Strong El Nino Southern Oscillation Research Articles

The history of the El Niño–Southern Oscillation and sea surface salinity during 1376–1500 CE reconstructed by Porites coral δ18O from Huangyan Island, South China Sea

The El Niño–Southern Oscillation (ENSO) is the most influential climatic phenomenon affecting global ecosystems, water use, and agriculture on an interannual scale. However, limited instrumental records make it difficult to fully understand the characteristics of ENSO events. In this study, we used both monthly-resolved Porites coral δ18O records, i.e., living Porites corals of δ18O–HYDL4 (1992–2015) and subfossil Porites corals of δ18O–HYD3 (1376–1500 CE), from Huangyan Island in the South China Sea (SCS), to reconstruct the moderate intensity ENSO and sea surface salinity (SSS) during 1376–1500 CE. The results show that the SSS was higher but the frequency of moderate-to-high intensity ENSO events was lower than the present during 1376–1500 CE. ENSO activity was generally similar to or slightly lower than that of today, but it included several very strong ENSO events in the first substage (1376–1450 CE), while it was relatively quiet in the second substage (1451–1500 CE). More moderate-intensity ENSO events may have occurred in the relatively warm climate. The variation in coral δ18O was dominated by multiple factors in this region. SST, ENSO and the Pacific Decadal Oscillation (PDO) may be the dominant factors influencing the changes in coral δ18O at different timescales.

Paired coral Sr/Ca and δ18O records reveal increasing ENSO influence on Malaysian Borneo's hydroclimate

The El Niño Southern Oscillation (ENSO) is a worldwide climate phenomenon impacting temperatures and precipitation regimes across the globe. Previous studies have shown this climate phenomenon to influence Malaysian Borneo's hydroclimate. In the context of a changing climate and increasingly strong extreme ENSO events, understanding the influence of ENSO on this region, and its evolution through time, is essential to better constrain the future impacts it will have on the Maritime Continent's hydroclimate. Here, we used coupled δ18O and Sr/Ca records from massive corals' carbonate calcium skeletons to build a proxy for past hydroclimate: δ18Oseawater (δ18Osw) and compensate for the limited dependable instrumental data in most of the 20th century. We assessed our two 90 and 60-year-long δ18Osw records' quality as proxies for regional hydroclimate by correlating them with different instrumental salinity datasets before performing moving windowed correlations with the NINO3.4 index, an indicator of ENSO state.Results show that agreement between geochemical proxies and instrumental data highly depends on the chosen dataset, study site location, period, and monsoon season, with stronger agreement with more recent data, pointing towards insufficient data quality when going far back in time. More importantly, when correlated against the NINO3.4 index, our δ18Osw records showed a growing correlation for most of their respective lengths. From the 1980s, we found an increasing influence of ENSO on the local hydroclimate with correlation coefficients r > 0.8 during the wet monsoon season. Our findings highlight the differences in results depending on the chosen observational dataset, time scale, or period of the year, and stress the importance of such geochemical archives to better understand the impacts of ENSO across periods predating reliable instrumental data. More importantly, our findings show how the concurrent evolution of the IOD, and the PDV affect ENSO and ultimately, northwestern Borneo's hydroclimate through their teleconnections.

