Search

The Indonesian Throughflow (ITF) is significantly modulated by Indo-Pacific climate forcing, especially the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). However, when ENSO and IOD occur concurrently, they tend to play different roles in the ITF volume transport. By employing an improved Constructed Circulation Analogue (CCA) method, the relative contributions of these climate events to the ITF inflow and outflow transport in the upper and lower layers were quantified. The results indicate that during co-occurring El Niño and positive IOD events, ENSO is the dominant influence, with ratio values of 5.5:1 (3.5:1) in the upper layer and 1.7:1 (1.6:1) in the lower layer of the inflow (outflow). Conversely, during co-occurring La Niña and negative IOD events, the IOD predominates, with ratio values of 1:6 (1:6.5) in the upper layer and 1:4 (1:3) in the lower layer of the inflow (outflow). The mechanisms underlying these variations in the upper and lower layers can be explained by the differences in sea level anomaly (SLA) and wave propagation, respectively. This study provides a new insight into distinct roles of climate forcing on the ITF volume transport during the simultaneous occurrence of multiple climate modes. [ABSTRACT FROM AUTHOR]

Earlier proxy‐observational studies, and a sole modeling study, suggest that the Indian Ocean Dipole (IOD), an important global climate driver, exhibited multi‐scale temporal variability during the Last Millennium (LM; CE 0851–1849, with relatively high number of strong positive IOD events during the Little Ice Age (LIA; CE 1550–1749), and strong negative IOD events during the Medieval Warm Period (MWP; CE 1000–1199). Using nine model simulations from the PMIP3, we study the IOD variability during the LM after due validation of the simulated current day (CE 1850–2005) IOD variability. Majority of the models simulate relatively higher number of positive IOD events during the MWP, and negative IOD events in the LIA, commensurate with simulated background conditions. However, higher number of strong positive IOD events are simulated relative to the negative IODs during the LIA, in agreement with proxy‐observations, apparently owing to increased coupled feedback during positive IODs. Plain Language Summary: The Indian Ocean Dipole (IOD) is a natural climate phenomenon in the tropical Indian Ocean with significant global impacts. Positive IOD (pIOD) events are apparently occurring more frequently in recent decades, which may also be due to under‐sampling associated with limited observations span. Analyzing outputs for last millennium (CE 850–1850) from climate models, validated for historical period, helps in generating relatively longer‐period the paleo‐IOD records. Our analysis of simulations of the last thousand years from multiple models indicates relatively more positive (negative) IOD events in medieval warm period—CE 1000–1200 (Little Ice Age—CE 1550–1749). While during the ICA, background conditions similar to a negative IOD were simulated, models also simulate an increase in relatively‐stronger positive IOD events in its latter part, in agreement with a proxy‐climate record. The simulated centennial changes in positive and negative IOD frequencies are associated with changes in coupled ocean‐atmospheric feedback mechanisms. Key Points: Change in the Indian Ocean mean state from the medieval warm period (MWP) to the Little Ice Age (LIA)Despite negative IOD‐like background conditions in the LIA, models and paleo‐data show more stronger positive IODs thenThere are significant changes in feedback mechanisms of IODs from the MWP to LIA [ABSTRACT FROM AUTHOR]

Wind speed is an important parameter reflecting the climate and environmental conditions on the Earth's surface. It is also a pivotal factor influencing wind energy, a renewable and clean energy source. The mechanisms exerting influence on the surface wind speed over China, which have been mentioned in previous studies, include the temperature difference between the high and low latitudes of China, surface drag force, and climatic factors such as the Arctic Oscillation (AO), Pacific Decadal Oscillation (PDO), and El Niño-Southern Oscillation (ENSO). The Indian Ocean Dipole (IOD), which has attracted increasing attention during the past two decades, is an important climatic factor that exerts a significant influence on the climate and environment in the areas surrounding the Indian Ocean and globally. However, to date, it has not been reported whether the IOD is a climatic factor that significantly affects surface wind speed in China. Coastal South China is one of the most economically developed areas in China, and wind energy is becoming an important energy source in this area. An investigation of the relationship between the IOD and wind speed variations in coastal South China and their connecting mechanisms would contribute substantially to the understanding of the controlling mechanisms of climatic and environmental variations in coastal South China as well as to the planning of sustainable development in this area. Based on observations of surface wind speed in coastal South China, reanalysis data from the National Center of Environment Prediction (NCEP) and the National Center of Atmospheric Research (NCAR), research on the IOD over the last two decades, the effects of IOD activities on surface wind speed in coastal South China, and the controlling mechanisms were investigated using statistical analyses and atmospheric circulation variations. The results indicate that, regardless of the temporal or spatial scale, variations in the surface wind speed in coastal South China show significant positive correlations with the dipole mode index (DMI), which is a proxy for IOD activity. An increase in the DMI index (indicating a strengthening of IOD activity) corresponds to a decrease in the surface wind speed in coastal South China, and vice versa. This suggests that, in addition to the factors suggested in previous studies, which include the temperature difference between high and low latitudes, AO, PDO, and ENSO, IOD activity is also one of the most important factors affecting surface wind speed variation in coastal South China. The influence of IOD activity was weaker than that of the temperature difference between high and low latitudes. However, it played a more important role in the surface wind speed variation in this region than the AO, PDO, and ENSO. Strengthening of the IOD activity would enhance two anti-cyclones in the northwest Pacific and Bengal Bay, east of the Indian subcontinent, and, in turn, contribute to the reduction of surface wind speed variation in coastal South China. More serious global warming and increasing greenhouse gas emissions will further strengthen IOD activity in the future. Consequently, a greater decline in surface wind speed is expected in coastal South China, necessitating attention to sustainable wind energy use in this region. [ABSTRACT FROM AUTHOR]

