dipole (IOD) was responsible for these unusually dry conditions over East Africa. The IOD is an intrinsic ocean–atmosphere coupled climate phenomenon in the tropical Indian Ocean with cold (warm) sea surface temperature anomalies and reduced (enhanced) rainfall in the western (eastern) tropical Indian Ocean during its negative phase. Some of the devastating droughts (severe floods) in East Africa are observed during negative (positive) IOD years, respectively. Improved predictions of the IOD and its impacts may help us develop necessary mitigation measures to reduce the devastating impacts. Key Points: East Africa suffered from an extreme drought during the short rains season of October–December 2021The 2021 negative Indian Ocean Dipole was responsible for the devastating drought and played a key role in its seasonal predictabilityA hybrid statistical‐dynamical prediction of drought in East Africa on longer lead time may help people to take mitigation measures [ABSTRACT FROM AUTHOR]

The 2019 extreme positive Indian Ocean dipole drove climate extremes over Indian Ocean rim countries with unclear carbon‐cycle responses. We investigated its impact on net biome productivity (NBP) and its constituent fluxes, using the Global Carbon Assimilation System (GCASv2) product, process‐based model simulations from TRENDYv9, and satellite‐based gross primary productivity (GPP). By distinguishing two separate regions, the India‐Africa and Asia‐Pacific, GCASv2 indicated enhanced terrestrial carbon uptake of 0.23 ± 0.20 PgC and release of 0.38 ± 0.15 PgC, respectively, during September–December (SOND) 2019. These NBP anomalies had comparable magnitudes to those following the 2015 extreme El Niño which, however, caused the consistent carbon release in both regions. The TRENDYv9 model ensemble confirmed these NBP responses, albeit with smaller magnitudes. These regional NBP anomalies were related to soil moisture variations with a dominant role of GPP. Understanding the impact of IOD provides new insights into mechanisms driving interannual variations in regional carbon cycling. Plain Language Summary: The extreme Indian Ocean Dipole (IOD) can drive climate extremes, such as floods, heatwaves, droughts, and wildfires, over the Indian Ocean rim countries. However, responses of regional terrestrial carbon cycling to IOD remained unclear. We used the net biome productivity (NBP) from an atmospheric inversion and multiple terrestrial biosphere models to demonstrate an enhanced terrestrial carbon uptake and release over the India‐Africa and Asia‐Pacific regions, respectively, during the extreme positive IOD (September–December) in 2019. These IOD‐induced regional NBP anomalies showed comparable magnitudes but different patterns to those following the 2015 extreme El Niño. Along with the more frequent extreme IOD under future greenhouse warming, IOD will be an important mechanism driving interannual variations in regional carbon cycling. Key Points: The 2019 extreme positive Indian Ocean Dipole caused the enhanced land carbon uptake over India‐Africa and release over Asia‐Pacific during September–DecemberThese regional net biome productivity (NBP) anomalies were closely related to soil moisture variations with a dominant role of gross primary productivityThese Indian Ocean Dipole‐induced regional NBP anomalies showed comparable magnitudes but different patterns to those following the 2015 extreme El Niño [ABSTRACT FROM AUTHOR]

The evolution of an extreme positive Indian Ocean Dipole (pIOD) that took place in the tropical Indian Ocean during the late boreal summer to early winter of 2019 is examined in terms of coupled ocean–atmosphere dynamics. The patterns of anomalous sea-surface temperature (SST) revealed a typical pIOD characteristic: cooling (warming) in the southeastern (western) tropical Indian Ocean. Based on the Dipole Mode Index (DMI), the evolution of the event started in mid-July and gradually strengthened with an abrupt weakening in early September before coming to its peak in late October/early November. It quickly weakened in November, and then it terminated in mid-December. During the peak phase of the event, the SST anomaly in the southeastern (western) tropical Indian Ocean reached about −2 °C (+1 °C). The pattern of anomalous SST was followed by an anomalous pattern in precipitation, in which deficit precipitation was observed over the eastern Indian Ocean, particularly over the Indonesia region. Earlier study has shown that dry conditions associated with the pIOD event created a favorable condition for a forest-peat fire in southern Sumatra. The number of fire hotspots has increased significantly during the peak phase of the 2019 pIOD event. In addition, anomalously strong upwelling forced by strong southeasterly wind anomalies along the southern coast of Java and Sumatra had induced a surface chlorophyll-a (Chl-a) bloom in this region. High surface Chl-a concentration was collocated with the negative SST anomalies observed off the southwest Sumatra coast and south Java. [ABSTRACT FROM AUTHOR]

Interannual variability of the Indian Summer Monsoon Rainfall (ISMR) is modulated by Sea Surface Temperature (SST) anomalies over Indo-Pacific Oceans, especially by the El Niño Southern Oscillation (ENSO). In general, coupled models used for seasonal prediction overestimate the correlation between ENSO and ISMR compared to observations. By analysing the observational data from 1982 to 2017, this study shows that the relationship between ENSO and ISMR is weak during August compared to the other months of the summer monsoon season (June, July, and September). This weak association between ENSO and ISMR during August is due to an increase in the synoptic variability. Thus, the effect of large-scale flow dominated by ENSO is suppressed by the formation of a synoptic system in the Bay of Bengal (BoB), making ENSO-ISMR relation feeble in August. The data analysis of various coupled models shows that all models underestimate synoptic variability, due to which simulated ENSO-ISMR relation is overestimated during August. Coupled model exhibit strong biases in relative humidity and cyclonic circulation over the northern BoB hence underestimating the synoptic variability. [ABSTRACT FROM AUTHOR]