The impact of global warming on ENSO from the perspective of objective signals

Most studies on the relationship between global warming and El Niño-Southern Oscillation (ENSO) rely on simulation experiments, but they have produced contradictory results, which cannot guarantee the reliability of the experimental findings. To address this challenge, we approached the issue from the perspective of objective ENSO and global warming signals. The effects of global warming on ENSO are not limited to the Earth's surface, but also present in the atmosphere. While objective monitoring indices exist for surface global warming and ENSO signals, objective ENSO and global warming signals in the atmosphere are difficult to obtain. To obtain high-precision ENSO and global warming signals in the atmosphere, we propose using the strategy of ICA (Independent Component Analysis) combined with a non-parametric method. The results of the objective ENSO and global warming signals suggest that the global warming signal leads the ENSO signal by approximately three months and exhibits a clear positive correlation with the ENSO signal, especially the occurrence of strong ENSO events is closely related to global warming, indicating that global warming promotes the occurrence of ENSO events. Under the influence of global warming, the frequency and intensity of ENSO increase, the characteristics and complexity of ENSO atmospheric teleconnections may be altered, and there is a greater tendency for more destructive El Niño events to occur. Since the beginning of the 21st century, the probability of ENSO event has increased significantly. Furthermore, moderate or strong ENSO events tend to develop earlier, and extreme ENSO events not only develop earlier but also prolong their decay phase, leading to an extended lifespan of ENSO events. This paper investigates the effect of global warming on ENSO from the perspectives of objective ENSO and global warming signals, which well supplements the objective factual basis for the previous simulation experimental studies.

Pacific‐Driven Salinity Variability in the Timor Passage Since 1777

AbstractSalinity in the Indonesian seas integrates regional oceanographic and atmospheric processes, such as Indonesian Throughflow (ITF) and monsoon rainfall. Here we present a multicentury (1777–1983) δ18O coral record from Nightcliff Reef, located in the Timor Passage off the coast of northern Australia, which we use to infer local salinity change. We show that Australian monsoon rainfall and ITF influence salinity at the study site. These reconstructed salinity changes in the Timor Passage correlate with changes in Pacific sea surface temperature (SST) modes, including the El Niño Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). While environmental stress creates challenging conditions for coral growth, this record particularly tracks the central Pacific signature of ENSO‐driven interannual variability, in agreement with reconstructions of rainfall across northern Australia. The strength of interannual variance in the record follows fluctuations in other local ENSO‐sensitive rainfall reconstructions, demonstrating a strong regional ENSO signature. However, this regional pattern differs from variance in composite ENSO reconstructions, suggesting that the multi‐site nature of these reconstructions may create biases. Salinity variability on decadal and longer time scales occurs throughout the record. Some of these oscillations are consistent with other ITF‐sensitive coral records. Our new salinity record adds a strongly Pacific‐sensitive record to the existing suite of regional paleoclimate reconstructions. Relationships among these records highlight the complexity of salinity in the Indonesian seas and the controls on its variability.

Wavelet Analysis of Ozone Driving Factors Based on ~20 Years of Ozonesonde Measurements in Beijing

A long-term vertical ozone observational dataset has been provided during 2001–2019 by ozonesonde measurements in Beijing on the North China Plain. Previous studies using this dataset primarily focused on the vertical characteristics of climatological ozone and its variation; however, the driving factors of ozone variation have not been well discussed. In this study, by applying the wavelet analysis method (including continuous wavelet transform and cross wavelet) and sliding correlation coefficients to ~20 years of ozonesonde measurements collected in Beijing, we analyzed the dominant modes of ozone column variability within three height ranges over Beijing (total column ozone: TOT; stratospheric column ozone: SCO; and tropospheric column ozone: TCO). Moreover, we also preliminarily discussed the relationship between these three ozone columns and the El Niño Southern Oscillation (ENSO), Quasi-biennial Oscillation (QBO), and 11-year solar activity cycle. The results revealed that the ozone columns within the three height ranges predominantly adhered to interannual variability patterns, and the short-term variabilities in TOT and SCO may have been related to eruptive volcanic activity. In comparison to the TOT and SCO, the TCO was more susceptible to the forcing influences of high-frequency factors such as pollutant transport. Similar to the results in other mid-latitude regions, strong ENSO and QBO signals were revealed in the interannual ozone column variability over Beijing. The TOT and SCO showed positive anomalous responses to ENSO warm-phase events, and the peak of the ENSO warm phase led the winter peaks of the TOT and SCO by approximately 3–6 months. During the strong cold–warm transition phase in 2009–2012, the TOT and SCO showed a significant positive correlation with the ENSO index. The strong seasonality of the meridional circulation process driven by the QBO led to a significant positive correlation between the QBO index and the TOT and SCO in the interannual cycle, except for two periods of abnormal QBO fluctuations in 2010–2012 and 2015–2017, whereas the TCO showed a time-lagged correlation of approximately 3 months in the annual cycle relative to the QBO due to the influence of the thermodynamic tropopause. In addition, analysis of the F10.7 index and the ozone columns revealed that the ozone columns over Beijing exhibited lagged responses to the peaks of sunspot activity, and there was no obvious correlation between ozone columns and 11-year solar activity cycle. Given the complex driving mechanism of the climatic factors on local ozone variability, the preliminary results obtained in this study still require further validation using longer time series of observational data and the combination of chemical models and more auxiliary data.