The synergistic effects of the Indian Ocean Dipole (IOD) and El Nino Southern Oscillation (ENSO) have been investigated in this study over various subregions of India during 1981–2015. The IOD, is aperiodic and erratic, still this phenomenon is intrinsic in nature dependent on coupled ocean and atmospheric characteristics of the Indian ocean. About 60% of the IOD events showed its coexistence with ENSO during the 35-year recent climatology, still 40% of IOD events are independently occurring. For this analysis, the strongest three positive IOD (1994, 1997, 2006) and three negative IOD (1996, 1998, 2010) events have been identified that co-occurred with El-Nino and La-Nina events respectively. This study reveals that pIOD events are stronger and but the nIOD events are frequent and effecting Indian Summer Monsoon Rainfall (ISMR). The Sea Surface Temperature (SST) anomalies helps in explaining how strong pIOD favors moisture transport towards the western ghats, central India, northwest India, and anticyclonic conditions in the Bay of Bengal area whereas nIOD produces less rainfall in central India and the western ghats, but greater rainfall in the northeastern region. The reduced ENSO-IOD coupling in the 2000s may have strengthened the connection between ENSO and the Indian Summer Monsoon (ISMR), which had experienced a weakening in preceding decades, as reported by Kumar et al. (Science 284:2156–2159, 1999) and Ashok et al. (Geophys Res Lett 28:4499–4502, 2001). This study also investigates whether a regional climate model (RegCM4.7) accurately incorporate the realistic ENSO-IOD coupling mechanisms, and simulate its impact on regionalized precipitation during summer monsoon. The high-resolution RegCM4.7 simulations are close to the observation of rainfall during 2006, 1996 and 2010 extreme IOD events simulation that indicate RCM's higher sensitivity towards the abrupt change in boundary condition such as SST. Overall, the monsoon core regions i.e., central India, western ghats and northeast India, both IOD and southern oscillations are the synergistic predictor for the ISMR. [ABSTRACT FROM AUTHOR]

There is a vast upwelling area induced by the southeast monsoon in the waters off South Java, making the region an important fishing ground. Climate events can affect the variation of upwelling, but oceanographers have different understandings on the extent to which climate events control upwelling in this area, which leads to a lack of basis for studies on the evaluation and mechanisms of the variability of fishery resources in the region. The correlation between environmental parameters, including surface temperature (SST), chlorophyll-a (Chl-a) concentration, and climate event indices in South Java from 2003 to 2020 was analyzed. Results show that the Indian Ocean Dipole (IOD) has a greater influence on the interannual variability of upwelling intensity than ENSO. During the IOD, variations in equatorial latitudinal winds excite different types of Kelvin waves that anomalously deepen or shallow the thermocline, which is the main cause of anomalous variations in upwelling, independent of variations in the local wind field. A correlation between the interannual variability in upwelling and the annual catches was revealed, showing that climatic events indirectly affect fishery resources through upwelling effects. During positive IOD/El Niño periods, strong upwelling delivers more nutrients to the surface layer, which favors fish growth and reproduction, resulting in higher annual catches. A negative IOD/La Niña, on the other hand, leads to weaker upwelling and fewer nutrients into the surface waters. Fish tend to move in deeper waters, making traditional fishing methods less efficient and consequently lower annual catches. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) summer monsoon (SCSSM) and Western North Pacific tropical cyclones (TCs) are both tropical systems that interact with each other on multiple scales. This study examines the differences in TCs activity characteristics between anomalous strong and weak SCSSM years, and explores the possible mechanisms behind these differences through the coupling relationship between tropical atmospheric circulation and oceanic surface conditions. Results show that the destructiveness of TCs over the Western North Pacific is stronger during weak SCSSM years than in strong years, whereas the opposite occurs for TCs over the SCS. The interaction between the tropical Indo-Pacific ocean and atmosphere plays a key role in the relationship between SCSSM intensity and TCs activity. In strong (weak) SCSSM years, the sea surface temperature anomaly (SSTA) in the tropical Pacific Ocean tends to correspond to a La Niña-like (El Niño-like) distribution, whereas the tropical Indian Ocean shows an Indian Ocean dipole-negative (positive) phase distribution. Moreover, Walker circulations in both the Indian and Pacific Oceans are coupled during these years, which creates a seesaw-like relationship in the conditions for TCs formation between the SCS and the Western Pacific Ocean. During weak SCSSM years, the formation and activity of TCs over the SCS are suppressed due to the weakened water vapor transport caused by abnormal easterly winds from the eastern Indian Ocean to the southern SCS. Meanwhile, the higher SSTA in the Western Pacific Ocean enhances the TCs activity. In strong SCSSM years, the enhanced monsoon drives a stronger monsoon trough, improving the convective environment over the SCS, whereas in contrast, the Western Pacific Ocean is covered by colder water, resulting in poorer conditions for TCs genesis. [ABSTRACT FROM AUTHOR]