Based on the Argo and multi‐satellite observations, this study investigates the asymmetric response of sea surface salinity (SSS) to two extreme positive and negative Indian Ocean Dipole (IOD) events in the southern tropical Indian Ocean (TIO). During positive IOD events, the easterly wind anomalies trigger zonal freshwater advection along the equator, decreasing SSS, while cold sea surface temperature (SST) depress the convective precipitation in the southeastern TIO (SETIO), increasing the SSS. Contrast SSS anomalies along the equator and in the SETIO show opposite phases during positive and negative IOD events. These SSS anomalies have enhanced in recent years, reaching the strongest in the extreme negative IOD in 2016 and positive IOD in 2019. The case study shows that positive SSS anomalies occurred in the southern TIO during both positive and negative IOD events in 2016 and 2019, suggesting significant asymmetry in SSS. Analysis of the mixed layer salinity budget shows that the local precipitation and the entrainment associated with the upwelling Rossby waves played an essential role in the SSS increase in 2016, while the decreased precipitation and horizontal advection caused by the westward South Equatorial Current contributed to the SSS increase in 2019. Further analyses suggest that SSS response is more sensitive to thermocline shoaling than deepening, and SSS response to precipitation is greater at shallower mixed layer than at deeper ones, which is the main reason for the asymmetric response of the SSS to negative and positive IOD events. Plain Language Summary: Indian Ocean Dipole (IOD) is one of the leading climate modes in the Indian Ocean, which impacts changes in temperature, precipitation, and salinity. This study reveals significant asymmetric responses in SSS during the decay phase of positive and negative IOD events. During the mature phase of positive and negative IOD events, there are opposite changes in sea surface temperature, atmospheric circulation, rainfall, and SSS in the equatorial and southeastern tropical Indian Ocean (SETIO). However, SSS increases in the SETIO during the decay phase of both positive and negative IOD events, revealing an asymmetric feature. This asymmetric structure of SSS anomalies has strengthened recently and reached extremes in the 2016 negative IOD event and the 2019 positive IOD event. The upwelling (downwelling) Rossby waves play an important role in the asymmetric response of SSS anomalies in the southern TIO since the SSS response is more sensitive to thermocline shoaling than deepening, and the shallower mixed layer may imply the SSS response to precipitation anomaly. Key Points: Contrast sea surface salinity (SSS) anomalies occur in the equatorial and southeastern tropical Indian Ocean (TIO) during the mature phases of Indian Ocean Dipole (IOD)SSS anomalies are out of phase during positive and negative IOD events but show an asymmetric change in the southern TIOThe asymmetry is due to different SSS responses to precipitation and thermocline changes associated with the ocean Rossby waves [ABSTRACT FROM AUTHOR]

In 2018-2021, several natural phenomena occurred that caused climate change in Indonesia. This climate change is estimated to have affected the dynamics of rainfall and temperature in Indonesia. This study aims to analyze the incidence of climate change, rainfall dynamics, and temperature dynamics, and find the correlation between rainfall versus temperature during the 2018-2021 dry season. The location of this research is on peatlands in Central Kalimantan and West Kalimantan where both locations have installed automatic measurement stations for rainfall and temperature. Peatlands were chosen because the dynamics of rainfall and temperature greatly affect the condition of peatlands that are prone to fires and floods. The results of this study indicate that very minimal rainfall occurs in the dry season in 2019, especially from July to September 2019. Rainfall in the 2019 dry season is much lower when compared to the dry season in 2018, 2020, and 2021. This happens because in 2019 two natural phenomena occurred simultaneously, namely: moderate IOD+ and weak El Niño. These two phenomena reinforce each other in reducing rainfall in Indonesia. The temperature during the dry season for 4 years did not show a significant difference, but in general, the temperature in Central Kalimantan was lower than the temperature in West Kalimantan. It was also found that there was a trend in the relationship between rainfall and temperature where the higher the rainfall, the lower the temperature. Based on the results of the statistical method of linear regression and t-test, it has been found that the correlation between rainfall and temperature is significant. [ABSTRACT FROM AUTHOR]

Using mooring observations and reanalysis, we show that anomalously strong westward Equatorial Undercurrent (wEUC) developed in June–July in 2016 and 1998 in the Indian Ocean, which coincided with extreme Indian Ocean Dipole (IOD) and El Niño events. Simulations show that equatorial Kelvin and Rossby waves were excited by winds associated with El Niño and positive IOD events during 2015 and 1997, and their negative phases during 2016 and 1998. The constructive relationship between the delayed‐time contributions of eastern‐boundary‐reflected‐waves that excited by the easterlies in 2015 and 1997 and the direct contributions of wind‐forced‐waves that excited by the westerlies in 2016 and 1998 resulted in the intensified wEUC. Slow intermediate‐order baroclinic‐modes, rather than fast low‐order baroclinic‐modes, dominated the strong wEUC. The eastern‐boundary‐reflected‐waves dominated in 1997–1998 and directly wind‐forced‐waves dominated in 2015–2016. Our results emphasize the importance of constructive interactions of the directly‐wind‐forced and boundary‐reflected waves in driving the interannual variability of Indian Ocean wEUC. Plain Language Summary: This study investigated the unique westward Equatorial Undercurrent (wEUC) and its associated dynamics in the Indian Ocean. Mooring observations at (80°E, 2.5°N) reveal the occurrence of an anomalously strong wEUC between 100 and 200 m depth in June‐July (JJ) 2016. Simulations show that the constructive relationship between the directly forced and boundary‐reflected waves resulted in the unprecedentedly strong wEUC in JJ 2016. Equatorial Kelvin and Rossby waves were excited by winds associated with El Niño and a positive Indian Ocean Dipole (IOD) during 2015, and their negative phases during 2016. Waves excited in 2015 hit the meridional boundary, and boundary‐generated waves propagated into the interior Indian Ocean in 2016, which were superposed onto the directly forced waves. A similar wave‐induced enhanced wEUC also occurred during the 1997–1998 strong El Niño and IOD events but with the dominant contribution coming from the eastern‐boundary‐reflected waves. Key Points: An anomalously strong westward Equatorial Undercurrent (wEUC) was observed in June–July (JJ) 1998 and 2016The intensified wEUC in JJ 1998 and 2016 was driven by the co‐occurrence of strong IOD and ENSO events during 1997–1998 and 2015–2016The dynamics are related to both directly wind‐driven and eastern‐boundary‐reflected intermediate‐order baroclinic waves [ABSTRACT FROM AUTHOR]

In this paper, we report on the frequency of false onsets of wet season rainfall in the case of the Northern Australian wet season and investigate the role of large‐scale tropical climate processes such as the El Niño–Southern Oscillation, Indian Ocean Dipole (IOD) and Madden–Julian Oscillation. A false onset occurs when a wet season rainfall onset criterion is met, but follow‐up rainfall is not received for weeks or months later. Our analysis of wet season rainfall data from 1950 through 2020 shows a false onset occurs, on average, between 20 and 30% of wet seasons across all of northern Australia. This increases at a regional and local level such as at Darwin, the Northern Territory (NT), and parts of Queensland's north coast to over 50%. Seasonal climate influences, such as a La Niña pattern and a negative IOD that typically expedite the wet season rainfall onset, also increase the likelihood of a false onset over northern Australia. Our analysis also finds that periods of false onsets can sometimes, but not always, coincide with periods of rapid soil moisture depletion. The false rainfall onsets that develop into flash drought can be potentially disruptive and costly and are of potential significance for agriculture and fire management in northern Australia, and in other monsoonal climates that also typically experience a slow build‐up to the seasonal monsoon. In conclusion, effective rainfall indicates that many seasons experience 'false onsets' with dry conditions after early rainfall. We propose that false onsets are a physical characteristic of the climate of northern Australia which occurs with relatively high frequency. In addition, these false onsets may sometimes co‐occur with a flash drought. [ABSTRACT FROM AUTHOR]