Diverse Impacts of ENSO on the Intensity of Tropical Western North Pacific Synoptic‐Scale Disturbances During Boreal Summer

AbstractPresent study analyzes diverse impacts of El Niño–Southern Oscillation (ENSO) on the intensity of synoptic‐scale disturbances (SSDs) over the tropical western North Pacific (TWNP) during boreal summer. Asymmetric changes in the SSD intensity are detected in El Niño (EN) and La Niña (LN) developing summers. The increase in the SSD intensity is larger and located more eastward in EN developing summers compared to the decrease in LN developing summers. The asymmetric SSD intensity changes are associated with an eastward shift of anomalous low‐level cyclone and mid‐level ascent during EN developing summers relative to opposite anomalies during LN developing summers. The above difference is attributed to zonally asymmetric anomalous equatorial central‐eastern Pacific heating and cooling in EN and LN years. Sensitivity experiments with an atmospheric general circulation model illustrate that the major reason for asymmetric TWNP SSD intensity changes is the asymmetric atmospheric response to opposite sea surface temperature (SST) anomalies in EN and LN years. Comparisons between strong and moderate ENSO events show an obvious dependence of the SSD intensity change on the amplitude of EN, but not on the amplitude of LN. This indicates a stronger sensitivity to warmer SST than to colder SST. The enhancement of the TWNP SSD intensity is confined to a more westward longitude in Central than Eastern Pacific EN years with a comparable magnitude.

Change of marine redox environment in the western Okinawa Trough since the mid-Holocene: Evidence based on geochemical records

The marine redox environment (MRE) plays a crucial role in the conversion and preservation of seafloor material and is a significant factor in the ocean carbon cycle. The evolution and driving mechanism of MRE are complex and present distinct regional characteristics over different time scales. The Okinawa Trough, situated in the East Asian monsoon realm, is influenced by the Kuroshio Current and flushing water, and its closed geographical pattern and multiple environmental factors make it highly sensitive to climate and marine environment changes. In this study, sediment samples from core GHN056–09 retrieved in the western Okinawa Trough were analyzed to investigate the high-resolution evolution of MRE since the mid-Holocene. The concentration of redox-sensitive elements (V, Co, Ni) and total organic carbon (TOC) were measured. Co/Ni and V/(V+Ni) values in the sediment samples indicated predominantly oxic conditions with matching productivity levels indicated by TOC (in the range of 0.28–1.17%). The oxic condition decreased during 6500–1500 a BP, and a strengthening trend was identified from 1500 a BP to present. By comparing these records with climate and environmental records, we found that weaker El Niño-Southern Oscillation (ENSO) and northward position of Intertropical Convergence Zone (ITCZ) resulted in less monsoon precipitation into the Okinawa Trough. Thinner freshwater lids could enhance seawater mixing at different layers, leading to strong oxic conditions. In contrast, stronger ENSO and southward position of ITCZ controlled by stronger solar insolation supplied more freshwater into the Okinawa Trough. Thicker freshwater barriers blocked the exchange of seawater from bottom to surface, resulting in weak oxic conditions. The trace element records in this study provide robust evidence on the high-resolution variability of MRE driven by the frequency of ENSO, movement of ITCZ, and changes in regional precipitation. Our findings offer new insights into the evolution of MRE in response to global and local climate changes.