The Southern Indonesian (SI) region is known for its high-intensity coastal upwelling caused by monsoonal wind. Interannual phenomena such as El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) also influence upwelling activity in this region. This study analyzed the relationship between upwelling intensity (UI sst) and those variables and their impact on oceanographic features such as Sea Surface Temperature (SST) and chlorophyll-a concentration. We used satellite imagery data, including SST from the National Oceanic and Atmospheric Administration (NOAA) and chlorophyll-a from MODIS, to analyze the aforementioned issue. To identify the impact of wind patterns on coastal upwelling, we analyzed using zonal wind stress from ERA-5 Data. Quantification of UI sst is defined as the SST gradient between the coastal and open ocean waters. Linear and partial correlation analysis between UI sst with the Ocean Niño Index (ONI) and Dipole Mode Index (DMI) were conducted to see the influence of ENSO and IOD phenomena. Anomaly analysis was also conducted on SST, chlorophyll-a concentration, zonal windstress and UI sst to see how large the values were during the years of the ENSO and IOD events. Upwelling in the SI region typically occurs during southeast monsoon (SEM) periods, starting earlier in the East side (Nusa Tenggara Islands) and moving towards the West side (South Coast of Java). The correlation analysis (both linear and partial) indicates that the IOD has a stronger influence on UI sst in the SI region compared to ENSO, especially during June to October (SEM periods). This finding is confirmed by anomaly analysis, which reveals significant changes in SST, chlorophyll-a concentration, zonal windstress, and UI sst during ENSO and IOD events. The magnitude of the anomalies is generally stronger during IOD events than those observed under ENSO conditions. • Remote sensing satellite data can identify the variability of upwelling phenomena in the Southern Indonesian (SI) seas. • The strength of upwelling intensity in SI is strongly influenced by Interannual phenomena such as the ENSO and IOD. • Sea Surface Temperature and Chlorophyll-a anomalies confirm the influence of changes in upwelling intensity by ENSO and IOD. • IOD has a stronger influence than ENSO on Upwelling intensity in the SI Region. [ABSTRACT FROM AUTHOR]

Wildfires are sensitive to climate change, but their response to changes in temperature and precipitation on long timescales is still disputed. In this study, we present a ~9.4 ka black carbon mass sedimentation rate (BCMSR) record from Lake Ximenglongtan (XMLT), southwestern China, to elucidate the Holocene fire regime and its linkages to climatic conditions. The results indicate that the regional fire activity was low during the early Holocene (before 7.6 cal ka BP), increased notably at 7.6 cal ka BP, and continued to increase gradually during the mid- to late Holocene until 2.2 ka. The episodes of higher fire occurrence reflected by higher BCMSR over the last 2.2 ka might be more likely related to the intensified human activities. The cool and humid climate during the early Holocene limited the spread of fire, while warming and drying at ~7.6 cal ka BP triggered higher fire occurrence. Instead of temperature, changes in precipitation dominated fire regime variation during the mid- to late Holocene. On millennial timescales, we suggest that Holocene fire variability has been predominantly controlled by the combined effects of Northern Hemisphere (NH) summer and winter insolation that influenced monsoonal precipitation and fire season temperature, respectively. Indian Ocean Dipole (IOD) events may also have affected fire incidence through influencing monsoon intensity. [ABSTRACT FROM AUTHOR]

