Indian Ocean Dipole Mode Research Articles

ENSO and QBO Controls the Favorableness of the MJO Realization Cooperatively

AbstractWe examine a mechanism of the interannual variability of the realization frequency of the Madden‐Julian oscillation (MJO). The activity of boreal‐winter MJO realization is quantified by the number of MJO active days during the tracking of the real‐time multivariate MJO index. In active years of MJO realization (MJO‐A), multiple MJOs are initiated in the Indian Ocean (IO) and they propagate into the western Pacific (WP), but not so in inactive years (MJO‐IA). This contrast is explained by whether vertical moisture advection over the WP is disrupted or not. It is related to differences in boreal‐winter mean convection and circulations: MJO‐A (MJO‐IA) years are characterized by enhanced and suppressed (suppressed and enhanced) convection over the WP/IO and Maritime Continent (MC), respectively. This modulation results from combined effects of the El Niño‐Southern oscillation (ENSO) and quasi‐biennial oscillation (QBO). During moderate‐to‐strong El Niño, MJO is realized actively irrespective of QBO, if no additional convective suppression over the eastern IO and/or MC due to other forcing such as a positive Indian Ocean Dipole mode. During other ENSO phases, stronger QBO‐easterly phases favor MJO realization irrespective of ENSO. This QBO–MJO connection except for El Niño conditions is due to zonally heterogeneous QBO impacts that the seasonal mean static stability change near the tropopause over the WP alters the mean convective activity there. This zonal heterogeneity and ENSO phase‐dependency of QBO impacts is interpreted with a focus on vertical propagation of Kelvin wave structure over the MC, affected by both QBO winds and background Walker circulations.

Extreme droughts in the Amazon Basin during cyclic ENSO events coupled with Indian Ocean Dipole modes and Tropical North Atlantic warming.

The teleconnections between El Niño-Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), and Tropical North Atlantic warming (+TNA) play a critical role in characterizing extreme drought events in the Amazon Basin (AB). This study examines the seven most recent drought extreme events up to 2023, using seasonal composites of the sea surface temperature and atmospheric variables over a five-quarter period starting at the austral spring(-1) of the year preceding that when the lowest water level at Manaus port was recorded. Two distinct patterns emerge, driven by consecutive ENSO events with opposite phases, referred to as cyclic La Niña-El Niño and cyclic El Niño-La Niña drought events. For these events, IOD and ENSO modes are coupled in the same phase during the springs, with ENSO triggering and enhancing IOD, and the IOD, in turn, enhancing and sustaining ENSO through Walker circulation. This interaction can amplify extratropical Rossby waves in both hemispheres, originating from the equatorial Indian and Pacific Oceans. Notably, strong positive ENSO and IOD phases trigger or sustain the +TNA by weakening northeasterlies through a Pacific-North America wave train. The IOD, ENSO and +TNA, individually or combined, influence atmospheric circulation patterns over South America through Rossby waves and anomalous Walker and Hadley circulation patterns, causing dry periods in the AB marked by negative precipitation anomalies across specific regions or the entire AB, consequently modulating the water levels at Manaus. The strong coupling of these three tropical modes is crucial to leading multiyear drought events in the AB. This study underscores the potential for a robust climate forecasting system by monitoring the oceanic indices.

A Study of the Correlation between ElNiño-Southern Oscillation and Indian Ocean Dipole Mode Indices, and Korean Drought Indices

The correlation between ocean climate and Korean drought indices is key in explaining and predicting droughts in Korea. In this study, ocean climate index data, including El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) index values, were subjected to a Pearson correlation analysis with standardized precipitation index (SPI) data. The results of the analysis show that the SPI and ocean climate change are linked, which provides a possible explanation for the effect of ENSO and IOD on drought in Korea. However, because the magnitude of the observed link was not very large, the correlations ENSO and IOD indices, respectively, and SPI are statistically weak. On analysis of monthly data, significant correlations were mainly observed from January to May, with very weak correlations from June to December. Based on a regional analysis, twelve cities were divided into four groups with similar correlations between the analyzed indices.