ENSO skewness hysteresis and associated changes in strong El Niño under a CO2 removal scenario

El Niño-Southern Oscillation (ENSO) sea surface temperature (SST) anomaly skewness encapsulates the nonlinear processes of strong ENSO events and affects future climate projections. Yet, its response to CO2 forcing remains not well understood. Here, we find ENSO skewness hysteresis in a large ensemble CO2 removal simulation. The positive SST skewness in the central-to-eastern tropical Pacific gradually weakens (most pronounced near the dateline) in response to increasing CO2, but weakens even further once CO2 is ramped down. Further analyses reveal that hysteresis of the Intertropical Convergence Zone migration leads to more active and farther eastward-located strong eastern Pacific El Niño events, thus decreasing central Pacific ENSO skewness by reducing the amplitude of the central Pacific positive SST anomalies and increasing the scaling effect of the eastern Pacific skewness denominator, i.e., ENSO intensity, respectively. The reduction of eastern Pacific El Niño maximum intensity, which is constrained by the SST zonal gradient of the projected background El Niño-like warming pattern, also contributes to a reduction of eastern Pacific SST skewness around the CO2 peak phase. This study highlights the divergent responses of different strong El Niño regimes in response to climate change.

Contributions of Climate Change and ENSO Variability to Future Precipitation Extremes Over California

AbstractThe El Niño/Southern Oscillation (ENSO) affects the occurrence frequency and intensity of extreme precipitation through modulations of regional heat and moisture fluxes. California experiences particularly strong ENSO influences and models project different to its extreme precipitation. It remains unclear how diverse projections of future precipitation extremes relate to inter‐model differences for those changing signals. Here, we use “large ensemble” simulations with multiple climate models along with the Coupled Model Intercomparison Project Phase 5 to investigate the range of precipitation extreme changes over California and the influences from ENSO‐related teleconnections. We found that precipitation amount increases are much larger during El Niño relative to La Niña years, mainly caused by the differences in frequency of extreme events during different phases. The ENSO‐driven effect is even larger than the overall climate change signal for the most extreme events, implying uncertainties from inter‐model differences in ENSO‐related SST variability for extreme precipitation changes.

Space-Time Causality Analysis of Regional Impacts of ENSO on Terrestrial and Oceanic Precipitation

Future changes are expected in precipitation under climate change, therefore, changes are projected in the oceanic and terrestrial components. However, it remains poorly elucidated how the El Niño–Southern Oscillation (ENSO) can influence these changes. Therefore, we aimed to perform a space-time causality analysis of regional ENSO impacts on terrestrial and oceanic precipitation by using the Granger causality method as a function of eight temporal lags (lags 1–8). The monthly values of total precipitation obtained using the Lagrangian approach and their respective terrestrial (PLT) and oceanic (PLO) components were used. The analysis was performed for the two regions of western North America (WNA) and eastern South America (ESA) with strong ENSO signals. For the WNA region in winter, the maximum Granger causality was observed in the component of oceanic origin for temporal lags 1 and 2 (3 and 6 months), with a predominance of both positive and negative ENSO conditions. For the ESA region, it was verified that the causality of the ENSO index was maximum for PLT. Temporal lags 2–5 (6–15 months) stood out in winter when there was a marked region of the Granger causality over the La Plata Basin. In autumn, for lags 1–4 (3–12 months), the Granger causality values were predominant in the southern and western areas of ESA and showed a tendency to move northward with an increased temporal lag. Finally, it was shown that high correlation values did not imply the causality of the relationship between the ENSO index and precipitation in the two regions.