Indian Ocean decadal sea-level variability is an active research area, with many unresolved questions due to inadequate observational coverage. In this study, we analyse 26 Coupled Model Intercomparison Project (CMIP) pre-industrial simulations and isolate two consistent modes of Indian Ocean variability, which collectively explain about 50% of the total decadal sea-level variance. With opposite sea-level signals in the southwestern and eastern Indian Ocean, the first mode is related to decadal modulation of the Indian Ocean Dipole (DIOD) and equatorial wind-driven dynamics. Though IOD is more independent of the El Niño–Southern Oscillation (ENSO) at decadal (r ~ 0.4) than interannual (r ~ 0.6) timescales, the DIOD–ENSO co-variability yields sea-level signals along the west coast of Australia, transmitted from the western Pacific via the Indonesian Throughflow. The second mode encompasses variability in the south Indian Ocean (SIODV), exhibiting a broad monopolar sea-level pattern east of Madagascar. In about half of the models, the SIODV is largely independent from DIOD (and decadal ENSO) and driven by south Indian Ocean wind-stress curl associated with meridional shifts in the Mascarene High (MH). In the other models, the SIODV lags the DIOD about 3 years. In those models, in addition to MH forcing, the DIOD-related alongshore wind stress off the northwest Australian coast triggers Rossby waves that also contribute to the SIODV, further west. The DIOD and MH forcing are mutually independent (r ~ 0.2). The results are broadly consistent with sea-level variations derived from the short altimeter data, despite an underestimation of the Oceanic bridge signals in CMIP models. [ABSTRACT FROM AUTHOR]

Modes of climate variability are known to influence rainy season onset, but there is less understanding of how they impact flood timing. We use streamflow reanalysis and gauged observation data sets to examine the influence of the Indian Ocean Dipole and El Niño–Southern Oscillation across sub‐Saharan Africa. We find significant changes in flood timing between positive and negative phases of both Indian Ocean Dipole and El Niño–Southern Oscillation; in some cases the difference in the timing of annual flood events is more than three months. Sensitivity to one or other mode of variability differs regionally. Changes in flood timing are larger than variability in rainy season onset reported in the literature, highlighting the need to understand how the hydrological system alters climate variability signals seen in rainy season onset, length, and rainfall totals. Our insights into flood timing could support communities who rely on flood‐based farming systems to adapt to climate variability. Plain Language Summary: Patterns of climate variability such as the El Niño–Southern Oscillation or the Indian Ocean Dipole affect the timing of the start of the rainy season, but little is known about how this translates into changes in the timing of the annual flood in rivers. We use computer model reconstructions and observed records of river flows in Africa to understand how these patterns of climate variability are changing the timing of river floods. In eastern and southern Africa, in particular, the differences in flood timing can be more than three months. This information could help farmers in African floodplains to adapt their water management, planting, and cropping practices to these patterns of climate variability. Key Points: Modes of climate variability in the Pacific and Indian Oceans drive significant changes in flood timing across sub‐Saharan AfricaThe hydrological system enhances and alters climate variability signals seen in rainy season onset, duration, and total rainfallUnderstanding of how climate variability changes the timing of floods can support flood‐based farming systems [ABSTRACT FROM AUTHOR]

Abstract: The impacts of explosive volcanism on the densely populated Indian Ocean (IO) region remain elusive. Dedicated sensitivity experiments indicate that tropical volcanic eruptions induce a stronger surface cooling over Africa than of ocean, promoting westerlies in the equatorial IO. These westerlies drive a subsurface response reminiscent to that of a negative IO Dipole (IOD) during autumn in the year of eruption. The eruption also drives an enhanced cooling over the northwestern IO as a direct response to climatological cloud cover distribution. The resulting anomalous zonal sea surface temperature gradient contributes to enhance equatorial westerly anomalies in summer. The response is sensitive to the IO preconditioning, being larger when the system is favorable to a positive IOD development. Volcanic eruptions also induce a subsurface IOD‐like response in the multimodel database from the Coupled Model Intercomparison Project Phase 5 as well as a primary productivity decrease in the eastern IO. [ABSTRACT FROM AUTHOR]

The dynamics of the teleconnection between the Indian Ocean Dipole (IOD) in the tropical Indian Ocean and El Niño-Southern Oscillation (ENSO) in the tropical Pacific Ocean at the time lag of one year are investigated using lag correlations between the oceanic anomalies in the southeastern tropical Indian Ocean in fall and those in the tropical Indo-Pacific Ocean in the following winter-fall seasons in the observations and in high-resolution global ocean model simulations. The lag correlations suggest that the IOD-forced interannual transport anomalies of the Indonesian Throughflow generate thermocline anomalies in the western equatorial Pacific Ocean, which propagate to the east to induce ocean-atmosphere coupled evolution leading to ENSO. In comparison, lag correlations between the surface zonal wind anomalies over the western equatorial Pacific in fall and the Indo-Pacific oceanic anomalies at time lags longer than a season are all insignificant, suggesting the short memory of the atmospheric bridge. A linear continuously stratified model is used to investigate the dynamics of the oceanic connection between the tropical Indian and Pacific Oceans. The experiments suggest that interannual equatorial Kelvin waves from the Indian Ocean propagate into the equatorial Pacific Ocean through the Makassar Strait and the eastern Indonesian seas with a penetration rate of about 10%-15% depending on the baroclinic modes. The IOD-ENSO teleconnection is found to get stronger in the past century or so. Diagnoses of the CMIP5 model simulations suggest that the increased teleconnection is associated with decreased Indonesian Throughflow transports in the recent century, which is found sensitive to the global warming forcing. [ABSTRACT FROM AUTHOR]