Impact of the Indian Ocean Dipole Mode on Planetary Boundary Layer Ozone in China

AbstractThe Indian Ocean Dipole (IOD) mode exerts distinct impacts on the climate in China and can further affect tropospheric ozone. Using long‐term GEOS‐Chem simulations, we found distinct changes in planetary boundary layer ozone throughout China during positive and negative phases of IOD. In summer, ozone shows synchronized increases except in southern China during positive IOD; the ozone increases are dominated by chemical production and transport in northern and western China, respectively. The increased precursor from biogenic emissions contributed to ozone chemical formation in the northern region, and the increased precipitation and decreased solar radiation hindered ozone production in southern China. Ozone changes show good symmetry over most regions during negative IOD. In autumn, the ozone reduction in southern China shares the same reason as summer, while the chemical increase over northern China is affected more by changes in solar radiation and relative humidity than in the precursor emission.

The 2019–21 drought in southern Madagascar

Two consecutive failed rainy seasons in the southern part of Madagascar in 2019–21 had devastating impacts on the population, including an amplification of the ongoing food insecurity in the area. The drought events were second in severity only to the 1990–92 drought and were estimated in a previous study to have a return period of 135 years. In this study, the physical mechanisms that led to these consecutive drought events are investigated.We found that the anomalously cold sea surface temperatures (SSTs) that persisted to the south of Madagascar between December 2019 and December 2020 led to a decrease in the transport of moist air over land. These cold SST anomalies were the most negative anomalies in the past four decades and intensified the rainfall deficit resulting from a negative Subtropical Indian Ocean Dipole (SIOD) mode during the rainy season of December 2019 to March 2020 and during December 2020. We also found that the rainfall response to the SST anomaly south of Madagascar was three times greater than that of a canonical SIOD.A weak Mozambique Channel Trough and a strong Angola low system, on the other hand, modulated the expected above-normal rainfall from a La Niña event in January–February 2021. Our study demonstrates how local factors can modulate the impacts of large-scale drivers, and that both local and global drivers, and their interactions, should be considered when producing seasonal forecasts and advisories, as well as climate change adaptation and mitigation plans for southern Madagascar.

Intraseasonal Variations and Extreme Occurrence in the Local Sea Level Along the Western Coast of India Remotely Controlled by a Basin‐Scale Climate Variability

AbstractThe equatorial Kelvin waves, remotely excited by basin‐scale climate modes, and subsequent coastal trapped waves significantly influence the intraseasonal variations, their low‐frequency modulations, and the frequency of extreme sea level events along the western coast of India. This study demonstrates that the frequency of extreme events are linked to the phase of the Indian Ocean Dipole mode. The temporal changes in the occurrence frequency of extremes are simulated in an eddy‐resolving ocean model consistently with observations. However, a non‐eddying model significantly underestimate the occurrence frequency of extreme sea level events, suggesting the importance of coastal trapped wave propagations regulated by the horizontal scale with the Rossby radius of deformation. This result implies that many state‐of‐the‐art climate models with a one‐degree ocean horizontal resolution may underestimate future coastal sea level variability and the frequency of extreme events under global warming and potential modulations of major internal climate modes.

Climatic influence of the Antarctic ozone hole on the East Asian winter precipitation

The Antarctic ozone hole exerts a substantial impact on the climate of the Southern Hemisphere, yet research exploring its potential influence on the Northern Hemisphere climate is limited. This study unveils a significant positive relationship between interannual variations of Antarctic total column ozone (TCO) during September–October and East Asian precipitation in the subsequent boreal winter. Specifically, ~10% of the East Asian winter precipitation variability is attributed to Antarctic TCO during September–October. Both observational data and model results indicate that the increased Antarctic TCO during September–October triggers a simultaneous meridional southern Indian Ocean tripole sea surface temperature anomalies (SSTA) through the negative phase of the Southern Annular Mode. This SSTA pattern persists from September–November through the boreal winter, subsequently weakening the local-scale zonal-vertical circulation anomalies in the Indian Ocean. The process leads to positive outgoing longwave radiation (OLR) anomalies over the southern Marine Continent. As a result, the linear response of wind anomalies at 850 hPa over East Asia to the OLR-induced diabatic heating anomalies exhibits southwesterlies, as demonstrated by a linear baroclinic model. These anomalous winds facilitate the transport of abundant moisture from the tropics to East Asia, favoring the formation of winter precipitation. We employ the Specified-Chemistry version of the Whole Atmosphere Community Climate Model to validate that the increase of September–October Antarctic ozone substantially enhances East Asian precipitation during boreal winter. Importantly, the relationship between Antarctic ozone and East Asian winter precipitation is found to be independent of El Niño-Southern Oscillation and the Indian Ocean Dipole Mode. Our findings provide a fresh insight into the prediction of the East Asian winter precipitation.