Although climate models are important for making projections of future climate, little attention has been devoted to model simulation of the complex climate of Central Africa (CA). This study investigates rainfall biases through processes in three versions of the Met Office Unified Model over CA with both coupled and atmosphere‐only formulations for each version. The study shows that the models depict a wet (dry) bias over the eastern (coastal western) CA in the September–November season with the wet (dry) bias stronger in coupled (atmosphere‐only) models. Here, we explore potential regional to large‐scale causes of these biases. Results reveal that the overestimation of the simulated sinking branch of the Atlantic‐Congo zonal overturning cell is associated with a strong near‐surface temperature and pressure gradient between CA and the eastern Atlantic Ocean. This leads to strong low‐level westerlies (LLWs) which dry the coastal western CA and strengthen the intensity of the Congo basin cell. Over eastern CA, the wet bias is partially due to the misrepresentation in the strength of both African easterly jet components that shift the mid‐tropospheric moisture flux convergence southward favouring more convection south of the equator. Furthermore, the overestimation in the simulated width and intensity of the Congo basin cell is associated with a strong low‐level moisture convergence over eastern CA which contributes to more precipitation. Remote contributions to the wet bias come from both the Atlantic and the Indian Oceans. The simulated Atlantic‐Congo zonal overturning circulation dries the coast through its overestimated lower branch (LLWs) which moves further into the continent and advects more moisture to the eastern CA. In the meantime, during positive Indian Ocean Dipole years, the advected moisture from the Indian Ocean to the CA region is overestimated in models, much more in coupled models and contributes to the eastern CA wet bias. [ABSTRACT FROM AUTHOR]

The three strongest positive Indian Ocean dipole (pIOD) events over the past four decades occurred in 1994, 1997, and 2019 and caused severe social-economic impacts in the Indian Ocean (IO) rim countries. These three strongest positive pIOD events exhibited similar oceanic and atmospheric anomaly patterns during their mature phase, though with different physical origins. The extreme amplitudes of these pIOD events were closely related to concurrent El Niño or Madden–Julian oscillation (MJO) activity. For the 1997 extreme pIOD case, the concurrent extreme El Niño in the Pacific triggered strong easterly wind anomalies over the equatorial IO and therefore favored the rapid growth of the pIOD via intense upwelling along the Sumatra-Java coast. In contrast, the long stalled MJO convective anomalies over the western IO exerted an important role in the 2019 extreme pIOD event especially during September–October by causing easterly anomalies over the equatorial IO. During that year, the Pacific moderate warming had likely a small impact since no strong associated convection was present over the western and central equatorial Pacific due to the small amplitude of the Pacific sea surface temperature anomalies. Different from the 1997 and 2019 cases, both El Niño conditions in the Pacific as well as MJO activity over the western IO contributed to the 1994 extreme pIOD event. Our results emphasize that MJO activity should be considered as one physical drivers for the extreme pIOD event in addition to the traditional El Niño-associated forcing. [ABSTRACT FROM AUTHOR]

The open ocean region of southern Bay of Bengal (BoB) (~ 5° N–10° N; 87° E–97° E) is characterized as the region of low chlorophyll-a concentration (< 0.1 mg m−3) during winter (December-February). However, the analysis of satellite ocean colour data between 2003 and 2020 shows anomalous high surface chlorophyll concentration (~ 0.35–0.5 mg m−3) in the southern BoB during the winters, followed by the extreme positive Indian Ocean Dipole (pIOD) events in 2006 (W06-2007) and 2019 (W19–2020). It is found that anomalous upwelling Rossby wave generated remotely through the anomalous easterly wind in the equatorial Indian Ocean (EIO) during October–November leads to a thin barrier layer (BL), shallow thermocline and nutricline in the southern BoB during W06–2007 and W19–2020. Thin BL, and shallow nutricline, provide a conducive environment for surface chlorophyll enhancement through much easier vertical transport of nutrient-rich water to the near-surface layer by local near-climatological wind-induced vertical mixing during W06–2007 and W19–2020. It is also found that surface chlorophyll bloom was absent in the southern BoB during the winters, followed by the weak pIOD event in 2012, 2015, and 2018. During the winters followed by the weak pIOD events, the westward propagating downwelling Rossby wave generated through the westerly wind, similar to the climatological state, in the EIO during October–November leads to a thick BL, deeper thermocline and nutricline in the southern BoB. Thick BL, and deeper nutricline, provide an unfavourable environment for the vertical transport of nutrient-rich water to the near-surface layers to generate surface chlorophyll bloom during the winters followed by the weak pIOD event. [ABSTRACT FROM AUTHOR]

Abstract The termination of Indian Ocean Dipole (IOD) events is examined in terms of equatorial wave dynamics. In situ and satellite observations combined with an output from a linear wave model are used in this study. Our emphasis is on the 1997 IOD event but our results apply to other positive IOD events as well. We find that the termination of anomalously cold sea surface temperature (SST) in the eastern pole of the dipole is associated with a warming tendency caused by the net surface heat fluxes. However, net surface heat fluxes alone cannot explain the total change in the SST. We show that during the peak phase of an IOD event, the weakening of zonal heat advection caused by eastern boundary-generated Rossby waves combined with the reduction of vertical entrainment and diffusion creates favorable conditions for surface heat fluxes to warm the SST in the eastern basin.

The lag correlations between the observed sea surface temperature anomalies (SSTA) in the southeastern tropical Indian Ocean in fall and those in the Pacific cold tongue at the one-year time lag are calculated in running windows of 7–11 years and are shown to have decadal variability. Similar decadal variability has also been identified in the historical simulations of the Community Climate System Model version 4 (CCSM4) that participates in the Coupled Model Intercomparison Project phase-5 (CMIP5). During the positive phases of the decadal variability, the significant lag correlations are diagnosed to be dominated by the oceanic channel dynamics, i.e., upwelling Kelvin waves associated with the Indian Ocean Dipole (IOD) force enhanced Indonesian Throughflow transport anomalies and western Pacific thermocline anomalies to propagate eastward, resulting in SSTA in the central-eastern equatorial Pacific Ocean. During the negative phases of the decadal variability, the subsurface lag correlations suggest that the western Pacific Ocean are still dominated by the oceanic channel dynamics, but do not correlate well with the SSTA in the cold tongue due to a deeper thermocline in the eastern equatorial Pacific. The IOD-ENSO teleconnection is not affected significantly by the anthropogenic forcing during either the positive or the negative decadal phases. The CCSM4 model is found to underestimate Indonesian Throughflow transport variability but overestimate the westerly wind anomalies in the western-central equatorial Pacific, which forces unrealistic anomalies in the equatorial Pacific Ocean associated with the IOD.