Water availability and food security are tightly coupled on a global scale. The occurrence of drought puts this balance at risk due to reductions in dryland farming production and water allocations to irrigated agriculture. Improved understanding of drought initiation and cessation would therefore be beneficial for drought planning and management. The study objective was to determine factors affecting drought initiation and cessation over the past century in two climatologically similar regions that represent net agricultural exporters; south central U.S. (Texas) and southeast Australia (Murray Darling Basin, MDB). Drought indices included the Standardized Precipitation Index (SPI, 1900–2014) for meteorological drought, the Normalized Difference Vegetation Index (NDVI, 1981–2014) for agricultural drought, and the Streamflow Drought Index (SDI, 1930–2014) for hydrological drought. Results show that meteorological drought tends to develop gradually over a period of up to six months, with agricultural drought developing shortly thereafter (within one month) in both regions. Evidence of hydrological drought was observed within one month (Texas) and within four months (MDB) on average after meteorological drought was established. Further, droughts appear to cease more quickly than they initiate over Texas, whereas rates of drought initiation and cessation are similar over the MDB. Drought breaking rainfall in Texas is generally a result of a southward shift in the Polar Jet Stream or a low-pressure trough over central North America, whereas drought cessation in the MDB is typically associated with a monsoon trough or low-pressure system in the Tasman Sea/Great Australian Bight. Improved knowledge of the climate mechanisms controlling the onset and termination of drought periods should enhance drought forecasts and improve drought management practices, particularly in regions where water security is a primary objective. [ABSTRACT FROM AUTHOR]

The different impacts of El Niño during peak phases with and without a positive Indian Ocean Dipole (P-IOD) on the Northwest Pacific circulation were studied. The authors focused on the Northwest Pacific circulation features in the mature phase of El Niño from September to February of the next year. Composite maps and simulations demonstrate that the atmospheric circulation under the impact of El Niño with and without P-IOD exhibits large differences in temporal evolution and intensity. In single El Niño (SE) years without a P-IOD, an anomalous low-level anticyclonic circulation around the Philippines (PSAC) is instigated by the single El Niño-induced Indonesian subsidence. However, during the years when El Niño and a P-IOD matured simultaneously, a much greater anomalous subsidence over the western Pacific and the Maritime Continent occurred. The PSAC tends to occur earlier, is much stronger and has a longer lifetime than that during SE. More importantly, the PSAC shows a characteristic of an eastward movement from the southern South China Sea (SCS) to the Philippine Sea. This characteristic does not appear during SE. These patterns imply that a positive IOD event tends to exert a prominent influence on the PSAC during El Niño events and there is a combined impact of El Niño and P-IOD on the development of the PSAC. [ABSTRACT FROM AUTHOR]

Lag correlations between sea surface temperature anomalies (SSTA) in the southeastern tropical Indian Ocean (STIO) in fall and Niño 3.4 SSTA in the eastern equatorial Pacific in the following fall are subjected to decadal variation, with positive correlations during some decades and negative correlations during others. Negative correlations are smaller and of shorter duration than positive correlations. Variations in lag correlations suggest that the use of the Indian Ocean Dipole (IOD) as a predictor of the El Niño-Southern Oscillation (ENSO) at a lead time of one year is not effective during some decades. In this study, lag correlations between IOD and ENSO anomalies were analyzed to investigate why the IOD-ENSO teleconnection disappears during decades with negative correlations. Anomalies induced by the IOD in the equatorial Pacific Ocean during decades with negative correlations are still present, but at a greater depth than in decades with positive correlations, resulting in a lack of response to oceanic channel dynamics in the cold tongue SSTA. Lag correlations between oceanic anomalies in the west Pacific warm pool in fall and the equatorial Pacific cold tongue with a one-year time lag are significantly positive during decades with negative correlations. These results suggest that oceanic channel dynamics are overwhelmed by ocean-atmosphere coupling over the equatorial Pacific Ocean during decades with negative correlations. Therefore, the Indonesian throughflow is not effective as a link between IOD signals and the equatorial Pacific ENSO. [ABSTRACT FROM AUTHOR]