What Determines the East Asian Winter Temperature during El Niño?—Role of the Early Onset El Niño and Tropical Indian Ocean Warming

Abstract Atmospheric teleconnections from the Pacific El Niño are key to determining the East Asian winter climate. Using the database for policy decision-making for future climate change (d4PDF) large-ensemble simulations, the present study investigates a mechanism for the warm and cold East Asian winters during El Niño with a focus on atmospheric teleconnections triggered by anomalous sea surface temperature (SST) patterns in the tropical Indo-Pacific. Our results show that the western Pacific (WP) teleconnection pattern plays a primary role in the warm winters in East Asia. The WP pattern tends to appear in years when both an early El Niño and the positive phase of the Indian Ocean dipole (IOD) mode develop in boreal autumn. In those years, the tropical Indian Ocean (TIO) strongly warms in the following winter, forming a distinct zonal contrast in precipitation anomalies over the tropical Indo-Pacific through a reduced Walker circulation. The Rossby wave source anomalies indicate that the WP pattern is associated with the weakened Indo-Pacific Walker circulation. By contrast, the WP pattern does not dominate in the cold winters due to the absence of strong TIO warming. The present study proposes a mechanism that promotes the excitation of the WP pattern through the upper-troposphere divergence in East Asia associated with the Walker circulation modulated by the tropical Indo-Pacific interbasin interaction. Significance Statement The East Asian winter temperature variability is controlled not only by the strong atmospheric internal variability in the midlatitudes and high latitudes but also by remote forcing from the tropical ocean. Our study investigates how El Niño exerts diverse impacts on the East Asian winter temperature, depending on where atmospheric convection intensifies in the tropical Pacific Ocean and the Indian Ocean. Our results show that an intense warming of the tropical Indian Ocean and the early development of El Niño are the major factors for warm winters in East Asia. Given that a precursor of the intense Indian Ocean warming appears in boreal autumn, our findings should contribute to the improvement of seasonal prediction for the East Asian winter climate.

Variability of rainy season onsets over East Africa

AbstractOver the East Africa region forecasts of the onset of the rainy seasons have the potential to support decision‐making, especially in the largely rain‐fed agricultural sector. However, the understanding of key features of onset remains limited. Here, we analyse the variability of onset and associated drivers at interannual and subseasonal timescales, using several onset definitions. Results show that the onset date is especially variable from year to year in some of the high‐potential agricultural areas (standard deviation >20 days), which has implications for agricultural risk management. The choice of onset definition metric matters; agronomic definitions have limited applicability at the regional scale and are also highly sensitive to the spatial scale of analysis and to the choice of rainfall data. Onset information provided at coarse scales should be used with caution for decision‐making at the local scale; the “hit rate” of coarse‐scale tercile onset information at the local scale is less than 40% on average. To varying degrees, onset is related to total seasonal rainfall and thus to dominant interannual drivers of rainfall, including the Indian Ocean Dipole and ENSO modes in October–December and the western Pacific “V‐gradient” pattern in March–May. However, by analysing the dominant proportion of onset variance unrelated to total rainfall during the climatological season we show a substantial influence of subseasonal drivers, notably the Madden–Julian Oscillation. As such, there is an opportunity for rainfall onset information to be provided across seasonal and subseasonal timescales. Our work reinforces the need for enhanced co‐production of such onset information with stakeholders, especially regarding the choice of metric, alignment of forecasts with livelihood calendars, interpretation of the credibility of information content for local‐level decision‐making, as well as appropriate strategies for staggered risk management interventions informed by forecasts over “seamless” lead times.