Coastal upwelling along the southern coast of Java brings cold and nutrient‐rich subsurface water to the surface. We explored whether the upwelling could trigger the onset of the Indian Ocean Dipole (IOD) by supplying cold water to the southeastern tropical Indian Ocean. We used satellite‐based daily chlorophyll‐a concentration (Chl‐a) data during 2003–2020 as a proxy of the coastal upwelling. We focused on first Chl‐a bloom that occurred in April‐June, the onset phase of the positive IOD (pIOD). We found that the timing and strength of the upwelling signals were significantly correlated with the subsequent IOD peaks. We diagnosed processes associated with the upwelling affecting sea surface temperature (SST) in the southeastern Indian Ocean. Results indicate that after the cold‐water upwelling south of Java, westward surface temperature advection plays a role in anomalously cooling the SST in the southeastern Indian Ocean and setting a favorable condition for the subsequent pIOD development. Plain Language Summary: Along the southwestern coastal waters of Java islands in Indonesia, coastal upwelling brings up cold water from below and can cool the ocean surface temperatures. Past studies reported that strong upwelling signals were observed together with the positive Indian Ocean Dipole (IOD) phenomenon. However, it was unclear if and how the coastal cold water spreads over large area of the Indian Ocean and affect the occurrence of IOD. We used sea surface chlorophyll‐a (Chl‐a) data estimated from satellite observations as an indicator of coastal upwelling. We focused on the date when the first Chl‐a bloom occurred south of Java in each year. On average, Chl‐a bloom occurs around June, but in years when it occurred earlier (around April‐May), Chl‐a bloom was followed by a positive IOD event in August‐October. We further investigated how the cold water in the coastal area spreads widely over the eastern Indian Ocean. It was found that stronger westward ocean currents expanded the cold water to a wider area of the eastern Indian Ocean and can set a favorable condition for the development of the positive IOD. Thus, accurate observation and understanding of the coastal upwelling may improve the predictability of the Indian Ocean climate. Key Points: Satellite‐based surface chlorophyll‐a (Chl‐a) can be a proxy of intraseasonal‐scale coastal upwelling along the southern coast of JavaThe timing and strength of the upwelling signals were significantly correlated with the subsequent peak of the Indian Ocean Dipole (IOD)The coastal upwelling may contribute to the onset and development of positive IOD through the process of anomalous cold‐water advection [ABSTRACT FROM AUTHOR]

The respective influences of the Indian Ocean dipole (IOD) and El Niño‐Southern Oscillation (ENSO) on the thermocline depth (represented by the 20°C isotherm depth, D20) variability in the south‐central Indian Ocean (SCIO) are investigated for the period of 1960–2020. The results show that pronounced interannual variations in D20 mainly occur in the SCIO and display a close relationship with the two tropical climate modes, with positive (negative) phase being associated with SCIO D20 deepening (shoaling). The D20 anomalies (D20A) induced by IOD and ENSO events have the same intensities but present different spatial–temporal features, as demonstrated by partial regression analysis. The IOD‐related D20A occurs during the mature phase of the event and behaves as a local response to anomalous wind stress curl induced by IOD, while the ENSO signature, dominated by the westward‐propagating oceanic Rossby waves, lasts much longer and extends further west. [ABSTRACT FROM AUTHOR]

The East African 'short rains' in October–December (OND) exhibit large interannual variability. Drought and flooding are not unusual, and long-range rainfall forecasts can guide planning and preparedness for such events. Although seasonal forecasts based on dynamical models are making inroads, statistical models based on sea surface temperature (SST) precursors are still widely used, making it important to better understand the strengths and weaknesses of such models. Here we define a simple statistical forecast model, which is used as a tool to shed light on the dynamics that link SSTs and rainfall across time and space, as well as on why such models sometimes fail. Our model is a linear regression, where the August states of El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) predict about 40% of the short rains variability in 1950–2020. The forecast errors are traced back to the initial SSTs: too-wet (too-dry) forecasts are linked linearly to positive (negative) initial ENSO and IOD states in August. The link to the initial IOD state is mediated by changes in the IOD between August and OND, highlighting a physical mechanism for prediction busts. We also identify asymmetry and nonlinearity: when ENSO and/or the IOD are positive in August, the range and variance of OND forecast errors are larger than when the SST indices are negative. Upfront adjustments of predictions conditional on initial SSTs would have helped in some years with large forecast busts, such as the dry 1987 season during a major El Niño, for which the model erroneously predicts copious rainfall, but it would have exacerbated the forecast in the wet 2019 season, when the IOD was strongly positive and the model predicts too-dry conditions. [ABSTRACT FROM AUTHOR]

It is well known that the Indian Ocean dipole (IOD) is closely related to El Niño-Southern Oscillation (ENSO). In this study, it is found that spring–summer north tropical Atlantic (NTA) sea surface temperature (SST) anomalies can contribute to the development of the IOD since the mid-1980s as well as ENSO. After the mid-1980s, an anticyclonic circulation over the subtropical northeastern Pacific could be excited by cool NTA SST anomalies in spring and summer due to a Gill-type Rossby-wave response. A low-level cyclonic circulation appears in the west Pacific in turn. The anomalous lower-level southwesterlies on the southeastern flank of the cyclonic circulation reduce the climatological wind speed, and thus, warm SST anomalies appear and extend to the central tropical Pacific via the wind-evaporation-SST (WES) feedback. As a result, Walker circulation over the Indo-Pacific region is changed, with anomalous descending in the eastern tropical Indian Ocean and ascending in the central tropical Pacific. The descending branch of anomalous Walker circulation generates surface southeasterly wind anomalies along the coast off Sumatra and lifts the thermocline in the eastern tropical Indian Ocean, which produces a positive IOD event in autumn. Such a cross-basin mechanism is supported by a coupled model experiment with warm SST perturbations over the NTA. In contrast, although cold NTA SST anomalies can induce warm SST anomalies in the eastern equatorial Pacific through interhemispheric meridional circulation before the mid-1980s, the responses in the tropical Indian Ocean are rather weak. In addition, the enhancement in the NTA-IOD relationship after the mid-1980s is suggested to result from the changes in the SST mean state under the context of global warming, which is confirmed by two coupled model experiments with different mean SST backgrounds. [ABSTRACT FROM AUTHOR]