The Indian Ocean sea surface temperature (SST) variability has been represented with the two dominant variability modes: the Indian Ocean basin-wide (IOBW) and dipole (IOD) modes. Here we investigate future changes of the two modes together with mean state and El Niño and Southern Oscillation (ENSO) relationship under the anthropogenic global warming using 20 coupled models that participated in the phase five of Coupled Model Intercomparison Project by comparing the historical run from 1950 to 2005 and the RCP 4.5 run from 2050 to 2099. The five best models are selected based on the evaluation of the 20 models' performances in simulating the two modes and Indian Ocean basic state for the latest 56 years. They are capable of capturing the IOBW and IOD modes in their spatial distribution, seasonal cycle, major periodicity, and relationship with ENSO to some extent. The five best models project the significant changes in the Indian Ocean mean state and variability including the two dominant modes in the latter part of twenty-first century under the anthropogenic warming scenario. First, the annual mean climatological SST displays an IOD-like pattern change over the Indian Ocean with enhanced warming in the northwestern Indian Ocean and relatively weaker warming off the Sumatra-Java coast. It is also noted that the monthly SST variance is increased over the eastern and southwestern Indian Ocean. Second, the IOBW variability on a quasi-biennial time scale will be enhanced due to the strengthening of the ENSO-IOBW mode relationship although the total variance of the IOBW mode will be significantly reduced particularly during late summer and fall. The enhanced air-sea coupling over the Indian-western Pacific climate in response to El Nino activity in the future projection makes favorable condition for a positive IOD while it tends to derive relatively cold temperature over the eastern Indian Ocean. This positive IOD-like ENSO response weakens the relationship between the eastern Indian Ocean and El Nino while strengthens the relationship with western Indian Ocean. Third, the IOD mode, intrinsic coupled mode of the Indian Ocean may not be changed appreciably under the anthropogenic global warming. [ABSTRACT FROM AUTHOR]

The relationship between the number of lightning flashes (NLF) and the cosmic ray flux (CRF) during the period of ENSO (El Niño/La Niña Southern Oscillations) with and without IOD (Indian Ocean Dipole) has been studied for the first time in the region of South/Southeast Asia (8°N–35°N and 60°E–120°E) to the authors' knowledge. Our analysis shows that the relationship is governed by regional meteorology and not by direct solar influence. Unlike on global scale, the data during ENSO are important for this relationship on regional scale. CRF and NLF are in statistically significant relationship only when CRF is significantly correlated with the meteorological parameters. CRF and NLF are significantly correlated during the period of ENSO with IOD (ENSO–IOD) but not during the period of ENSO without IOD (ENSO). The Aerosol Optical Depth (AOD), the positive temperature anomaly (TA) and an increase in TA may be responsible for this relationship during the ENSO–IOD period. On the shorter temporal/spatial scale, meso-scale meteorological parameters are responsible for the negative correlation between the CRF and the NLF. On the other hand, on the longer scale, an amount of Low Level Cloud Fraction (LLCF) is responsible for the positive correlation between the CRF and the NLF. Our partial correlation analysis shows that controlling for the AOD weakens the correlation between the CRF and the NLF but does not affect that between the 12month running means of the same. Thus, aerosols are responsible during the total study period and during the IOD period for enhancing the significant CRF–NLF relationship. Solar radio flux F10.7 cm (SRF10.7) seems to be the main controlling parameter for the stronger relationship. We find that there is a distinct difference in the average magnitude of different solar and meteorological parameters between that during the ENSO period and the ENSO–IOD period which may be attributed to the difference in cloud types and aerosol properties between the two periods. The results of our analysis may be confirmed with longer data sets and more number of IOD events in the future. [ABSTRACT FROM AUTHOR]

Highlights: [•] We modelled rainfall using multiple regression and Artificial Neural Networks for Victoria, Australia. [•] We examined combined lagged months of ENSO and IOD as potential predictors of spring rainfall. [•] Spring rainfall was predicted three years in advance with the developed models using ENSO–IOD lagged months. [•] ANN models proved to be more accurate than multiple regression models in terms of long term predictions. [ABSTRACT FROM AUTHOR]

This study examines the temporal patterns of precipitation and the influence of large-scale climate anomalies in the Pearl River basin (South China), with particular focus on sub-basin scale. Three popular data analysis techniques are employed: (1) wavelet analysis; (2) principal component analysis (PCA); and (3) rank correlation method. With due consideration to hydrologic factors, water resources activities, and large-scale climate data, the entire basin is divided into ten sub-basins and the analysis is performed on monthly data. The wavelet analysis reveals discernible differences in temporal scales of fluctuation embedded in the monthly precipitation anomalies over the basin. The PCA delineates three coherent regions exhibiting similar distribution of variability across scales. Analysis of linkages between precipitation and teleconnection patterns using cross-wavelet transform and wavelet coherence reveals that the dominant variabilities of precipitation are essentially depicted by the Indian Ocean Dipole (IOD), especially for the central and eastern part of the Pearl River basin. On the influence of El Niño-Southern Oscillation (ENSO) signal on precipitation, more significant correlation is detected for the eastern part of the basin, long-term relationships (within 4-8 years band) are found for the western part of the basin, while the central part seems to be acting as a transition zone. Rank correlations of scale-averaged wavelet power between regional precipitation and climate indices for the dominant low-frequency variability band (0.84-8.40 years) provide further support to the different precipitation-climate relationships for different regions over the basin. The present results provide valuable information towards: (1) improving predictions of extreme hydroclimatic events in the Pearl River basin, based on their relationships with IOD or ENSO; and (2) devising better adaptation and mitigation strategies under a future changing climate. [ABSTRACT FROM AUTHOR]