Keterkaitan Antara El Niño-Southern Oscillation (ENSO) Dengan Variabilitas Curah Hujan Bojonegoro

Indonesian climate, especially Java Island have been associated with El Niño-Southern Oscillation (ENSO). The research using rainfall station at Bojonegoro District from 1979 – 2009 to detect rainfall variability and its linkages with ENSO phenomenom. ENSO’s indexes then used to predict rainfall in Bojonegoro. Rainfall station was clustered using cluster analysis and then Mann-Kendall test used to predict rainfall trend of each cluster. There are 16 rainfall station that passed the rainfall test that can be conduct in the rainfall anomaly analysis. All stations have experienced both dry and wet anomalies during observation. Positive ENSO years have associated with more stations experienced dry anomalies; in other hand wet anomalies occurred more when negative ENSO. The stronger ENSO caused more extrem anomalies. There are obtained 5 clusters rainfall area over Bojonegoro District used HCA Ward method. Largest rainfall variations was experienced by cluster 5, Gondang and Jatiblimbing. Trend in rainfall only experienced by cluster 2 (Sumberejo and Mekuris) for December – January but another clusters didn’t experience such significant rainfall pattern change. October and November have been the most influenced month caused by ENSO; and positive ENSO anomaly caused prolonged dry season up to November. October and November’s rainfall can be predicted using SSTA Nino 3.4 index 3 months before.

Climatic and Vegetation Response Patterns over South Africa during the 2010/2011 and 2015/2016 Strong ENSO Phases

El Niño-Southern Oscillation (ENSO) is a significant climate phenomenon on Earth due to its ability to change the global atmospheric circulation which influences temperature and precipitation across the globe. In this study, we investigate the responses of climatic and vegetation parameters due to two strong ENSO phases, i.e., La Niña (2010/2011) and El Niño (2015/2016) in South Africa. The study aims to understand the influence of strong seasonal ENSO events on climatic and vegetation parameters over South Africa. Remote sensing data from the Global Precipitation Measurement (GPM), Moderate Resolution Imaging Spectroradiometer (MODIS), Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) and Atmospheric Infrared Sounder (AIRS) was used. The relationship between precipitation, temperature, and Normalized Difference Vegetation Index (NDVI) were studied using Pearson’s correlation. Comparison between the La Niña, neutral year, and El Niño periods showed two interesting results: (1) higher precipitation from the south coast to the east coast of South Africa, with some low precipitation in the interior during the La Niña and El Niño periods, and (2) a drop in precipitation by ~46.6% was observed in the southwestern parts of South Africa during the La Niña and El Niño events. The study further showed that wind speed and wind direction were not impacted by strong ENSO events during the MAM, JJA and SON seasons, but the DJF season showed varying wind speeds, especially on the west coast, during both ENSO events. Overall, the Pearson’s correlation results clearly showed that the relationship between climatic parameters such as precipitation, temperature, and vegetation parameters such a NDVI is highly correlated while other parameters, such as wind speed and direction, are not. This study has provided new insights into the relationship between temperature, precipitation, and NDVI in South Africa; however, future work will include other climatic and vegetation parameters such as relative humidity and net longwave radiation.

Seasonal Comparison of the Wildfire Emissions in Southern African Region during the Strong ENSO Events of 2010/11 and 2015/16 Using Trend Analysis and Anomaly Detection

This study investigates the wildfire biomass-burning emission levels during strong El Niño–southern oscillation (ENSO) events of 2010–2011 (characterized by a strong La Niña event) and 2015–2016 (characterized by a strong El Niño event) over the southern African region. Specifically, the biomass-burning parameters of black carbon (BC), carbon monoxide (CO) and sulfur dioxide (SO2) were investigated. Of interest in the current study was the strong El Niño (2015–2016) and La Niña (2010–2011) events during the main fire seasons in southern Africa, i.e., June–July–August (JJA) and September–October–November (SON). Furthermore, the study looks at how meteorological parameters (temperature and precipitation) are influenced by the two strong ENSO events. The sequential Mann–Kendall (SQMK) test is used to study the long-term trends of the emission and meteorological parameters. Anomaly detection on the long-term emission trends and meteorological parameters are performed using the seasonal and trend decomposition loess (STL) and generalized extreme studentized deviate (GESD). Overall, the results show higher emission levels of SO2, CO, and BC during the JJA season compared to the SON season. The SQMK results show an increasing trend of SO2, CO, and BC over time, indicating an increase in the amount of biomass burning. The GESD showed significant anomalies for BC, SO2, and CO emanating from the two strong El Niño and La Niña events. On the other hand, no significant anomalies were detected for temperature and precipitation. The results in this study highlight the significant effect of strong ENSO events on wildfire emissions, thus retrospectively showing the potential effect of future events, especially in the context of climate change.