To investigate the main modes of interannual variation of chlorophyll-a (Chla) with seasonal evolution and its variation cycle in the North Indian Ocean based on satellite-derived products during 1998–2016, a season-reliant empirical orthogonal function (S-EOF) analysis and power spectrum analysis based on Fourier transform are applied in the study. The first three dominate modes reveal distinct Chla variability, as the S-EOF1 features by one dipole pattern have a negative anomaly in the central western Indian Ocean and a positive anomaly off the Java–Sumatra coasts, which is mainly synchronously associated with the climate indices of the positive Indian Ocean dipole (IOD) and eastern Pacific El Nino (EP-El Niño). The S-EOF2 indicates a tripolar structure with positive anomalies located in the central Indian Ocean surrounded by two negative anomalies, which is one year behind a positive IOD and EP-El Niño event. The S-EOF3 exhibits a different dipole distribution, with a positive anomaly in the central west and a negative anomaly in the southeast, synchronized or lagging behind the central Pacific El Nino (CP-El Niño). Moreover, regarding the correlation between the main modes of interannual variation and the IOD and El Nino events, the dynamic parameters (such as SST, SLA, rain, and wind) of the tropical Indo-Pacific Ocean are discussed using time-delay correlation and linear regression analysis to explain the key factors and possible influencing mechanism of the joint seasonal and interannual variations of Chla in the northern Indian Ocean. [ABSTRACT FROM AUTHOR]

Coastal hypoxia—harmfully low levels of oxygen—is a mounting problem that jeopardizes coastal ecosystems and economies. The northern Indian Ocean is particularly susceptible due to human‐induced impacts, vast naturally occurring oxygen minimum zones, and strong variability associated with the seasonal monsoons and interannual Indian Ocean Dipole (IOD). We assess how natural factors influence the risk of coastal hypoxia by combining a large set of oxygen measurements with satellite observations to examine how the IOD amplifies or suppresses seasonal hypoxia tied to the Asian Monsoon. We show that on both seasonal and interannual timescales hypoxia is controlled by wind‐ and coastal Kelvin wave‐driven upwelling of oxygen‐poor waters onto the continental shelf and reinforcing biological feedbacks (increased subsurface oxygen demand). Seasonally, the risk of hypoxia is highest in the western Arabian Sea in summer/fall (71% probability of hypoxia). Major year‐to‐year impacts attributed to the IOD occur during positive phases along the eastern Bay of Bengal (EBoB), where the risk of coastal hypoxia increases from moderate to high in summer/fall (21%–46%) and winter/spring (31%–42%), and along the eastern Arabian Sea (i.e., India, Pakistan) where the risk drops from high to moderate in summer/fall (53%–34%). Strong effects are also seen in the EBoB during negative IOD phases, when the risk reduces from moderate to low year‐round (∼25% to ∼5%). This basin‐scale mapping of hypoxic risk is key to aid national and international efforts that monitor, forecast, and mitigate the impacts of hypoxia on coastal ecosystems and ecosystem services. Plain Language Summary: Coastal "dead zones," with vanishingly low oxygen levels, stress marine organisms, compress their habitats, threaten the sustainability of fisheries, and can lead to mass mortality of marine life. The northern Indian Ocean is particularly vulnerable due to natural physical processes that bring oxygen‐poor water onto the continental shelf from vast offshore regions of low‐oxygen, and biological processes that can intensify coastal dead zones. Alongside these natural processes, coastal dead zones in the Indian Ocean are also influenced by human activity, such as fertilizer use and waste water management. In this study we use a large set of observations in the northern Indian Ocean to quantify how natural processes trigger coastal dead zones seasonally, and how they increase or decrease the risk of coastal dead zones from year‐to‐year. This information, on where and when coastal dead zones are most likely to occur, is key to anticipate and mitigate impacts on ecosystems and economies. Key Points: Regions at higher risk of coastal hypoxia in the northern Indian Ocean are identified using coastal oxygen observationsThe Indian Ocean Dipole (IOD) can amplify or suppress the seasonal risk of hypoxia by modulating coastal upwelling/downwellingThe risk is most amplified during positive IOD phases along the coast of the eastern Bay of Bengal [ABSTRACT FROM AUTHOR]

A prominent subsurface upwelling over the Seychelles–Chagos Thermocline Ridge (SCTR) in the southwestern tropical Indian Ocean is suppressed when downwelling Rossby waves propagate from the eastern Indian Ocean during the positive phase of the Indian Ocean Dipole (IOD) or El Niño periods. Recent studies have suggested that the upwelling can be further suppressed during the co-occurrence years of positive IOD and El Niño, associated with the strong easterly wind anomalies in the eastern Indian Ocean. This study examines the temporal variations in the SCTR upwelling strength during 1968–2017, identifies strong upwelling suppression events, and analyzes their characteristics by focusing on the role of both remote and local wind forcing, not limited to the remote influence linked to the IOD and the El Niño Southern Oscillation. A total of nine events were identified for the 50-year period, with seven of them occurring 3–6 months after the co-occurring peaks of positive IOD and El Niño in the eastern Indian Ocean. However, only IOD exhibited a positive phase before the 2011–2012 suppression event associated with the downwelling-favorable anticlockwise local wind anomalies in the SCTR. Moreover, the 1978–1979 suppression event was primarily caused by the strong anticlockwise wind anomalies in the SCTR, without any significant influence of the positive IOD or El Niño. The results suggest that the role of local winds, as well as the remote forcing, are significant in the upwelling suppression over the SCTR, which would contribute to understanding the potential predictability of the upwelling variations. [ABSTRACT FROM AUTHOR]

El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) can reduce the amount of rainfall in Indonesia. The previous study found that ENSO and IOD derived from the OISST dataset have an association with hotspots in Indonesia, especially in southern Sumatra dan Kalimantan. But the correlation results are still too small, and the correlation strength between regions has not been analyzed. Therefore, this study quantifies the association of the estimated ENSO and IOD derived from the ERA5 dataset on hotspots in Indonesia based on a Heterogeneous Correlation Map (HCM) and analyzes the correlation strength between regions in Indonesia. We use a singular value decomposition method to quantify this HCM. Besides OISST, ERA5 is an estimation data often used for weather forecast analysis. Therefore, this study quantifies the association of the estimated ENSO and IOD derived from the ERA5 dataset on hotspots in Indonesia based on a Heterogeneous Correlation Map (HCM) and analyzes the correlation strength between regions in Indonesia. Based on variance explained and correlation strength, the hotspot in Indonesia is more sensitive to ENSO and IOD derived from ERA5 than OISST. Consequently, the ERA5 data more useful to statistical analysis that requiring a substantial correlation.