The Madden–Julian oscillation (MJO) is the main component of intraseasonal variability of the tropical convection, with clear climatic impacts at an almost-global scale. Based on satellite observations, it is shown that there are two types of austral-summer MJO events (broadly defined as 30–120 days convective variability with eastward propagation of about 5 m/s). Equatorial MJO events have a period of 30–50 days and tend to be symmetric about the equator, whereas MJO events centered near 8°S tend to have a longer period of 55–100 days. The lower-frequency variability is associated with a strong upper-ocean response, having a clear signature in both sea surface temperature and its diurnal cycle. These two MJO types have different interannual variations, and are modulated by the Indian Ocean Dipole (IOD). Following a negative IOD event, the lower-frequency southern MJO variability increases, while the higher-frequency equatorial MJO strongly diminishes. We propose two possible explanations for this change in properties of the MJO. One possibility is that changes in the background atmospheric circulation after an IOD favour the development of the low-frequency MJO. The other possibility is that the shallower thermocline ridge and mixed layer depth, by enhancing SST intraseasonal variability and thus ocean–atmosphere coupling in the southwest Indian Ocean (the breeding ground of southern MJO onset), favour the lower-frequency southern MJO variability. [ABSTRACT FROM AUTHOR]

Abstract: Trace element and stable isotope ratios from an active stalagmite (LR06-B1) recovered from Liang Luar Cave on the island of Flores (eastern Indonesia) are used to reconstruct the position of the austral summer inter-tropical convergence zone and Australian-Indonesian summer monsoon variability during the Holocene. Uranium-series dating of the stalagmite shows that it commenced growth 12,640years ago, with hiatuses spanning 8,560 to 6,420 and 3,670 to 2,780years ago. Stalagmite Mg/Ca and Sr/Ca ratios correlate significantly with one another, and with δ 18O and δ 13C, throughout the record. This suggests that the Mg/Ca and Sr/Ca ratios are dominated by prior calcite precipitation, a process whereby degassing in the vadose zone during periods of low recharge causes deposition of calcite and disproportionate loss of Ca2+ ions (relative to Mg2+ and Sr2+) ‘upstream’ of the stalagmite. The degree of initial 234U/238U disequilibrium also appears to have been controlled by recharge to the overlying aquifer. Together with the Mg/Ca, Sr/Ca, and δ 18O values, the initial uranium isotope activity ratios ([234U/238U]I) imply a generally drier early Holocene, coincident with a lower sea level and lower Southern Hemisphere summer insolation. Comparison of speleothem δ 18O time-series from Flores and Borneo shows that they vary in unison for much of the Holocene. However, there is a significant decrease in the Borneo δ18O record ~6,000 to 4,000 years ago that does not occur in the Flores record. This anomaly may be related to a change in the Australian-Indonesian summer monsoon circulation in response to a protracted positive phase of the Indian Ocean Dipole. Under this scenario, stronger upwelling off of western Indonesia would, based on present-day effects, result in reduced summer convective activity over Flores and a subsequent northward shift of the intertropical convergence zone. [Copyright &y& Elsevier]

Indian Ocean Dipole (IOD) is a large-scale physical ocean phenomenon in the Indian Ocean that plays an important role in predicting the El Nino Southern Oscillation in the tropical Pacific. Predicting the occurrence of IOD is of great significance to the study of climate change and other marine phenomena. Generally, the IOD index is calculated to judge whether the IOD occurs. In this paper, a convolutional LSTM (convLSTM) neural network is used to build the deep learning model to predict the sea surface temperature in the next seven months and calculate the IOD index. Through the analysis of marine atmospheric data with complex temporal and spatial relationships, the wind field signal knowledge of the physical ocean is introduced to predict IOD phenomenon by combining the prior knowledge of the physical ocean and deep learning. The experimental results show that the average correlation of IOD index time series to the true IOD index time series is 82.87% from 2015 to 2018, seven months ahead for IOD prediction. IOD manifests as sea surface temperature (SST) anomaly changes, and this thesis verifies that the wind field signal information has a positive impact on the prediction of IOD changes. Moreover, the convLSTM can predict this anomaly better. The IOD index line graph can generally fit the real IOD index variation trend, which has a profound impact on the study of the IOD phenomenon. [ABSTRACT FROM AUTHOR]