Heatwave Variability and Structure in South Africa during Summer Drought

Pronounced subsidence leading to summer drought over southern Africa causes warmer than average surface air temperatures or even heatwave (HW) conditions. We investigated the occurrence of HWs during the summer drought over South Africa based on station data and the ECMWF ERA5 reanalyses. Temperature observations from the South African Weather Service were analyzed for seasonality and long-term trends (1981–2020) as background to the occurrence and variability of HWs. We focused on three severe El Niño Southern Oscillation (ENSO)-induced drought seasons, i.e., 1982/83, 1991/92, and 2015/16, to investigate HW characteristics. While 1997/98 was among the strongest El Niño seasons, the impacts were not as severe because it coincided with an intense Angola low, which allowed for rain-bearing cloud bands to form. Results showed that the hottest months were spread across the austral summer season from December to February. Regions experiencing high mean maximum temperatures and high HW frequencies exhibited a strong ENSO signal, with record HWs occurring during 2015/16. The establishment and persistence of a middle-level high-pressure system over Botswana/Namibia (Botswana High) appears to trigger the longest-lasting HWs during drought seasons. The Botswana high is usually coupled with a near-surface continental heat low and/or tropical warm air advection towards the affected region. It was also found that intense ENSO-induced drought events coincided with high HW frequency over South Africa, such as during 1982/83, 1991/92, and the recent 2015/16 events. The results of this study contribute to understanding drought and heat wave dynamics in a region experiencing rapid warming as a result of climate change.

Regional differences in summer monsoon precipitation variability reconstructed from multiple proxies in Asia during the past millennium

AbstractRainfall in the Asia summer monsoon (ASM) domain has a complex spatial pattern with the temporal variability at different timescales and their long‐term change has not been fully characterized. An updated 320 multiple proxies network is used to reconstruct the May–October precipitation during the past millennium for eight regions in the ASM domain. The spatial consistency of summer monsoon precipitation variability and the possible links to the internal climate oscillations are investigated. The results show that the regional precipitations over the last millennium in the ASM regions are dominated by the interannual cycle of 2–2.5a and 3.5‐5a, the decadal cycle of ~11a and 15–25a and the multidecadal cycle of ~30a and 40–80a. Coherent dry decades in different regions appear in 1100–1250, 1600–1650 and 1960–2000, while the wet decades appear in 970–990, 1330–1350, 1380–1430, 1550–1580, 1700–1780 and 1810–1910. On interannual scale, the relationships between precipitation for each region and El Niño–Southern Oscillation (ENSO) in both developing and decaying stages are unstable over the entire millennium, but they have opposite‐sign correlations most of the time, which implies that the summer precipitation anomaly for a region tends to reverse in the next summer when a strong ENSO event occurs in the winter. For the long‐term change from multidecadal to centennial scales, the longest dry period of the 12th to 13th centuries in eastern Asia coincides with the period with the lowest ENSO variability due to the in phase change of the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation, which could result in the neutral interbasin east–west cell in Tropics and low frequency of ENSO events.