Asymmetric El Niño–Southern Oscillation and tropical cyclone relationships in the Philippines during October–December

AbstractThis study demonstrates asymmetric relationships between El Niño–Southern Oscillation (ENSO) and tropical cyclones (TCs) affecting the Philippines during October–December. In El Niño or La Niña years, the number of TCs impacting the Philippines may increase or decrease. These variations result in four ENSO–TC variability types all of which exhibit strong sea surface temperature (SST) anomalies across the equatorial eastern Pacific. The major difference between the active and inactive types in terms of El Niño or La Niña years is related to the magnitude of SST anomalies in the tropical western Pacific (TWP) over the 120°–150°E region. During El Niño years, moderate cold SST anomalies in this TWP region cause an anomalous divergent centre around the 120°–130°E zone to evoke an anomalous cyclone east of the Philippines. In the western North Pacific (WNP), this anomalous cyclone causes more TCs to form and move toward the Philippines, resulting in active TC activity. For the inactive TC type during El Niño years, very weak cold SST anomalies in the aforementioned TWP region correspond with a northeastward‐extended anomalous divergent centre over the 120°–140°E, 10°S–20°N zone and an anomalous anticyclone across the Philippines and its eastern side. Decreases in the formation of the WNP TC and movement toward the Philippines lead to inactive TC activity. The large‐scale anomalies and regulating processes are mainly opposite between the active TC type during El Niño years and the inactive TC type during La Niña years. These two types are influenced by interdecadal variability of the Pacific decadal oscillation. Opposite anomalies and regulating processes also occur between the inactive TC type during El Niño years and the active TC type during La Niña years. The former type is jointly modulated by the positive Indian Ocean Dipole mode and central‐Pacific El Niño.

The dominant influence of indian ocean dipole-like ocean warming on decreased precipitation over eastern East Antarctica

East Antarctica is undergoing a noticeable decrease in precipitation, significantly impacting ice mass loss. However, there is a lack of research on the underlying factors behind this change. This study highlights that on an interannual timescale, the precipitation variations in Eastern East Antarctica (EEA) are predominantly influenced by the Indian Ocean Dipole mode (IOD) compared to other climate variabilities like the Southern Annular Mode (SAM), El Niño–Southern Oscillation (ENSO), and north Atlantic variability. Through trend analysis of each climate variability, we confirmed that the observed decrease in EEA precipitation can be attributed to positive IOD-like ocean warming. A positive SAM trend also contributed to specific Wilkes Land and Queen Mary Land regions. Despite these influence on long-term trend, the relationship between IOD and EEA precipitation exhibits sporadic changes on interdecadal timescales. Notably, the apparent negative correlation between the two declined to insignificance in the early 2000s, only to re-establish a significant negative correlation by the early 2010s. The primary driver of this change is the inconsistent propagation of waves originating from the Indian Ocean. During periods of high correlation, these waves propagate southeastward, inducing a robust low-pressure anomaly near Victoria Land, ultimately leading to decreased EEA precipitation. However, during periods of low correlation, the waves move eastward and fail to alter the circulation anomalies near East Antarctica.

Unraveling sub-seasonal precipitation variability in the Middle East via Indian Ocean sea surface temperature

This study examines sub-seasonal precipitation anomalies, challenging to predict yet vital for society and the environment. Focusing on October, we investigate correlations between the Indian Ocean Dipole Mode Index (DMI), West Tropical Indian Ocean Index (WTIO), and Middle Eastern precipitation. We find robust correlations (~ 0.7), up to a two-month lag, demonstrating strong links between these climate indices and rainfall patterns, potentially suggesting sub-seasonal precipitation predictability. Over the past four decades, DMI and WTIO have shown a significant upward trend of ~ 0.4 °C, intensifying their impact on precipitation dynamics. This trend signifies evolving Indian Ocean climate patterns with potential regional consequences and is projected to continue in the twenty-first century. Significant correlations also emerge between DMI, WTIO, and maximum daily precipitation, highlighting their role in extreme rainfall events. Finally, our study attributes most of October’s precipitation variability to Indian Ocean sea surface temperature variations. These temperature anomalies influence the Indian Ocean’s Walker circulation, affecting water vapor flux to the Middle East and shaping regional precipitation. Our findings underscore the importance of these indices in understanding and predicting Middle East climate variability, revealing intricate ocean–atmosphere interactions.