Indian Ocean Dipole (IOD) is the major interannual ocean-atmosphere interaction phenomena in the Indian Ocean (IO) and is influenced by external forcing such as El Nino Southern Oscillation (ENSO). Meanwhile, its co-occurrence and stronger relationship with ENSO have decreased during recent decades. The IOD variability also reduced after 2000, accompanied by a shift of the western pole to central IO extending further southward. The study reports that the boreal fall (SON, September, October, November) season IOD has an intensified relationship with the previous winter Subtropical Indian Ocean dipole (SIOD) and spring season equatorial north tropical Atlantic (NTA) SST anomalies., while the ENSO relationship is reduced from its pre-2000 value. It is found that the persistent warming (cooling) in the western side of positive (negative) SIOD during the previous winter induces easterly (westerly) wind anomalies in the equatorial IO during the following summer and fall, leading to positive (negative) IOD events. These IOD events have the western pole shifted to south-central IO instead of the canonical northwestern warming. The spring season NTA SST anomalies induce stronger summer season circulation and SST gradient in the equatorial Pacific, like ENSO. During the SON season, this pattern is associated with cooling and easterly wind anomalies in the tropical eastern IO and IOD. These two patterns explain the major mode of IOD variability after 2000. While the IOD associated with NTA have co-occurring ENSO during summer and fall, the SIOD-induced IOD events are independent of ENSO in the Pacific. Thus, these two predictors provide long-lead predictability (2–3 seasons ahead) of IOD for both ENSO co-occurring and non-ENSO IOD events. However, the IOD predictability of seasonal prediction models mainly depends on the ENSO-IOD relationship, resulting in reduced IOD skills for many of them after 2000. The models such as COLA-CCSM4, which has improved skill have stronger than observed ENSO-IOD relationship than the pre-2000 period. A linear regression model including SIOD and NTA SST indices of the previous winter and spring season respectively as predictors simulates IOD with a skill of around 0.65 during the recent period, indicating the necessity of seasonal prediction models to capture the variability in the southern IO and NTA and their teleconnections for better prediction of IOD in the recent period of reduced ENSO skill. [Display omitted] • ENSO predictability and ENSO-IOD relationship weakened in the recent decades. • Subtropical IOD in the previous winter strongly influence ENSO-independent IOD. • North tropical Atlantic SST in boreal spring induces IOD through Pacific modification. • Subtropical IOD and North Atlantic SST role in IOD is prominent after 2000. • A model with these two predictors induces IOD skill of above 0.65 at 2-3 seasons ahead. [ABSTRACT FROM AUTHOR]

A new framework of complex networks based on event synchronization that can be applied to the development of temperature anomalies associated with climate variation phenomena is developed to reveal propagation characteristics of ocean temperature anomalies and their asymmetry between positive and negative phases of the Indian Ocean Dipole (IOD). When a complex network based on sea surface temperature (SST) is constructed, it is revealed that SST anomalies in the eastern pole associated with both phases of the IOD tend to be preceded by those in the eastern equatorial region and from the south. When a complex network is constructed based on both surface and subsurface temperatures, it is found that the positive IOD tends to experience extreme subsurface temperature anomalies over more vast areas before extreme SST anomalies compared to the negative IOD. Plain Language Summary: The Indian Ocean Dipole (IOD) is an interannual climate phenomenon of the tropical Indian Ocean. During positive IOD events, anomalous cooling of sea surface temperature (SST) is observed in the southeastern tropical Indian Ocean, whereas anomalous warming occurs in the western tropical Indian Ocean. Anomalies with the opposite signs occur during negative IOD events. To investigate how such anomalous SST in the southeastern tropical Indian Ocean propagates during the IOD, a new framework of complex networks is proposed. When the complex network is constructed based only on SST, it is shown that both anomalously warm SST associated with the negative IOD and anomalously cool SST associated with the positive IOD tend to be preceded by those in the eastern equatorial region and to the south. When a complex network is constructed based on both surface and subsurface temperatures, it is found that the positive IOD tends to experience extreme subsurface temperature anomalies over more vast areas compared to the negative IOD. This suggests that the positive IOD may be more predictable than the negative IOD. Key Points: Complex network based on event synchronization is developed to examine temperature anomalies associated with the Indian Ocean Dipole (IOD)Sea surface temperature (SST) anomalies in the eastern pole tend to originate from the equator and to the south for both IOD phasesSST anomalies associated with the positive IOD tend to be preceded by subsurface temperature anomalies over more vast areas [ABSTRACT FROM AUTHOR]

With their complex narrow passages and vigorous mixing, the Indonesian seas provide the only low-latitude pathway between the Pacific and Indian Oceans and thus play an essential role in regulating Pacific-Indian Ocean exchange, regional air-sea interaction, and ultimately, global climate phenomena. While previous investigations using remote sensing and numerical simulations strongly suggest that this mixing is tidally driven, the impacts of monsoon and El Niño Southern Oscillation (ENSO) on tidal mixing in the Indonesian seas must play an important role. Here we use high-resolution sea surface temperature from June 2002 to June 2021 to reveal monsoon and ENSO modulations of mixing. The largest spring-neap (fortnightly) signals are found to be localized in the narrow passages/straits and sills, with more vigorous tidal mixing during the southeast (boreal summer) monsoon and El Niño than that during the northwest (boreal winter monsoon) and La Niña. Therefore, tidal mixing, which necessarily responds to seasonal and interannual changes in stratification, must also play a feedback role in regulating seasonal and interannual variability of water mass transformations and Indonesian throughflow. The findings have implications for longer-term variations and changes of Pacific–Indian ocean water mass transformation, circulation, and climate. [ABSTRACT FROM AUTHOR]

Twelve years of remotely sensed all-sat merged chlorophyll-a concentration unveils strong signatures of chlorophyll-a blooms along the south Java coast. An unprecedented three-times increase in chlorophyll-a concentration is significantly observed along the south Java coast during the southeast monsoon (June–October) than the northwest monsoon (December–April). The multiple regression analysis of dynamic factors evidently indicates that seasonal upwelling is predominantly controlled by the seasonally evolving coastal eddies associated with the seasonally reversing south Java coastal currents (SJCC) and Ekman mass transport (EMT), followed by the relative roles of sea surface temperature (SST) and wind stress curl. The eddy-induced upwelling and EMT-induced coastal upwelling lead to chlorophyll-a blooms during southeast monsoon, well-supported by the entrainment of cold and saline waters (thermocline doming) with low spiciness. On the other hand, the coastal eddies associated with SJCC and SST anomalies play a significant role in modulating the interannual surface chlorophyll-a variability in the domain. Intense chlorophyll-a blooms are observed during the positive IOD years, whereas the least chlorophyll-a concentration is observed during the negative IOD years. The unprecedentedly least chlorophyll-a concentrations during 2010 and 2016 are attributed to the intense and prolonged surface marine heatwaves. [ABSTRACT FROM AUTHOR]