ENSO atmospheric feedbacks under global warming and their relation to mean-state changes

Two atmospheric feedbacks play an important role in the dynamics of the El Niño/Southern Oscillation (ENSO), namely the amplifying zonal wind feedback and the damping heat flux feedback. Here we investigate how and why both feedbacks change under global warming in climate models participating in the 5th and 6th phase of the Coupled Model Intercomparison Project (CMIP5 and CMIP6) under the business-as-usual scenario (RCP8.5 and SSP5-8.5, respectively). The amplifying zonal wind feedback over the western equatorial Pacific (WEP) becomes significantly stronger in two third of the models, on average by 12 ± 7% in these models. The heat flux damping feedback over the eastern and central equatorial Pacific (EEP and CEP, respectively) increases as well in nearly all models, with the damping effect increasing on average by 18 ± 11%. The simultaneous strengthening of the two feedbacks can be explained by the stronger warming in the EEP relative to the WEP and the off-equatorial regions, which shifts the rising branch of the Pacific Walker Circulation to the east and increases the mean convection over the CEP. This in turn leads to a stronger vertical wind response during ENSO events over the CEP that strengthens both atmospheric feedbacks. We separate the climate models into sub-ensembles with STRONG and WEAK ENSO atmospheric feedbacks, as 2/3 of the models underestimate both feedbacks under present-day conditions by more than 40%, causing an error compensation in the ENSO dynamics. The biased mean state in WEAK in 20C constrains the ENSO atmospheric feedback projection in 21C, as the models of the WEAK sub-ensemble also have weaker ENSO atmospheric feedbacks in 21C. Further, due to the more realistic dynamics and teleconnections, we postulate that one should have more confidence in the ENSO predictions with models belonging to the STRONG sub-ensemble. Finally, we analyze the relation between ENSO amplitude change and ENSO atmospheric feedback change. We find that models simulating an eastward shift of the zonal wind feedback and increasing precipitation over the EEP during Eastern Pacific El Niño events tend to predict a larger ENSO amplitude in response to global warming.

The Interdecadal Change of the Relationship Between North Indian Ocean SST and Tropical North Atlantic SST

AbstractThe summertime North Indian Ocean (NIO) and tropical North Atlantic (TNA) sea surface temperature (SST) anomalies exert important impacts on atmospheric circulation and climate variation. Little attention is paid on the interdecadal change of NIO–TNA SST connection. This study reveals that the NIO–TNA SST relationship experiences an obvious interdecadal change around the early 2000s. The NIO and TNA SST correlation is positive and significant before the early 2000s, while this connection becomes weak and insignificant after that. This interdecadal change is closely associated with the changes in the El Niño‐Southern Oscillation (ENSO) intensity. During 1980–2001, strong ENSO forces a sustained SST warming in the southwest Indian Ocean, which further warms the summertime NIO via inducing antisymmetric circulation and reducing the upward surface latent heat flux. Meanwhile, strong ENSO forces a summertime TNA warming via arousing the Pacific North American (PNA) teleconnection. The PNA weakens the TNA trade winds, then reduces the upward surface heat flux and consequently warms the TNA. Thus, NIO and TNA SST connection is established via ENSO events during 1980–2001. In contrast, during 2002–2020, the summertime NIO SST anomaly is still related to ENSO. However, the connection between the TNA SST anomaly and ENSO is interrupted due to the weak ENSO intensity. Such weak ENSO yields a much weaker PNA teleconnection, which is inefficient to generate the TNA warming. Further analysis shows that the TNA warming during 2002–2020 is generated mainly by the negative North Atlantic Oscillation. Therefore, the connection between NIO and TNA SST anomalies collapses under the weak ENSO condition.