The Indian Ocean Dipole (IOD) has major climate impacts worldwide, and most profoundly for nations around the Indian Ocean basin. It has been 20 years since the IOD was first formally defined and research since that time has focused primarily on examining IOD dynamics, trends and impacts in observational records and in model simulations. However, considerable uncertainty exists due to the brevity of reliable instrumental data for the Indian Ocean basin and also due to known biases in model representations of tropical Indian Ocean climate. Consequently, the recent Intergovernmental Panel on Climate Change (IPCC) report on the Ocean and Cryosphere in a Changing Climate (SROCC) concluded that there was only low confidence in projections of a future increase in the strength and frequency of positive IOD events. This review examines the additional perspectives that palaeoclimate evidence provides on IOD trends, variability, interactions with the El Niño–Southern Oscillation (ENSO), and impacts. Palaeoclimate data show that recent trends towards more frequent and intense positive IOD events have been accompanied by a mean shift toward a more positive IOD-like mean zonal SST gradient across the equatorial Indian Ocean (due to enhanced warming in the west relative to the east). The increasing frequency of positive IOD events will imminently move outside of the range of natural variability in the last millennium if projected trends continue. Across a range of past climate states, periods of a mean positive IOD-like state in the Indian Ocean have been accompanied by elevated IOD variability. This includes events that exceed the magnitude of even the strongest measured historical events, demonstrating that the Indian Ocean can harbour even stronger variability than what has been observed to date. During the last millennium there has been a tight coupling between the magnitude of interannual IOD and ENSO variability, although positive IOD events have frequently occurred without any indication of a co-occurring El Niño event. This IOD–ENSO coupling may not have persisted across past climates that were very different from the present, raising questions of whether their interaction will change in a rapidly warming future. Palaeoclimate evidence for hydroclimate changes during the last millennium further points to the importance of interannual IOD and ENSO variability in providing the rainfall that breaks droughts in regions that are impacted by these modes of variability. Overall, this review highlights the rich insights into the IOD that can be gained from palaeoclimate evidence. Palaeoclimate data helps to overcome known limitations in observations and model simulations of the IOD, and demonstrates that strong conclusions about the IOD and its impacts can be reached when the evidence for past, present and future behaviour of the IOD are assessed together. • Rich insights into the Indian Ocean Dipole can be gained from palaeoclimate evidence. • Rising frequency of positive IOD events will imminently move outside natural range. • Indian Ocean can harbour even stronger variability than observed in recent decades. • Indo-Pacific covariance is strong today, but not always in the past. • Strong Indo-Pacific variability was important in breaking droughts in last 1000 years. [ABSTRACT FROM AUTHOR]

This study analyzed the sensitivity of rainfall patterns in South China and the Indochina Peninsula (ICP) using statistical simulations of observational data. Quantitative changes in rainfall patterns over the ICP were examined for both wet and dry seasons to identify hotspots sensitive to ocean warming in the Indo-Pacific sector. The rainfall variability was amplified by combined and/or independent effects of the El Niño–Southern Oscillation and the Indian Ocean Dipole (IOD). During the years of El Niño and a positive phase of the IOD, rainfall is less than usual in Thailand, Cambodia, southern Laos, and Vietnam. Conversely, during the years of La Niña and a negative phase of the IOD, rainfall throughout the ICP is above normal, except in parts of central Laos, northern Vietnam, and South China. This study also simulated the change of ICP rainfall in the wet and dry seasons with intentional IOD changes and verified IOD-sensitive hotspots through quantitative analysis. The results of this study provide a clear understanding both of the sensitivity of regional precipitation to the IOD and of the potential future impact of statistical changes regarding the IOD in terms of understanding regional impacts associated with precipitation in changing climates. [ABSTRACT FROM AUTHOR]

El Niño/Southern Oscillation (ENSO) teleconnections present a hemispheric dipole pattern in both rainfall and vegetation between eastern and southern Africa. We analyze precipitation and normalized difference vegetation index (NDVI) departures during the 2015–2017 ENSO cycle; with one of the strongest warm events (El Niño) on record followed by a short and weak cold event (La Niña). Typically, southern (eastern) Africa is associated with dry (wet) conditions during El Niño, and wet (dry) conditions during La Niña. In general, the temporal and spatial evolution of vegetation responses show the expected dipole pattern during the 2015–2016 El Niño and following 2016–2017 La Niña. However, in 2015–2016 the eastern African impacts were displaced to the west and south of the canonical pattern. Composites of seasonal vegetation anomalies highlight the magnitude and position of impacts. Further investigation through empirical orthogonal teleconnections and spatial correlation analysis confirms the similar, but opposite, teleconnection impacts in eastern and southern Africa. The diametrically opposed patterns have particular implications for agricultural production and the availability of fodder and forage, especially in the pastoral communities of the two regions. [ABSTRACT FROM AUTHOR]