Attributing interdecadal variations of southern tropical Indian Ocean dipole mode to rhythms of Bjerknes feedback intensity

Attributing interdecadal variations of southern tropical Indian Ocean dipole mode to rhythms of Bjerknes feedback intensity

Boosting effect of strong western pole of the Indian Ocean Dipole on the decay of El Niño events

The Indian Ocean Basin (IOB) mode is believed to favor the decay of El Niño via modulating the zonal wind anomalies in the western equatorial Pacific, while the contribution of the Indian Ocean Dipole (IOD) mode to the following year’s El Niño remains highly controversial. In this study, we use the evolution of fast and slow decaying El Niño events during 1950–2020 to demonstrate that the positive IOD with a strong western pole prompts the termination of El Niño, whereas a weak western pole has no significant effect. The strong western pole of a positive IOD leads to a strong IOB pattern peaking in the late winter (earlier than normal), enhancing local convection and causing anomalous rising motions over the tropical Indian Ocean and sinking motions over the western tropical Pacific. The surface equatorial easterly wind anomalies on the western flank of the sinking motions stimulate oceanic equatorial upwelling Kelvin waves, which shoal the thermocline in the eastern equatorial Pacific and rapidly terminate the equatorial warming during El Niño. However, a weak western pole of the IOD induces a weak IOB mode that peaks in the late spring, and the above-mentioned cross-basin physical processes do not occur.

The Indian Ocean Weakens the ENSO Spring Predictability Barrier: Role of the Indian Ocean Basin and Dipole Modes

Abstract Prediction of El Niño–Southern Oscillation (ENSO) is hindered by a spring predictability barrier (SPB). In this paper, we investigate the effects of the Indian Ocean (IO) on the SPB. Using a seasonally varying extended IO–ENSO recharge oscillator model, we find that the SPB is much weakened when IO is coupled with ENSO. To gauge the relative role of the Indian Ocean dipole (IOD) and the Indian Ocean Basin (IOB) modes in weakening ENSO SPB, we develop an empirical dynamical model, the linear inverse model (LIM). By coupling/decoupling the IOB or IOD mode with ENSO, we show that the IOB significantly weakens eastern Pacific and central Pacific ENSO SPBs, while the IOD plays a weaker role. The evolution of the optimum initial structures also illustrates the importance of the IOB in ENSO SPB. Moreover, the IOB strongly influences the forecast skill of La Niña SPB rather than El Niño SPB. This point is also identified through six coupled models from the North American multimodel ensemble. It may be related to the role of the IO in the asymmetry in the duration of El Niño and La Niña. The IOB-induced easterly wind anomalies are conducive to the development of La Niña and thus the prediction of La Niña events, whereas these anomalous easterlies are less important during the development of El Niño and the related forecast of El Niño events.

Diagnosing Seasonal Forecast Skill of the Indian Ocean Dipole Mode Using Model Analogs

Abstract A retrospective tropical Indian Ocean dipole mode (IOD) hindcast for 1958–2014 was conducted using 20 models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), with a model-based analog forecast (MAF) method. In the MAF approach, forecast ensembles are extracted from preexisting model simulations by finding the states that initially best match an observed anomaly and tracking their subsequent evolution, with no additional model integrations. By optimizing the key factors in the MAF method, we suggest that the optimal domain for the analog criteria should be concentrated in the tropical Indian Ocean region for IOD predictions. Including external forcing trends improves the skills of the east and west poles of the IOD, but not the IOD prediction itself. The MAF IOD prediction showed comparable skills to the assimilation-initialized hindcast, with skillful predictions corresponding to a 4- and 3-month lead, respectively. The IOD forecast skill had significant decadal variations during the 55-yr period, with low skill after the early 2000s and before 1985 and high skill during 1985–2000. This work offers a computational efficient and practical approach for seasonal prediction of the tropical Indian Ocean sea surface temperature.