Analysis of wildfires and associated emissions during the recent strong ENSO phases in Southern Africa using multi-source remotely-derived products

In southern Africa, drier conditions are more pronounced during the El Niño Southern Oscillation (ENSO) years, triggering wildfire activity and extreme drought conditions which, individually or together, lead to loss of crop productivity, deaths of livestock and wildlife, famine, degraded ecosystems, water quality and quantity. However, the fire characteristics in relation to the emissions from biomass burning and surface properties are only examined to a limited extent in the literature, especially in Africa, where anthropogenic activities largely determine the fire activity. This study uses the available data from multi-source remote sensing platforms to (1) analyse the spatial distribution of wildfires and associated emissions during strong El Niño (2015/2016) and La Niña (2010/2011) phases in southern Africa, and (2) examine the effects of the severe El Niño and La Niña years on the relationship between the emission parameters, vegetation parameters and climatic parameters. Generally, the results suggest more emissions from the wildfire in the El Niño phase than that of the La Niña. Overall, the Pearson’s correlation clearly shows the influence and the relationship between the climate parameters themselves and also with emission parameters.

Impact of reduced ENSO variability and amplitude on ISMR prediction in the long‐lead forecasts of monsoon mission CFS

AbstractDespite the reduction in interannual variability and amplitude of El Nino Southern Oscillation (ENSO) after 2000, its influence on Indian summer monsoon rainfall (ISMR) is stronger than in the previous decades. Meanwhile, our analysis with high‐resolution Monsoon Mission Climate Forecast system (MMCFS, ~38 km horizontal resolution) indicates a sharp decrease in ISMR skill and ENSO–ISMR teleconnection since 2000 at long lead (3 months, Feb IC) hindcasts. At the same time, ISMR skill is intensified for a short lead (1 month, Apr IC). The persistence skill of ENSO decreased after 2000, but the decrease is more severe for January–March initial months. So the ENSO skill will be lower for models initialized during these months compared with other months. Also, the Feb IC hindcast has a similar ENSO teleconnection pattern during both periods and hence it failed to capture the modified influence of ENSO after 2000, such as the absence of dipole anomalies in the Indian Ocean and stronger subsidence over India. Thus, the model hindcasts that depend heavily on ENSO teleconnection for ISMR simulation have reduced skill in recent years. The role of other predictors along with ENSO for Apr IC hindcasts is hence evident in the current period. It is shown that after 2000, tropical Atlantic SST anomalies contributed significantly to ISMR interannual variability in observations. In these, Atlantic Meriodnal Mode (AMM) influences ISMR through off‐ equatorial circulation in absence of ENSO during the second period. Atlantic zonal mode has a weaker influence in absence of ENSO during both periods. Atlantic SST influence on ISMR is captured by April IC hindcasts during period 2, while Feb IC has the opposite relationship. Thus, the presence of another predictor in the form of tropical Atlantic SST along with strong ENSO–ISMR teleconnection makes the short lead hindcast of ISMR more skilful in the recent period for MMCFS.

Contributions of oceanic and continental AAM to interannual variation in ΔLOD with the detection of 2020–2021 La Nina event

As a strong climate element on interannual scales, the El Nino-Southern Oscillation (ENSO) is a major component of global weather and climate change, and it is also closely related to the interannual atmospheric angular momentum (AAM) and length-of-day changes (ΔLOD). Here, we reprocess and compare the interannual variations of AAM, ΔLOD with ENSO indices, with AAM mass and motion terms calculated over land separately from those over the ocean. Three oscillatory components (at ~ 6, ~ 7, ~ 8 years), due to angular momentum changes in Earth's interior, are removed to obtain the interannual ΔLOD solely related to climatic variations. Our results show that the AAM motion term over the ocean contributes the most to interannual ΔLOD, and that the oceanic AAM has larger variability than that over land, especially during the periods of strong ENSO events. After subtracting contributions associated with interior processes, the interannual ΔLOD anomalies corresponding to extreme ENSO events (1982–1983 ~ 0.43, 1997–1998 ~ 0.36, 2015–2016 ~ 0.42 ms) are about half as strong as those found in previous studies (~ 0.91, ~ 0.76, ~ 0.81 ms). Furthermore, we detect an intermediate La Nina event that occurred from August 2020 to May 2021, forcing the interannual ΔLOD to a minimum value of approximately -0.21 ms.