We present a new assembly of three steppingstones in thorough inquiry of the complex chain reaction from the diverse equatorial sea surface temperature (SST) pattern two‐season ahead to the East Asia summer weather condition, by regarding the western North Pacific subtropical high (WNPSH) as an anchor. We identified three predictors that are discordant with conventional climatic indices and achieve a good skill in the summer WNPSH prediction (temporal correlation coefficient of 0.78) with a two‐season long lead in the leave‐1‐year‐out cross‐validation during 1981–2020, despite the diversity of El Niño‐Southern Oscillation (ENSO) and Indian ocean dipole (IOD) patterns. Specifically, the first predictor captures the initiation and development of both IOD and El Niño via the SST warming over central equatorial Pacific in autumn; the second one serves as a better delegate of IOD by capturing the easterly acceleration over tropical Indian ocean; the third one illustrates the unprecedented informative role of upper‐level high pressure over the entire tropics in the WNPSH prediction with 5months lead time. They mediate the discordance between conventional climate indices and the diverse WNPSH response and caution people to revisit and rethink the complex atmosphere‐ocean coupled response from the diverse tropical SST patterns two seasons ahead to EA summer weather condition. Plain Language Summary: To improve long‐lead prediction of East Asia (EA) summer weather conditions, we extract three steppingstones/signals in the thorough inquiry of complex air‐sea‐land coupling chain reaction from the diverse tropical oceanic conditions to the EA weather conditions. The first signal emphasizes the important role of the oceanic warming over central tropical Pacific in autumn in the western North Pacific subtropical high (WNPSH) prediction, offering more information than the traditional signals over the eastern tropical Pacific in winter (e.g., Niño 3.4). The second signal extracts the easterly acceleration to better represent the Indian ocean dipole pattern instead of the conventional sea surface temperature‐based index. The third signal, which captures the intensification of upper‐level high pressure over entire tropics, provides surprisingly informative predictability of WNPSH from 5months ahead. Three signals defeat the conventional climatic indices and achieve promisingly high skill in the prediction of a major driver of EA weather conditions (i.e., WNPSH) with a two‐season long lead (temporal correlation coefficient of 0.78). The discordance between the three signals and conventional climate indices cautions people to rethink and revisit the complex air‐sea‐land coupling system and provide new metrics for climate model validation and elucidating the future impact of tropical oceanic conditions under anthropogenic warming. Key Points: Three signals outperform the conventional indices with a good two‐season‐ahead predictive skill in western North Pacific subtropical highWarming intensified over selected central Pacific region in fall captures the initiation and development of El Niño and Indian ocean dipoleEasterly acceleration is a delegate of Indian ocean dipole, and intensification of upper‐level high pressure is found informative [ABSTRACT FROM AUTHOR]

The Indian Ocean Dipole (IOD) is recognised as an important driver of interannual climate variability over different regions of the globe, including the regional monsoon systems. In particular, positive (negative) phases of IOD tend to be associated with above-normal (below-normal) monsoon rainfall over the Indian subcontinent. Realistic simulation of the IOD and Indian summer monsoon connection, however, remains a challenge in many of the state-of-the-art climate models. This study presents an analysis of IOD and its links to the Indian monsoon based on the historical simulations from the IITM Earth System Model (IITM-ESM) and other models that participated in the 6th phase of Coupled Model Intercomparison Project (CMIP6). Our findings indicate that the IITM-ESM provides not only a fairly realistic simulation of the ocean–atmosphere coupled interactions and the Bjerknes feedback processes associated with IOD events but also better captures the summer monsoon precipitation response over the Indian subcontinent during IOD events, as compared to several CMIP6 models. The physical mechanisms contributing to the improved simulation of IOD and its monsoon connection in the IITM-ESM are evaluated in this study. [ABSTRACT FROM AUTHOR]

Precipitation extremes will generally intensify in response to a warming climate. This robust fingerprint of climate change is of particular concern, resulting in heavy rainfall and devastating floods. Often this intensification is explained as a consequence of the Clausius–Clapeyron law in a warmer world, under constant relative humidity. Here, based on an ensemble of CMIP5 global climate models and high-resolution regional climate simulations, we take the example of Southwest Asia, where extreme storms will intensify beyond the Clausius- Clapeyron scaling, and propose an additional novel mechanism for this region: the unique increase in atmospheric relative humidity over the Arabian Sea and associated deep northward penetration of moisture. This increase in humidity is dictated by changes in circulation over the Indian Ocean. Our proposed mechanism is consistent with the recent, most extreme storm ever observed in the region. Our findings advance a new understanding of natural climate variability in this region, with substantial implications for climate change adaptation of the region's critical infrastructure. [ABSTRACT FROM AUTHOR]

In this study, we performed a long‐term ensemble hindcast from 1880 to 2017 (138 years) using the Community Earth System Model (CESM) and conducted a comprehensive investigation of the Indian Ocean Dipole (IOD) predictability. We found that the CESM can produce the IOD prediction skill comparable to that produced by some of the best state‐of‐the‐art coupled general circulation models, achieving a correlation skill of 0.5 for a lead time of one season over the 138 years. The Brier skill score shows one season of the effective probability prediction skill for the below‐ and above‐normal events and no probability prediction skill for the near‐normal events. The potential predictability of the IOD is much higher than the actual prediction skill; for example, the information‐based potential correlation is as high as 0.8 at a 6‐month lead time, suggesting a large scope for improvement in current IOD predictions. Compared with the dispersion component, the signal component dominates the variation in the relative entropy and the relationship between the potential predictability and deterministic prediction skill. An analysis of the IOD prediction skills suggests that the strength of IOD events plays an important role in the IOD prediction skills, regardless of the measurement metrics used to evaluate the prediction skills. Our study also suggested that the remote forcing from the tropical Pacific and the local sea‐air interaction in the tropical Indian Ocean would be two major sources of IOD predictability. Plain Language Summary: The Indian Ocean dipole (IOD) has large impacts on the worldwide climate anomalies. Previous investigations of the IOD predictability either used hindcasts covering only a few decades or employed intermediate coupled models. In this study, we use the Community Earth System Model to conduct a 138‐year (1880–2017) ensemble hindcast. It is the first time to investigate the IOD deterministic and probability skill as well as its potential predictability using such a long‐term hindcast period. Many important findings and conclusions are derived including the robust features of IOD predictability and its dominant factors. This study deepens our understanding of IOD predictability, and is theoretically significant to promote the study of IOD predictability. Key Points: A long‐term ensemble hindcast for 138 years was conducted using the Community Earth System ModelThe IOD predictability, including the deterministic and probability prediction skills, as well as the potential prediction, is investigatedThe strength of IOD events plays an important role in the IOD prediction skills, regardless of the measurement metrics [ABSTRACT FROM AUTHOR]