Multi-decadal enhancement in the influence of El Niño on the Indian Ocean dipole mode

Multi-decadal enhancement in the influence of El Niño on the Indian Ocean dipole mode

Summertime discontinuity of Western Boundary Current in the Bay of Bengal during contrasting Indian Ocean Dipole events of 2008 and 2010

The East India Coastal Current (EICC), the Western Boundary Current (WBC) in the Bay of Bengal (BOB) is continuous northward and southward during pre- and post-Indian Summer Monsoon (ISM), respectively. The discontinuity in EICC occurs during ISM (June–September) when the boundary current remains inconsistent with various cyclonic and anticyclonic eddies in presence of a southward flow from 21°N and a northward flow from 10°N along the boundary. The variations in this summertime EICC discontinuity during the contrasting Indian Ocean Dipole (IOD) events of 2008 (positive) and 2010 (negative) are investigated here. The study uses a 1/12° Regional Ocean Modelling System (ROMS) simulation, available observations and reanalysis data. The study reveals that the strong coastal Kelvin and reflected Rossby waves during 2010, supported by strong winds in the equatorial Indian Ocean, helped to strengthen the spring and winter time continuous EICC. The continuous EICC remained very weak with the weaker equatorial remote forcing signals in 2008. The southward and northward flows from 21°N and 10°N, respectively were much stronger during 2010 ISM. However, strong eddy activities along the boundary reduced these two flows in 2008. The year 2010 showed relatively weak, but well-distributed eddy activity over the whole western BOB during ISM. Conversely, pronounced eddy activity near the western boundary with high eddy kinetic energy accumulation increases the inconsistency in boundary current flow during ISM of 2008. Therefore, the study suggests that the contrasting IOD modes have significant and complementary influence on WBC discontinuity in the BOB.

Improved Predictability of Summertime Rossby Wave Breaking Frequency near Japan in JMA/MRI-CPS3 Seasonal Forecasts

Abstract The seasonal predictability of the Rossby wave breaking (RWB) frequency near Japan in July–August (JA) is examined using daily JMA/MRI-CPS3 (CPS3) hindcast data, which is an operational seasonal prediction system of the Japan Meteorological Agency. Although the RWB frequency near Japan during JA in CPS3 is underestimated in comparison with the reanalysis, interannual variabilities of the frequency are generally predicted with moderate or high skill for hindcasts, initiating from February to June. The RWB frequency forecast skill in CPS3 is much higher than that in the previous version of the seasonal prediction system due to the improvement in the model bias of the Asian jet stream meridional position. A regression analysis for the RWB frequency near Japan utilizing all ensemble members is conducted to evaluate the reproducibility of the increased (decreased) RWB frequency associated with La Niña (El Niño) conditions, as indicated by previous studies. The regressed anomalies demonstrate an anomalous sea surface temperature (SST) pattern similar to that of La Niña and a negative phase of the Indian Ocean dipole mode with the associated anomalous convection in the tropics. For the La Niña condition, the regressed geopotential height in the upper troposphere demonstrates negative anomalies over the tropical Pacific and positive anomalies in the extratropical Northern Hemisphere, corresponding to the enhanced mid-Pacific trough and northward-shifted subtropical jet. The regressed meridional wind anomalies demonstrate a wavy pattern along the Asian jet over Eurasia, consistent with the relationship between the Silk Road pattern and the RWB near the Asian jet exit region.

Phase Shift of the Winter South China Sea Western Boundary Current Over the Past Two Decades and Its Drivers

AbstractThe winter South China Sea (SCS) western boundary current (WBC) has presented a significant weak–strong–weak phase shift in the last two decades, as revealed by observations and model products. Its phase shift has mainly been attributed to the joint effect of wind stress curl over the SCS and Luzon Strait transport (LST). Changes in the wind stress curl and planetary vorticity input through the Luzon Strait are the two major sources maintaining the winter SCS WBC state in different phases. The LST is closely related to the Kuroshio strength and thus the Pacific North Equatorial Current (NEC) bifurcation. Therefore, the winter SCS WBC phase shift is attributed to phase shifts of the winter monsoon and the NEC bifurcation, which are mostly related to those of the Indian Ocean Dipole Mode and Atlantic Multidecadal Oscillation, respectively. Understanding the SCS circulation low‐frequency variability is essential to forecast its thermodynamic state and regional climate effect.