The coastal area of Java has become a centre of new economic growth. The southern coast of Java, which is directly adjacent to the tropical Indian Ocean, is very vulnerable to sea level rise caused by climate change. Information on variability and trends in sea level are therefore very important for adaptation and disaster mitigation efforts. This research was conducted to determine the variability and trend of sea level in the southern sea of Java. Data used were from satellite altimeter from 1993 to 2018 and tide gauges from 2007 to 2015. The rate of sea level rise was analysed using linear regression. The results showed that the sea level variability in the southern waters of Java was influenced by the Asian–Australian monsoon, eddy currents and the Indian Ocean Dipole (IOD). During June–November, there was a very significant decrease in sea level, especially in the south of East Java and Central Java, which was caused by upwelling and eddy currents. When there was a positive phase of IOD and an El Niño event, sea level decreased; conversely, when the IOD was in a negative phase, sea level increased. For the period 1993–2018, the sea level in the southern waters of Java increased by about 4.7 mm/year.

The IOD can be measured using the Dipole Mode Index (DMI) which is calculated based on the sea surface temperature in the Indian Ocean. Therefore, DMI can be predicted using sea surface temperature forecasting data, such as data provided by the European Center for Medium-Range Weather Forecasts (ECMWF). However, the data still has a bias as compared to the actual data, so to get a more accurate prediction, corrected data is needed. Therefore, the aim of this study is to predict DMI based on sea surface temperature forecasting data that has been corrected for bias using the quantile mapping method, a method that connects the distribution of forecasting and actual data. The results showed that the DMI prediction using corrected data was more accurate than the DMI prediction using ECMWF data. DMI predictions using corrected data have high accuracy to predict IOD events in October-April.

This study investigated the interannual variability of yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) catches in the southwestern tropical Indian Ocean (SWTIO) over 25 years and its relationship to climate variability. The results indicate that the catch amount in the northern SWTIO exhibits a significant relationship with the temperature, salinity, and current variability in the upper ocean (< 400 m), associated with a significant subsurface upwelling variability, which is prominent only in the northern region. An increase of the tuna catches in the northern region is associated with the deepening of the thermocline depth and 20°C isotherm depth of the Seychelles–Chagos Thermocline Ridge, indicating suppression of the subsurface upwelling. Further analysis reveals that the catch amounts in the SWTIO tend to increase during the positive phase of the Indian Ocean Dipole. However, the catch variability in the northern SWTIO is more closely related to the El Niño–Southern Oscillation than the Indian Ocean Dipole. Favorable conditions for catches seem to develop in the northern region during El Niño years and continue throughout the following years. This relationship suggests the potential predictability of catch amounts in the northern SWTIO, an energetic region with strong subsurface upwelling variability.

The superparameterized Community Atmosphere Model (SPCAM) is used to investigate the impact and geographic sensitivity of positive Indian Ocean Dipole (+IOD) sea-surface temperatures (SSTs) on Madden-Julian oscillation (MJO) propagation. The goal is to clarify potentially appreciable +IOD effects on MJO dynamics detected in prior studies by using a global model with explicit convection representation. Prescribed climatological October SSTs and variants of the SST distribution from October 2006, a +IOD event, force the model. Modest MJO convection weakening over the Maritime Continent occurs when either climatological SSTs, or +IOD SST anomalies restricted to the Indian Ocean, are applied. However, severe MJO weakening occurs when either +IOD SST anomalies are applied globally or restricted to the equatorial Pacific. MJO disruption is associated with time-mean changes in the zonal wind profile and lower moist static energy (MSE) in subsiding air masses imported from the Subtropics by Rossby-like gyres. On intraseasonal scales, MJO disruption arises from significantly smaller MSE accumulation, weaker meridional advective moistening, and overactive submonthly eddies that mix drier subtropical air into the path of MJO convection. These results (1) demonstrate that SPCAM reproduces observed time-mean and intraseasonal changes during +IOD episodes, (2) reaffirm the role that submonthly eddies play in MJO propagation and show that such multiscale interactions are sensitive to interannual SST states, and (3) suggest that boreal fall +IOD SSTs local to the Indian Ocean have a significantly smaller impact on Maritime Continent MJO propagation compared to contemporaneous Pacific SST anomalies which, for October 2006, resemble El Ninõ-like conditions.

High resolution mean surface velocity field of the Arabian Sea was derived by combining sea level anomalies based on satellite altimetry data with the surface drifter data. The mean current field exhibits the western boundary Somali Current, weak westward North Equatorial Current, weak West Indian Coastal Current. Besides strong currents, the Arabian Sea exhibits strong mesoscale eddy activity in the western side. The seasonal surface circulation changes of the Arabian Sea and variability associated with the Indian Ocean Dipole (IOD) events were determined. The Somali Current is northward during summer, with a speed above 1.8 m/s in July and it reverses towards south in winter. Significant changes were found in the flow pattern during IOD events. An anticyclonic gyre near the equator was a conspicuous feature during the positive IOD. Further, the Great Whirl shows an earlier formation and dissipation during the positive IOD. Notably, a delay of southward reversal of the Somali Current is found during the positive IOD. The southward flow of West Indian Coastal Current during summer monsoon is much stronger during the positive IOD and the northward flow in fall is prominent during negative IOD. The eastward Equatorial Jet is absent in fall and instead an opposite (westward) flow prevails during the positive IOD. Enhanced Chl-a concentration occurs during the negative IOD, compared to the positive IOD, especially in the western Arabian Sea. The wind-driven upwelling and mesoscale eddies are significantly modifying the Chl-a distribution along the Somali Coast.Highlight: A high resolution mean surface velocity field is developed. Contrasting circulation changes are found during positive and negative IOD events. Mesoscale eddy activity is considerably influencing the Chlorophyll distribution. [ABSTRACT FROM AUTHOR]

This study examined the predictive skill of a statistical Generalised Additive Model (GAM) by considering the impact of the Indian Ocean Dipole (IOD). The proposed technique is powerful but simple and considers both the linear and non-linear relations hidden in the data. The model considers tropical cyclogenesis through kernel density estimation, trajectories by velocity field, and landfall through a country mask approach. A lead–lag analysis for TC forecast potential confirms that the IOD is a good predictor for 2-month lead forecast. Result shows that TC occurrence increase (decrease) during the negative (positive) IOD events and that the landfall probability vary for each IOD phase. Altering convection, steering flow, and low-level vorticity influence the NIO TC activity. Result also highlights the importance and potential of the GAM approach (approximately 72% skill) in matching predicted landfall with the observations. [ABSTRACT FROM AUTHOR]